The ISTIL Laboratory of Photometry and Radiometry of Light Pollution

The ISTIL Laboratory of Photometry and Radiometry of Light Pollution (LPLAB)

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Manager: Dr. Pierantonio Cinzano

Keywords

Light Pollution, Night Sky Brightness, Photometry, Imaging Photometry, Spectral Radiometry, Hyperspectral Imaging, Bidirectional Reflectance BDRF, Remote Sensing, DMSP, Calibration, Outdoor Lighting, Glare, Environment.

Purpose

The Laboratory of Photometry and Radiometry of Light Pollution (LPLAB) was set up to provide the Light Pollution Science and Technology Institute (ISTIL) of instruments and calibration services to support its scientific and technological research on light pollution and related environmental effects. ISTIL is a no-profit institute. Started in late 2001, LPLAB is probably the first laboratory born specifically and exclusively to study light pollution.

Research

With the instrument of the laboratory a number of studies and collaborations are carried on, like the project Global monitoring of light pollution and night sky brightness from satellite measurements, supported by the Italian Space Agency, and the project Light pollution and the situation of the night sky at astronomical sites carried on at the University of Padova, Italy.

Description

The laboratory equipments are characterized by low light intensity measurement and calibration capabilities and by the portability typically required by on-site measurements. Some of them have been set up for the specific needs of this field of study. Photometric and radiometric calibration services are provided by the laboratory to ensure that instruments are accurate and NIST traceable.

Measurements and Instruments

The laboratory in practice consists of different instruments and calibration equipments. The measurement capabilities and the calibration standards are:

§ Measurements of luminance in CIE Photopic and CIE Scotopic passbands

§ Measurements of illuminance

§ Measurements of irradiance

§ Measurements of Photosynthetic Active Radiation (PAR) photon irradiance

§ Measurements of photon radiance and Photosyntetic Active Radiation (PAR)

§ Mapping of night sky brightness at sites in CIE Photopic passband, CIE Scotopic passband and UBVRI astronomical photometrical bands with atmospheric extinction

§ Hyperspectral mapping of the night sky at sites

§ Polarimetry and spectropolarimetry of the artificial night sky brightness

§ Measurements of night-time radiance of the Earth surface

§ Measurements of upward light emissions by polluting areas

§ Imaging of light emissions in CIE Photopic response, CIE Scotopic response, UBVRI photometrical astronomical bands and other passbands

§ Measurements of veiling luminance and disability glare

§ Hyperspectral imaging of polluting areas and lighting installations

§ Spectroradiometric measurements of light sources

§ Measurements on-site of upward light intensity of individual luminaries

§ Measurements on-site of bi-directional reflectance (BDRF)

§ Measurements of the building screening angle at a luminaire site

§ Spectral irradiance and illuminance calibration

§ Radiance and luminance calibration

§ Wavelength calibration

§ Spectral responsivity calibration

§ Reflectance standard

Measurements of luminance in CIE Photopic and CIE Scotopic passbands

Luminance: Luminous intensity of the light leaving a surface in a given direction divided by the apparent area of the surface, i.e. the projection of its area on a plane perpendicular to that direction.

Instruments: Portable Research Radiometer International-Light IL1700, SLR spot portable Luminance Meter Minolta LS-100, Portable Quantum Radiometer Macam Q203 with spot luminance probe, WASBAM photometric imaging camera

Parameter

Description

Instrument

Research Radiometer IL1700

Manufacturer

International-Light, Newburyport, MA Serial Number 4358

IL1700 dynamic range

2x10-13 to 2x10-3 Amps.

Min. resolution

0.01x10-11 Amps.

Linearity

±0.1%, top 8 decades

±0.2%,+-1 digit, bottom 2 decades

Calibration Accuracy

±0.2%, 1mA to 2 mA

±0.5%, 1nA to 1mA

±1% below 1 nA

Detector

SHD033 33 mm² Silicon

Serial Number 336

Spectral range

200 nm –1050 nm

Typical peak responsivity

66 A W^-1 cm²at 760 nm

Temperature stabilization

-80°C to +50°C

Lens

L30 High Gain Lens

Diameter

37 mm

Field-of-view

± 8°

Linearity and repeatability

±1% at upper ranges

±2.3% at lower range

Accuracy relative to NIST (luminance)

± 4.3% (NIST uncertainty to ISO ±0.31%)

± 4.3% + ±2.3% in the last two decades

Accuracy relative to NIST (brightness)

± 4.9%

± 4.9% + ±2.3% in the last two decades

Minimum measurable luminance

7x10^-7 cd/m2 in CIE photopic band

9x10^-7 cd/m2 in CIE scotopic band

Minimum measurable brightness

25 mag/arcsec² in V band (Landolt 1992 )

Parameter	Description
Instrument	SLR spot Luminance meter LS-100
Manufacturer	Minolta Co. Ltd, Osaka, Japan Serial number: 78213014
Minimum luminance	0.001 cd/m²
Accuracy (relative to NIST)	± 2 % ± 2 digits (Illuminant A)
Repeatability	± 0.2% ± 2 digits in the range 0.001-0.999 cd/m2 (Illuminant A)
Spectral Response	within 8% (f1’) of the CIE Photopic spectral luminous efficacy (1924)
Acceptance angle	1° at infinity (<0.1% at 45’ from the centre)
Temperature/humidity drift	± 3% ± 1 digit of value displayed at 20°C in the range 0°-40°C, humidity at 85%

Parameter	Description
Instrument	Quantum Radiometer Macam Q203 + spot luminance probe
Manufacturer	Macam Photometrics Ltd, Livingston, Scotland Serial number: 7265
Minimum luminance	0.001 cd/m² photopic 0.001 cd/m² scotopic
Repeatability	± 1 % ± 1 digit
Calibration accuracy	± 5 % (relative to NPL)
Spectral Response	within 5.08% (f1) of the CIE Photopic spectral luminous efficacy (1924)
Acceptance angle	6°


Parameter	Description
CCD	Kodak KAF0401E Full Frame Non-ABG
A/D Resolution	16 bits (max 65535 counts)
Array size	6.9 x 4.6 mm / diagonal 8.28 mm
Pixel number	510 x 765
Pixelsize	9 x 9 μ
Electrons per A/D count	~2.3 e-/ADU
Read noise	15 electrons rms
Bias	~ 100 ADU
Dark currents	Less than 1 e- pixel-1 s-1 at 0 °C
Full Well Capacity / Saturation	100.000 electrons/~40.000-34000 ADU
Exposition min/max/resolution	0.11 s/ 3600 s/ 10 ms
Field of view with 16 mm f 2.8 lens	16.4 x 24.6 degrees
Scale with 16 mm f 2.8 lens	~115.875”/pixel, 1.93’/pixel
Camera	SBIG ST-7E NABG Serial 01062868E
Shutter	electromechanic
Cooler	solid state thermoelectric Peltier cooler
Readout	double correlated sampling
Lens	Zenitar 16 mm f 2.8
Filter wheel /diameter	SBIG CFW-8
CCD spectral response	430nm-830nm FWHM
WASBAM spectral responses	within 10.5% (f1) of the CIE Photopic spectral luminous efficacy (1924) within 9.9% (f1) of the CIE Scotopic spectral luminous efficacy (1951)

Research radiometer with the high gain scotopic luminance probe

Radiometer spectral responses (blue) compared with the standard responses (violet) and the detector response (red): CIE Photopic (1924), CIE Scotopic (1951), V band (Landolt 1992).

SLR luminance meter

Spot luminance probe

Measurements of illuminance

Illuminance: Light flux incident upon a surface divided by the area of the surface

Instrument: Portable Quantum Radiometer Macam Q203 with cosine corrected illuminance probe

Parameter	Description
Instrument	Quantum Radiometer Macam Q203 + illuminance probe
Manufacturer	Macam Photometrics Ltd, Livingston, Scotland Serial number: 7265
Minimum illuminance	0.001 lx
Repeatability	± 1 % ± 1 digit
Calibration accuracy	± 5 % (relative to NPL)
Spectral Response	within 5.11% (f1) of the CIE Photopic spectral luminous efficacy (1924)
Cosine correction	± 3 % to 70°

Portable quantum radiometer

Measurements of irradiance

Irradiance: Radiant flux per unit area (flux density)

Instrument: Portable Quantum Radiometer Macam Q203 with cosine corrected probe and flat filter

Parameter	Description
Instrument	Quantum Radiometer Macam Q203 + irradiance probe
Manufacturer	Macam Photometrics Ltd, Livingston, Scotland Serial number: 7265
Minimum irradiance	0.01 mW/m²
Repeatability	± 1 % ± 1 digit
Calibration accuracy	± 7.5 % (relative to NPL)
Spectral Response	Flat energetic response in the range 400nm-1070nm
Cosine correction	± 3 % to 70°

Irradiance probe

Measurements of Photosynthetic Active Radiation (PAR) photon irradiance.

Photon irradiance: number of photons received per unit time on an unit area

Photo Active Radiation: The photons in the wavelength range 400nm–700nm. They have great interest for plant science due to their photosynthetic efficiency. The number of photons in the range 400nm –700nm received per unit time on a unit area is also called Photosynthetic Photon Flux Density (PPFD). It must not be mistaken with the Photosynthetic Photon Flux Fluence Rate (PPFFR), also called spherical irradiance, which is the integral over all directions of the photon radiance at a point.

Instrument: Portable Quantum Radiometer Macam Q203 with quantametric cosine corrected probe.

Parameter	Description
Instrument	Quantum Radiometer Macam Q203 + quantametric cosine corrected probe
Manufacturer	Macam Photometrics Ltd, Livingston, Scotland Serial number: 7265
Minimum photon irradiance	0.001 mE s^-1 m^-2; 6 10²⁰ ph s^-1 m^-2
Repeatability	± 1 % ± 1 digit
Calibration accuracy (relative to NPL)	± 7.5 %
Spectral Response	Flat quantum response in the range 400nm-700nm
Cosine correction	± 3 % to 70°

Quantametric probe

Measurements of photon radiance and Photosynthetic Active Radiation (PAR).

Photon radiance: number of photons received per unit time on a unit area from a unit solid angle

Photo Active radiation: (see above)

Instrument: see “Imaging of light emissions”.

Mapping of night sky brightness at sites in CIE Photopic passband, CIE Scotopic passband and UBVRI astronomical photometrical bands with atmospheric extinction

Night sky brightness: General term indicating the flux arriving from a unit solid angle of night sky in a unit area of detector. In dependence of the kind of flux and the spectral response of the measuring system, it correspond to different quantities and units. E.g. light or energy in CIE response band (luminance, cd m^-2), photons (photon radiance, ph s^-1 m^-2sr^-1), energy (radiance, W m^-2sr^-1), photons or energy in astronomical photometrical bands (brightness, mag arcsec^-2), etc.

Instrument: WASBAM (Wide Field Sky Brightness Automatic Mapper)

Description: Many studies of light pollution require large quantities of measurements of night sky brightness that, in order to be useful, need to be associated with knowledge of atmospheric conditions during the measurements (e.g. Cinzano et al. 2000; Cinzano, Falchi & Elvidge2001a,b). The measure of the atmospheric extinction is one of the simpler ways to evaluate the aerosol content of the atmosphere. In order to obtain contemporary measurements of night sky brightness below the atmosphere and stellar extinction, ISTIL set up a specific instrument called WASBAM (Wide-Angle Sky Brightness Automatic Mapper). The basic requirements were: 1) fast and automatic coverage of the entire sky in astronomical photometrical bands with a series of wide-field images; 2) maximum lightness, transportability and quick set-up in order to take measurements from more sites in the same night; 3) easily available commercial components and control software so that the same instrument could be easily set up by any interested institution, included amateurs astronomers groups and sections of the International Dark-Sky Association (IDA); 4) automatic registration of position, elevation, date, time, alt-azimuthal and equatorial celestial coordinates; 5) quick data reduction, automatized as much as possible.

We coupled a small ultra-light computerized altazimuthal mount with a cooled CCD camera, a wide field lens and an automatic filter-wheel to allow the fully control of the instrument from a portable computer. The software automatically controls all the operations from the pointing and the coordinate memorization (both altazimuthal and equatorial) to the management of the CCD and the filter wheel. The set-up procedure (Cinzano 2002a) is quite fast, mainly requiring to place the instrument, insert the geographical position obtained with a GPS receiver, tune the alignment with two stars chosen by the instrument and start the computer procedure. The instrument automatically exposes a sequence of sky zones, e.g. the zenith, 8 zones at 45° altitude equally spaced in azimuth along the horizon and 12 zones at 20° altitude every 30° in azimuth. At the end, after the exposure of some flat-field, it is possible to move to the next site. The software allows to reduce all the images together with the standard procedure and determines the astrometry recognizing the standard stars to be used for the photometrical calibration and the extinction curve (Cinzano 2002b).

Parameter	Description
CCD	Kodak KAF0401E Full Frame Non-ABG
A/D Resolution	16 bits (max 65535 counts)
Array size	6.9 x 4.6 mm / diagonal 8.28 mm
Pixel number	510 x 765
Pixelsize	9 x 9 μ
Electrons per A/D count	~2.3 e-/ADU
Read noise	15 electrons rms
Bias	~ 100 ADU
Dark currents	Less than 1 e- pixel-1 s-1 at 0 °C
Full Well Capacity / Saturation	100.000 electrons/~40.000-34000 ADU
Exposition min/max/resolution	0.11 s/ 3600 s/ 10 ms
Field of view with 16 mm f 2.8 lens	16.4 x 24.6 degrees
Scale with 16 mm f 2.8 lens	~115.875”/pixel, 1.93’/pixel
Camera	SBIG ST-7E NABG Serial 01062868E
Shutter	electromechanic
Cooler	solid state thermoelectric Peltier cooler
Readout	double correlated sampling
Mount	Alt-azimuthal Celestron Nextar 4
Lens	Zenitar 16 mm f 2.8
Filter wheel /diameter	SBIG CFW-8
CCD spectral response	430nm-830nm FWHM
WASBAM spectral responses	B band (Landolt 1992), V band (Landolt 1992), R band (Landolt 1992), CIE Photopic (1924), CIE Scotopic (1951)

WASBAM

Hyperspectral mapping of the night sky at sites

Spectral radiance: Radiance per unit wavelength. Measured for each direction (elevation, azimuth) of the chosen grid.

Instrument: WASBAM with Small Spectroscopic Head (SSH)

Description: Automatic mapping of the entire sky of a site with a sequence of spectra. A spectrographic head with a De Amici prism allows WASBAM (see description above) to take spectra of the sky background with a dispersion better than 1 nm pixel-1 at 550 nm.

Parameter	Description
Manifacturer	Browning, London, UK
Dispersing device	De Amici prism
Lens	Tessar-like D=17 mm F=30 mm
Lens manifacturer	Costruzioni Ottiche Zen, Venice, Italy
Wavelength standard	Hg-Ar portable standard source
Dispersion	better than 1 nm pixel-1 at 550 nm
Slit width	adjustable
Wavelength range	430nm-1000nm adjustable

WASBAM with Small Spectroscopic Head

Uncalibrated spectra of the night sky taken with WASBAM-SSH

Polarimetry and spectropolarimetry of the artificial night sky brightness

Polarization: represented by the Stoke's parameters (I, Q, U), the normalized Stoke's parameters (q, u), or the degree of linear polarization and the position angle of the polarization vector (p, q).

Instrument: WASBAM photometric imaging camera, WASBAM with Small Spectroscopic Head (SSH), Portable Research Radiometer International-Light IL1700, SLR spot portable Luminance Meter Minolta LS-100, Portable Quantum Radiometer Macam Q203 with spot luminance probe.

Description: A Tech Spec glass sandwich-design Linear Polarizing Filter with diameter 50mm in a rotating mount, with 360° scaled venier, lever arm for smooth rotation and locking knob, allows measurements of the polarization of artificial light coming from each direction (elevation, azimuth) of the sky on a chosen grid. It is mounted in front of the instrument lens and manually set.

Parameter	Description
Polarizing filter and mount manufacturer	Edmund Optics Inc., Barrington, USA
Bevel	0.3mm x 45° typical, cut edges
Surface Accuracy	4 to 6 waves/inch
Operating Temperature	-15° to 70°C (5° to 158°F)
Polarization Efficiency	95% or better Polarization Efficiency (%) = 100*[(H0-H90)/(H0+H90)]^1/2 where H0 is the average transmittance (unpolarized incident light) of parallel polarizers, over 400-700nm, H90 is the average transmittance (unpolarized incident light) of crossed polarizers, over 400-700nm
Transmission, single	30% typical over 400-700nm with unpolarized light
Transmission, crossed	0.15% average over 400-700nm with unpolarized light
Maximum transmittance T1	~0.5 parallel to the plane of a linear polarized beam
Minimum transmittance T2	~0.003 perpendicular to the plane of a linear polarized beam
Extinction Ratio	~0.5 10^-2 Extinction Ratio = T2 / T1 » ½ (T^ / T\|\| ), where T\|\| = maximum transmittance of two polarizers parallel in unpolarized beam, T^ = minimum transmittance of two polarizers perpendicular in unpolarized beam

WASBAM lens and SHD033 head with Polarizer

Measurements of night-time radiance of the Earth surface

Radiance: Radiant flux per unit area per unit solid angle

Instrument: DMSP Operational Linescan System (OLS)

Description: Our surveillance of the night sky is also based on the measurements of the global night-time radiance of the sources on the Earth surface made by the satellites of the Defense Metereological Satellite Program (DMSP) of the United Stated Air Force. We collaborate with the NOAA National Geophysic Data Center of Boulder which archives DMSP data. The DMSP satellites are in polar orbit and carry an oscillating scan radiometer, the Operational Linescan System (OLS), with a photomultiplier tube detector (PMT). The OLS scans a narrow swath of the Earth, about 3,000 km wide, perpendicular to the orbit and as the satellite moves it constructs a bi-dimensional image of the Earth surface’s radiance. We evaluate the upward light flux of sources on the Earth surface with DMSP-OLS data and then we compute the effects on the night sky due to the scattering and propagation of the light in the atmosphere. For details see www.lightpollution.it/dmsp/ and for our papers see http://www.lightpollution.it/cinzano/papers.html .

Parameter	Description
Instrument	Operational Linescan System
Description	Oscillating scan radiometer for low light imaging
Satellites	USAF/DMSP
Digital Archive	NOAA National Geophysical Data Center, Boulder
Orbit	Sun-synchronous polar
Orbital period / Altitude	101 min / 830 km
Bands	Visible and near Infrared (TIR)
Visible Response	485 nm – 765 nm FWHM with max at 500-600 nm
Detector (Visible)	Photomultiplier tube (PMT)
TIR Response	10.3-12.9 mm FWHM
Data swath size	3000 km
Ground Sampling Distance	~0.56 km (~2.8 km for averaged data)
Effective Instantaneous Field of View (EIFOV)	From 2.2 km at nadir to 5.4 km at scan edge
Minimum radiance	10^-5 to 10^-6 W m^-2 sr^-1 above the atmosphere
Minimum luminance	0.2 to 3 mcd m^-2 above the atmosphere
Minimum luminance	~4 kcd km^-2 on the ground

Measurements of upward light emissions by polluting areas.

Instruments: SLR spot portable Luminance Meter Minolta LS-100 with Solatronic Digital Inclinometer and GPS receiver; Portable Quantum Radiometer Macam Q203 with spot luminance probe together with Solatronic Digital Inclinometer and GPS receiver; WASBAM photometric imaging camera with Solatronic Digital Inclinometer and GPS receiver.

Description: For spot luminance measurements see above “Measurements of luminance in CIE Photopic and CIE Scotopic passbands”. For imaging see ”Imaging of light emissions in CIE Photopic passband, CIE Scotopic passband, UBVRI photometrical astronomical bands and PAR passband.” For the measure of the inclination angle of the observed light see “Measurements on-site of upward light intensity of individual luminaries”. For the measurement of the geographical position of the observing point, a GPS receiver is used.

Imaging of light emissions in CIE Photopic response, CIE Scotopic response, UBVRI photometrical astronomical bands and other passbands.

Instruments: WASBAM imaging camera

Description: WASBAM imaging camera allows to take images of light installations, lighted areas or landscapes in a number of passbands, which in turn allow to evaluate the light pollution produced in each band and to recognize lamp kinds based on their colour indexes.

Parameter	Description
CCD	Kodak KAF0401E Full Frame Non-ABG
A/D Resolution	16 bits (max 65535 counts)
Array size	6.9 x 4.6 mm / diagonal 8.28 mm
Pixel number	510 x 765
Pixelsize	9 x 9 μ
Electrons per A/D count	~2.3 e-/ADU
Read noise	15 electrons rms
Bias	~ 100 ADU
Dark currents	Less than 1 e- pixel-1 s-1 at 0 °C
Full Well Capacity / Saturation	100.000 electrons/~40.000-34000 ADU
Exposition min/max/resolution	0.11 s/ 3600 s/ 10 ms
Field of view with 16 mm f 2.8 lens	16.4 x 24.6 degrees
Scale with 16 mm f 2.8 lens	~115.875”/pixel, 1.93’/pixel
Camera	SBIG ST-7E NABG Serial 01062868E
Shutter	electromechanic
Cooler	solid state thermoelectric Peltier cooler
Readout	double correlated sampling
Lens	Zenitar 16 mm f 2.8
Filter wheel /diameter	SBIG CFW-8
CCD spectral response	430nm-830nm FWHM
WASBAM spectral responses	B band (Landolt 1992), V band (Landolt 1992), R band (Landolt 1992), CIE Photopic (1924), CIE Scotopic (1951)

Left: WASBAM imaging camera – Right: WASBAM spectral responses (red) compared with the standard responses (blue): B band (Landolt 1992), V band (Landolt 1992), R band (Landolt 1992), CIE Photopic (1924), CIE Scotopic (1951).

Measurements of veiling luminance and disability glare

Veiling luminance: a luminance superimposed on the retinal image which reduces contrast. It is the veiling effect produced by bright sources or areas in the visual field that results in decreased visual performance and visibility (IESNA-RP-33-99)

Disability glare: the effect of stray light in the eye whereby visibility and visual performance are reduced. A direct glare source that produces discomfort may also produce disability glare by introducing a measurable amount of stray light in the eye (IESNA-RP-33-99).

Instrument: WASBAM imaging camera

Description: WASBAM CCD camera (described above) allows imaging of the luminance distribution of the visual field of an observer. Based on the luminance and the angular position of each pixel in respect to the direction of observation, the veiling luminance can be easily evaluated. This method allows – when needed - to relax the hypothesis of spherical symmetry around the direction of observation in glare evaluation. The software is still under test.

Glare

Hyperspectral imaging of polluting areas and lighting installations

Instrument: WASBAM with a modified version of Small Spectroscopic Head (SSH) (under development)

Description: Hyperspectral imaging of polluting areas allows not only to have at one’s disposal the complete spectra of each point of a lighted area but also allows, with a simple integration along the wavelength, to recover at any time an image of the area in any spectral response passband, including Hg light and HPS light. It also allows to obtain an image of the colour indexes.

Spectroradiometric measurements of light sources

Spectral radiance: Radiance per unit wavelength.

Instrument: WASBAM with Small Spectroscopic Head (SSH)

Description: A spectrographic head with a De Amici prism, allows WASBAM (see description above) to take spectra.

Parameter	Description
Manifacturer	Browning, London, UK
Dispersing device	De Amici prism
Lens	Tessar-like D=17 mm F=30 mm
Lens manifacturer	Costruzioni Ottiche Zen, Venice, Italy
Wavelength standard	Hg-Ar portable standard source
Dispersion	better than 1 nm pixel-1 at 550 nm
Slit width	adjustable
Wavelength range	430nm-1000nm adjustable

Measurements on-site of upward light intensity of individual luminaries

Instruments: SLR spot portable Luminance Meter Minolta LS-100, together with a Laser Distance meter and a Digital Inclinometer.

Description: The luminance meter, if accurately characterized, allows to measure the illuminance produced by a luminaire entirely contained inside its field of view. Measuring and subtracting the background luminance, and accounting for the distance measured with the distance meter, it is possible to evaluate the intensity of the light emitted by the luminaire in the direction of the observer. The inclinometer allows to measure the emission (gamma) angle. The distance meter allows with some trigonometry to evaluate, when necessary, the azimuth angle (C-angle). Both upward and downward light emission can be measured with this method, when on-site testing of lighting installations is required.

Parameter	Description
Instrument	SLR spot Luminance meter LS-100
Manufacturer	Minolta Co. Ltd, Osaka, Japan Serial number: 78213014
Minimum luminance	0.001 cd/m²
Accuracy (to NIST)	± 2 % ± 2 digits (Illuminant A)
Repeatability	± 0.2% ± 2 digits in the range 0.001-0.999 cd/m2 (Illuminant A)
Spectral Response	within 8% (f1’) of the CIE Photopic spectral luminous efficacy (1924)
Acceptance angle	1° at infinity (<0.1% at 45’ from the centre)
Temperature/humidity drift	± 3% ± 1 digit of value displayed at 20°C in the range 0°-40°C, humidity at 85%

Parameter	Description
Instrument	Laser Distance Meter Classic 5
Manufacturer	Leica Geosystems AG, Heerbrugg, Switzerland
Range	0,3 to over 200 m
Accuracy	± 3 mm

Parameter	Description
Instrument	Solatronic Digital Self calibrating Inclinometer
Manufacturer	Sola
Accuracy	± 0.1° self calibrating from 0° to 90° , ± 0.2° from -1° to -89°
Range	0°-360°

Laser distance meter – Digital inclinometer

Measurements on-site of bi-directional reflectance (BDRF)

Bidirectional Reflectance Distribution Function (BDRF): The bidirectional reflectance is the ratio between the radiance of a given surface and the irradiance of the light incident on it, for any set of position angles of the source and the instrument. It quantifies the angular distribution of light scattered from a surface. It can be fully mapped on a four dimensional grid where each dimension is one of the four position angles. Frequently, it is tabulated only for source and instrument on the same plane, or at 45° azimuth, and for an inclination angle of the source of 8°, 30° or 45°.

Instruments: SLR spot Luminance Meter Minolta LS-100, together with Labsphere Spectralon Reflectance Standard and Solatronic Digital Inclinometer

Description: a comparison between the luminance of the object surface and the luminance measured on the reflectance standard target, allows to obtain the object surface reflectance for any given incidence and observation angles (to inclinations of 89°). The opportunity to measure the luminance on-site, allows not only to measure actual surfaces in their operative situation but also allows to use the real light source so that the measured reflectance account for the correct spectra of the incident light.

Parameter	Description
Instrument	SLR spot Luminance meter LS-100
Manufacturer	Minolta Co. Ltd, Osaka, Japan Serial number: 78213014
Minimum luminance	0.001 cd/m²
Accuracy (to NIST)	± 2 % ± 2 digits (Illuminant A)
Repeatability	± 0.2% ± 2 digits in the range 0.001-0.999 cd/m2 (Illuminant A)
Spectral Response	within 8% (f1’) of the CIE Photopic spectral luminous efficacy (1924)
Acceptance angle	1° at infinity (<0.1% at 45’ from the centre)
Temperature/humidity drift	± 3% ± 1 digit of value displayed at 20°C in the range 0°-40°C, humidity at 85%


Parameter	Description
Standard	Spectralon 99% White Reflectance Standard
Manufacturer	Labsphere Inc., North Sutton (NH) USA Serial number: 38586-I-I
8° Hemispherical reflectance	99 % from 350 to 1300 nm 95 % from 250 to 2100 nm
R(0°/45°) Bidirectional Reflectance	1.021 @550 nm
Calibration uncertainty	< 0.5 % from 300 to 2200 nm < 2 % from 250 to 2500 nm
Target reflectance uncertainty	±1% 400 nm - 990 nm
Material	Washable thermoplastic resin
Size	12.7 cm x 12.7 cm square plate

Parameter	Description
Instrument	Solatronic Digital Self calibrating Inclinometer
Manufacturer	Sola
Accuracy	± 0.1° self calibrating from 0° to 90° , ± 0.2° from -1° to -89°
Range	0°-360°

Measurements of the building screening angle at a luminaire site

Building Screening Angle: Maximum elevation over the horizon (gamma angle-90°) to which a luminaire is fully screened by surrounding buildings at any azimuth angle.

Instruments: Solatronic Digital Inclinometer and Laser distance meter.

Description: With the digital inclinometer, the minimum elevation angle at which the sky is still visible, at least in one azimuth direction, is recognized. The screening angle is measured from a place just at the nadir of the luminaire. Trigonometry allows to reduce the screening angle at the luminaire height, with the help of the distance meter and – in case – of a reasonably accurate city map.

Parameter	Description
Instrument	Solatronic Digital Self calibrating Inclinometer
Manufacturer	Sola
Accuracy	± 0.1° self calibrating from 0° to 90° , ± 0.2° from -1° to -89°
Range	0°-360°

Calibrations:

Spectral irradiance and illuminance calibration

Instrument: 1) Oriel Spectral Irradiance Standard and Optronic OL-65A Radiometric Power Supply; 2) the Moon

Description:

1) Spectral Irradiance Standard come with a complete report which describes test specifications and spectral irradiance data at 0.5m for the source. The high performance radiometric power supply provides that current uncertainty is a only a very minor source of measurement uncertainty. Black low reflectance fabric and baffles help to reduce unwanted reflections.

2) The Moon is a nice irradiance standard source (see the discussion later). However, it is easier to use it to calibrate a spot radiance or luminance meter than a cosine irradiance or illuminance meter. In facts, in order to correct for the atmospheric extinction it is necessary to make measurements with the Moon at many elevation angles, including very low elevations, so that artifices are required to avoid inclusion of light from other artificial and natural sources. On the contrary, thanks to their optical systems, luminance meters and radiance meters have narrow acceptance angles. For this reason we will discuss it in the next section.

Parameter	Description
Source	Quartz Tungsten Halogen lamp 200W
Manufacturer	Thermo Oriel, Stratford, (CT) USA Serial No. 7-1486
Spectral Range	250 nm -2400 nm
Lamp Current	6.50 Amps
Accuracy relative to NIST	± 1.85% from 350 nm to 900 nm ± 3% from 250 nm to 2000 nm


Parameter	Description
Power Supply	Radiometric Power Supply OL-65-A
Manufacturer	Optronic Laboratories inc., Orlando, FL, USA Serial No. 03211285
Current resolution	0.001 Amp
Current Accuracy	± 0.01% @ 6.500 Amps ± 0.00065 Amps @ 6.500 Amps (at 23° ±1°)
Spectral irradiance uncertainty due to error in setting current	0.04% @550 nm
Stability (after 20 min)	± 10 ppm, ± 0.001%
Line regulation	< 2 ppm/V
Maximum fluctuation for which the current accuracy is maintained	± 10% in line voltage and load voltage

Parameter	Description
Item	Low Reflectance Fabric
Distributor	Ferro, Padova, Italy
Material	Black Velvet
Reflectance	0.7% at 0°, 1% at 45° (source at -30°) 0.7% at 45°, 1% at 70° (source at -45°) in CIE photopic band

Irradiance standard - Optical bench and high performance radiometric power supply

Example: relative illuminance stability over 3 minutes (time unit is ~0.3 seconds)

Radiance and luminance calibration

Instruments: 1) Oriel Illuminance Standard Lamp, Optronic OL-65A Radiometric Power Supply and Labsphere Spectralon Reflectance Standard; 2) Variable Low-Light-Level Calibration Standard consisting of Oriel Illuminance Standard Lamp, Optronic OL-65A Radiometric Power Supply and Oriel Uniform Integrating Sphere; 3) Portable Radiance Standard Gigahertz-Optik BN0102-1; 4) The Moon and main Planets

Description: 1) Illuminating a Reflectance Standard target with a Spectral Irradiance Standard we obtain a luminance standard. See “Irradiance, spectral irradiance and illuminance calibration” for details on the Spectral Irradiance Standard and Radiometric Power Supply and “Reflectance Standard” for details on it. Even if this configuration allows one of the most accurate calibrations, and a Spectralon surface has one of the more flat spectral reflectance responses, the luminance cannot be varied quickly, requiring to move the lamp or the target, the use of a non standard distance increase the uncertainty, very low light levels cannot be reached and luminance is not expected to have an outstanding spatial uniformity.

2) The Variable Low-Light-Level Calibration Standard has been set up for calibrating and testing photometers and radiometers to very low light levels. It consists of a 8” Integrating Sphere with the entrance port illuminated by a Spectral Irradiance Standard source or some other lamps (HPS, Hg, QTH). Integrating spheres are hollow spheres which have their interior coated with a substance that is nearly perfectly diffuse or lambertian and as much spectrally flat as possible, and are widely used to calibrate spectroradiometric measurement devices. Our barium sulfate coated sphere with two in-line ports and an intermediate in-line baffle is specifically made to obtain the best radiance and luminance uniformity across the 2-inch radiating aperture. Thanks to a fixed aperture wheel, its radiance/luminance can be varied in steps over a factor 1:376. The change of the source distance from the input port, or the change of source itself, allows a further variation of 1000 when needed. When only a source of relative luminance is needed, a removable optical device with a variable aperture stop can be added to continuously regulate the starting luminance to a factor 1:45. The full range of luminance of the calibrator in both configurations, with and without optical device, goes from 1800 cd/m2 to 0.16 ucd/m2 (nominal). A shutter allows to properly measuring the stray light from background room light. A high performance radiometric power supply provides that lamp current uncertainty is a only a very minor source of measurement uncertainty. Black low reflectance fabric and baffles help to reduce unwanted reflections.

3) The Portable Spectral Radiance Standard is a compact size and light reference standard which can be used on-the-field, with a battery inverter, for the spectrophotometrical calibration of WASBAM. It consists of a small diameter OP.DI.MA integrating sphere with a symmetrical baffle which offers a 1.5% uniformity at the 20 mm diameter output port. Its tungsten halogen lamp is current controlled by the LCRT radiometric power supply. Its radiance is confirmed by a factory calibration certificate. The effects of the external temperature must be monitored and accounted for.

4) The Moon can be characterized as a quality spectral radiance calibration source. For fixed illumination and observation geometry, the Moon can be considered photometrically stable to 10^-8 per annum for irradiance and 10^-7 per annum for radiance at a resolution of about 550 km (Kieffer 1997). The Moon, however, is a variable brightness source with a complicated luminosity function and it is decidedly non lambertian. The challenge in using the Moon as a radiometric standard is in characterizing its variation of radiance and irradiance with illumination and viewing geometry (Kieffer & Wildey 1996, Kieffer & Anderson 1998). Accurate Moon radiometry is carried on by USGS Robotic Lunar Observatory and expected errors on radiance are under 1% relative and 2.5% absolute. The knowledge of the radiance distribution along the lunar disk is not required when the Moon is used only as integral illuminance/irradiance calibration source, as happen calibrating a luminance meter or a radiance meter which usually has a field of view larger than the apparent diameter of the Moon (Cinzano 2003, in prep.). In this cases these instruments are used as integral irradiance/illuminance meters and the measured value must be multiplied for the apparent area of the field-of-view of the instrument. Events that would change the Moon integral illuminance/ irradiance by 1% are expected once per 1.4 Gyr (Kieffer 1997) so that stability is of the order of 10^-9 per annum. The uncertainty on the Moon integral irradiance phase curve is approximately 5% (Lane and Irvine 1972) at which must be added the uncertainty of the calibration of the astronomical V band standards against NIST and the conversion to the CIE photopic response. The 5% accuracy of the phase curve can be improved accounting for libration effects.

Parameter

Description

Instrument	Spectral Radiance Standard
Lamp and Optical Bench Manufacturer	Thermo Oriel, Stratford, USA
Light Source	200W Oriel Irradiance Standard
Spectral calibration range	250-2400 nm
Spectral irradiance uncertainty relative to NIST	±1.85% 350-900 nm ±3% 250-2000 nm
Color Temperature	~3150 K
Target Manufacturer	Labsphere, USA
Target	Optical Grade Spectralon
R(8°/h) Hemispherical Reflectance	0.990 500-850 nm
R(0°/45°) Bidirectional Reflectance	1.021 @550 nm
Target reflectance uncertainty	±1% 400 nm - 990 nm
Incident angle	0°
View angle	45° (depending on the setup)
Radiance uniformity across the target	£ ±4% at 50 cm depending on the setup
Spectral radiance@555 nm	8.245 mW m^-2 sr^-1 nm^-1 for R=1
Typical photopic luminance	614.526 cd/m²at 50 cm for R=1
Typical scotopic luminance	951.96 cd/m² at 50 cm for R=1
Radiometric Power Supply Manufacturer	Optronic Laboratories inc., Orlando, FL, USA
Radiometric Power Supply	OL-65-A Serial No.03211285
Short Term Source Stability	£ ± 0.05 % with Oriel QTH Standard lamp or spot QTH
Current accuracy	± 0.01% @ 6.500 Amps ± 0.00065 Amps @ 6.500 Amps (at 23° ±1°)
Current Stability	± 0.001%, ± 10 ppm (after 20m)
Maximum fluctuation for which the current accuracy is maintained	± 10% in line voltage and load voltage
Line regulation	£ 2 ppm/V
Spectral irradiance uncertainty due to error in setting current	0.04% @550 nm
Temperature range for which the accuracy is maintained	0°- 45°C

Parameter	Description
Instrument	Variable Low-Light-Level Integrating Sphere Calibration Standard
Sphere and Optical Bench Manufacturer	Thermo Oriel, Stratford, (CT) USA
Sphere Diameter	8 inches uniform integrating sphere
Sphere Coating	Barium Sulphate
Exit Port Diameter	2 inches
Radiance uniformity	<± 0.2 % over the exit port at 1 m
Source Stability	<± 0.05 % with Oriel QTH Standard lamp or Philips QTH lamp and Optronic OL65-A radiometric power supply
Current accuracy (OL65-A)	± 0.01% @ 6.500 Amps (at 23° ±1°)
Current Stability (OL65-A)	± 0.001% (after 20 min)
Fixed Aperture Wheel	approximate relative radiance 0.9:11:52:100:340
Variable Aperture	radiance range 1:45
Input Irradiance Range	1 to 1000 changing distance and source
Total radiance range	1 to 10¹⁰
Calibration accuracy of fixed aperture ratios	0.2% (nominal)
Minimum luminance	~0.00002 cd/m² (nominal)
Shutter	open / close for background light determination
Light Sources	200 W Oriel QTH Irradiance Standard; Osram QTH lamps; Philips SON 70W; Philips HPL-N 80W
Color Temperature Range	2500 - 3000 K

Parameter

Description

Instrument	Portable Spectral Radiance Standard
Manufacturer	Gigahertz-Optik, Puchheim, Germany Serial No. 3634aw
Sphere Diameter	2 inches uniform integrating sphere
Sphere and baffle coating	OP.DI.MA. 15/10 (reflectance 98%)
Exit Port Diameter	20 mm
Radiance uniformity	<± 1.5 % over the exit port at 1 m
Light Source	QTH tungsten halogen lamp
Radiometric Power Supply	LCRT-2000 current controlled with ramp function
Current accuracy/stability	0.25% /°K (from 23° ±1°)
Maximum current fluctuation	170-264 VAC/47-63 Hz
Spectral calibration range	380 to 1100 nm
Spectral radiance uncertainty relative to NIST	±6% from 380 to 780 nm ±8% from 790 to 1100 nm
Radiance uniformity	±1.5%
Spectral radiance uncertainty due to ±0.25% uncertainty in lamp current	±2.3% @ 300 nm (for tungsten lamp @ ~3000K) ±1.0% @ 550 nm ±0.5% @ 1000nm
Radiance stability	1% @ 550 nm after 30 min (not including the aging effect of the lamp)
Expected repeatability	1% @ 550 nm
Color Temperature	2713 K
Typical spectral Radiance and luminance	238.9 mW m^-2 nm^-1 sr^-1 @550 nm 19323 cd/ m²Photopic 25996 cd/ m²Scotopic

Parameter	Description
Standard source	The Moon
Photometric stability	1% in 10⁹ years
Irradiance uncertainty relative to NIST	~5%
Typical illuminance	10 – 300 mlx
Spectral Response	Solar spectra (in the visible)
Apparent size	<30”
Main phenomena to be accounted for	Geometry of illumination and observation, atmospheric extinction, libration

The radiance standard with optical bench, baffles and target

The Variable Low-Light-Level Calibration Standard in one of its configurations

Detail of the integrating sphere (left) - One of the lamps (right)

The Portable Spectral Radiance Standard with the integrating sphere and the radiometric power supply (left) - The Moon in the visual field of a luminance meter (right)

Wavelength calibration

Instrument: Portable Hg-Ar wavelength standard

Description: Low intensity Mercury-Argon portable lamp for wavelength calibration with fiber optic cable

Parameter	Description
Manufacturer	StellarNet, USA
Source	Hg-Ar lamp
Calibration wavelength range	253.65 nm – 1013.98 nm
Exit port	SMA905 connector + Fiber Optic cable
Power Supply	9V alkaline battery

Spectral responsivity calibration

Instrument: Low-Light-Level spectral responsivity calibration standard

Description: The Low-Light-Level s pectral responsivity calibration standard has been set up for testing photometers and radiometers made for low light levels. The device consists of an in-line Fastie-Ebert monochromator with the entrance slit illuminated by a Spectral Irradiance Standard source through a large collector lens. A removable longpass filter allows to eliminate the contribute of the second order spectra at larger wavelengths. A lens at the exit slit illuminates the detector under test or produces a collimated beam which a radiometer sees as a source at infinity. A shutter allows to properly measuring the stray light from background room light. A high performance radiometric power supply provides that lamp current uncertainty is a only a very minor source of measurement uncertainty. Black low reflectance fabric and baffles help to reduce unwanted reflections. The monochromator efficiency depends on the wavelength, so the responsivity curve is obtained comparing the relative intensities measured by the detector under test and by a reference detector. At the moment we haven't strict requirements on accuracy because we are mainly interested to check the spectral response of our instruments rather than obtain an accurate responsivity calibration. So we use for comparison a detector with known response rather than a certified spectral responsivity standard. As an indication, the apparent photopic luminances measured by a luminance meter with 1 degree field of view at a distance of about 1 m with 600 µ slits range from 4 10³ cd/m² at 550 nm, to about 10³ cd/m² at 650 nm and 500 nm, to few cd/m² at 400 nm and 700 nm. Given that typically our instruments measure under 10^-3 cd/m², we can measure the responsivity curve over 6 decades. In the same configuration the measured photopic illuminance is 1 lx at 550 nm which can be increased reducing the diameter of the lighted spot.

Parameter	Description
Instrument	Low-Light-Level spectral responsivity calibration standard
Monochromator	in-line Fastie-Ebert design
Monochrom. manufacturer	Optometrics USA Inc., Ayer, MA/USA
Range	200 - 880 nm (300-800 nm nominal)
Effective Aperture	f3.9
Focal length	74 mm
Grating	2x2 cm, 1800 l/mm hologr., 500 nm blaze
Linear dispersion	7.21 nm/mm at 500 nm
Resolution	4.32 nm at 500 nm with 600 μ slits (4.4-3.6 nm from 200 to 800 nm) 2.16 nm at 500 nm with 300 μ slits
Wavelength accuracy	±0.2%
Reproducibility	±0.2%
Wavelength readability	0.2 nm
Stability	±0.02 nm/C typical
Stray light	<0.003%
Second order radiation	lambda/2 radiation blocked in 530-880 nm range with Schott GG475 filter
Operating temperature	-20 C to +80 C
Collector lens	f3.5 F= 235mm
Spectral standard source	Philips QTH lamp and Optronic OL65-A radiometric power supply (see above)
Objective lens	f1.8 F=50 mm
Apparent luminance measured at 1 m with 1° field of view and 600 μ slits	1 cd/m2 at 400 nm, 21cd/m2 at 450 nm, 1067 cd/m2 at 500 nm, 4100 cd/m2 at 550 nm, 2973 cd/m2 at 600 nm, 910 cd/m2 at 650 nm, 3 cd/m2 at 700 nm
Measured illuminance at 1 m with 600 μ slits	0.2 mlx at 400 nm, 0.5 mlx at 450 nm, 0.26 lx at 500 nm, 1 lx at 550 nm, 0.7 lx at 600 nm, 0.2 lx at 650 nm, 0.7 mlx at 700 nm
Responsivity standard	None available. We use silicon detectors with known response for instrument tests

The optical bench without baffles (left) and the monochromator (right)

Reflectance standard

Instruments: Labsphere Spectralon Reflectance Standard

Description: Spectralon diffuse reflectance standard offer the highest diffuse reflectance values of any known substance, with typical reflectance of 95% to 99% spectrally flat to +/- 4% over the range of 250 to 2500 nm and +/- 1% over the photopic region of the spectrum. Spectralon also is the most lambertian reflector available for use over the wavelength range from 250 - 2500 nm. Each target is supplied with diffuse reflectance data from 250mm to 2500mm, in 50 mm increments, calibrated and traceable to The National Institute of Standards and Technology (NIST).

Parameter	Description
Standard	Spectralon 99% White Reflectance Standard
Manufacturer	Labsphere Inc., North Sutton (NH) USA Serial number: 38586-I-I
8° Hemispherical reflectance	99 % from 350 to 1300 nm 95 % from 250 to 2100 nm
R(0°/45°) Bidirectional Reflectance	1.021 @550 nm
Calibration uncertainty	< 0.5 % from 300 to 2200 nm < 2 % from 250 to 2500 nm
Target reflectance uncertainty	±1% 400 nm - 990 nm
Material	Washable thermoplastic resin
Size	12.7 cm x 12.7 cm square plate

Acknowledgments

The ISTIL LPLAB’s instrumentation set up has been supported by the Italian Space Agency contract I/R/160/02, by Pierantonio Cinzano and by the International Dark-Sky Association, Tucson. The WASBAM tripode was kindly provided by Auriga Srl, Milano, the device for polarization measurements was funded by the Associazione Friulana di Astronomia e Meteorologia, Remanzacco and the Fastie-Ebert Monochromator was funded by the British Astronomical Association Campaign for Dark Skies.

References

Cinzano, P. 2003, The Laboratory of Photometry and Radiometry of Light Pollution (LPLAB), ISTIL Int. Rep., 7, Thiene, Italy

Cinzano, P., Falchi F. 2003, A portable wide-field instrument for mapping night sky brightness automatically, Mem. Soc. Astron. It., 74, 458-459

Cinzano, P. 2002, WASBAM Manuale di Procedura, ISTIL Int. Rep., 1, Thiene, Italy

Cinzano, P. 2002, Reduction Procedure for WASBAM Data, ISTIL Int. Rep., 2, Thiene, Italy

Cinzano, P. 2003, A laboratory of photometry and radiometry of light pollution, Mem. Soc. Astron. It. Suppl., 3, 312-315

Cinzano, P. 2003, A laboratory for the photometry and radiometry of light pollution, poster presented at the meeting of the Working Group "Light Pollution" of the International Astronomical Union, XXV General Assembly, Sidney 22 July 2003.

Cinzano, P. 2003, Working Procedure to Reducing WASBAM-SSH Spectra with IRAF, ISTIL Int. Rep., 4, Thiene, Italy

Cinzano, P. 2003, Characterization of the Variable Low-Light-Level Calibration Standard, ISTIL Int. Rep., 3, Thiene, Italy

Cinzano, P. 2003, The WASBAM-SSH Spectrophotometer - User Manual, ISTIL Int. Rep., 5, Thiene, Italy

Cinzano, P. 2003, The ISTIL/LPLAB Irradiance and Radiance Standard, ISTIL Int. Rep., 6, Thiene, Italy

Cinzano, P. 2004, A portable spectrophotometer for light pollution measurements, Mem. Soc. Astron. It. Suppl., in press (poster presented at the XL Nat. Meeting of Soc. Astron. It.)

Our main papers are available from www.lightpollution.it/cinzano/papers.html

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