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Photometric Testing's Laboratory & Equipment


Photometric Testing employs only the latest, state-of-the-art photometric, spectroradiometric and goniophotometric equipment to ensure that our measurements are accurate, repeatable and conform to the latest international lighting standards. Our purpose-designed Cheltenham laboratory comprises a dedicated, 80m² dark room with air conditioning regulated to maintain a constant 25° ± 1°C (as required by IES LM79-08). All surfaces are painted matte black, which together with low reflectance carpetting and a full curtain enclosure promotes the very lowest level of stray light and the highest measurement accuracy. Flexible curtain partitioning creates four measurement bays, while for far-field measurements, the curtains can be removed to create a single measurement area with a working distance of 12m. Not forgetting that we have installed state-of-the-art LED lighting in our laboratory - naturally! Thanks to LightSense ( for supplying our efficient, low glare laboratory ceiling panels.


Integrating Sphere Spectroradiometers

For measurements of total luminous flux (lumens), spectral radiant flux (350-1000nm) as well as chromaticity, correlated colour temperature and colour rendering, we have a family of three Labsphere integrating spheres with sizes of 0.5, 1.0 and 2.0m diameter. These are configured for both 2pi forward flux of downlighters and 4pi total flux measurements of diffused or extended sources in accordance with BS EN 13032-1 and EN13032-4 and IES LM79. The spheres are equipped with high speed array spectroradiometers as recommended for improved accuracy by IES LM79 and CIE 127. An auxiliary correction lamp is fitted to the sphere to ensure that the self absorption errors of the device under test are taken into account. Without this, the sphere would record a luminous flux value many tens of percent lower than the true light output. For calculating source efficiency we have a Yokogawa electrical power meter and power factor analyser.

Update March 2015: With our latest 2m sphere, we are one of the few independent UK test labs with a full size photometer for testing the largest fittings. The bigger the light source you wish to test, the bigger the sphere needs to be if you want accurate results. This is not some "Heath Robinson" home-made contraption, ours is a proper sphere which fully complies with IES LM79-08 and the forthcoming EN13032-4. This way, we can ensure the accuracy of our luminous flux, colour temperature and luminous efficacy measurements on almost any size of light source or luminaire.


Imaging Goniophotometers

For measurements of directional luminance and luminous intensity, we have installed two Radiant Imaging goniophotometers with ProMetric CCD imaging photometer/colorimeters. For luminaires we can compile standard photometric data files in the popular IES (.ies) and EULUMDAT (.ldt) formats. The goniophotometer can record the 2pi (near-field) luminance in cd/m² and (far-field) luminous intensity in cd for displays and light sources ranging in size from 5cm diameter up to 60 x 60cm square or 1.8m long. The maximum DUT load is 25kg. The systems can record directional intensity and luminance as well as total luminous flux (lumens). The variation of chromaticity and correlated colour temperature with angle can also be measured. An integrated spectroradiometer device also allows for precise colour corrected readings and the measurement of colour rendering as a function of angle. For displays, we can calculate the view angle and contrast ratio as a function of angle.

Our goniophotometer systems are near-field devices. Near-field (or imaging) goniophotometers record the 2D luminance from a light source for each angle of azimuth and inclination. Software then extrapolates the near-field luminance to a far-field luminance intensity distribution. The main advantage of this technique over traditional (direct) far-field goniometric measurements is that we don't have to worry about any near-field errors with lensed LED arrays or non-diffused light sources. The photometric distance (distance to the far-field) for such sources is much greater than for diffused light sources and the fixed working distance of many far-field goniophotometers can be insufficient which leads to the intensity being recorded low. The near-field goniophotometric system is immune to such errors.


Spectroradiometers, Photometers & Colorimeters

In addition to our integrating sphere spectroradiometer used for measuring spectral radiant flux in the 350-1000nm band, we own a variety of advanced spectroradiometers for performing measurements of spectral irradiance, spectral radiant intensity and spectral radiance.

Our high speed JETI Specbos array spectroradiometer combines the ability to measure irradiance/illuminance, radiant intensity/luminous intensity and radiance/luminance in the wavelength range from 350-1000nm.

Our scanning double spectroradiometer system is equipped with high sensitivity detectors for wide dynamic range, low stray light measurements of spectral irradiance and intensity spanning the entire 200-1700nm UV-VIS-NIR wavelength range. This is the instrument we use for exacting photobiological safety testing of lamps and lighting in accordance with BS EN 62471 and the Artificial Optical Radiation Hazard Directive.
For flashing light sources, and in particular Visual Alert Devices, our flash photometer can measure effective intensity in accordance with BS EN 54-23.

Our ProMetric CCD imaging photometer/colorimeter can be used to measure the instantaneous spatial (2D) distribution of luminance (and colour) from displays, LED arrays and signs and the illuminance distribution from light sources such as car headlamps, torches and lensed LEDs.

Our Admesy Brontes colorimeter records the luminance from displays and light sources at over 18,000 times per second, allowing it to record source flicker.

Our Konica Minolta LS-100 can be used to measure spot luminance in cd/m² while the CL-200 records illuminance in lux, CIE XYZ tristimulus values, chromaticity and correlated colour temperature.