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The measurement of luminaires and displays has traditionally been performed with a goniophotometer which measures the light level from the device under test at one angle of azimuth and elevation at a time. The DUT is mounted on a motorised goniometer stage and a photometer views the light source from a distance. Luminaire manufacturers as well as lighting designers refer to so-called "photometric data" for a light fitting. By this, they mean standardised data files that describe the variation of light from the luminaire as a function of angle. The two most common file formats are IESNA (.ies) and EULUMDAT (.ldt). Lighting designers use these photometric files in conjunction with lighting design software in order to calculate the number and positioning of light fittings necessary to achieve the desired level of illumination in a building or street.

Luminaires have traditionally been measured using an illuminance photometer that measures the light level in lux in the photometric far-field. The far-field is that distance where the light source behaves as if it were a point source of light, hence the need to work at a distance of between 10 and 20 times the size of the luminaire. Measurements are reported in units of candelas; the candela is the unit of luminous intensity and in the far-field, intensity is the product of illuminance and the square of the distance between the light source and photometer.

Not all light fittings require a goniophotometric measurement. For downlighters, or for any luminaire that has a narrow beam angle, there is a simpler solution. The Westboro BP100 is a compact, portable photometric or colorimetric measurement accessory enabling fast and precise beam pattern measurements of directional light sources and fiber optic illuminators. The method uses a diffusely transmitting screen to provide a flat image that can be measured by an imaging photometer or colorimeter.

For measuring the view angle performanc of a display, the Westboro CONOMETER® 80 is the ideal instrument for measuring luminance, contrast, and gamma of emissive displays as a function of viewing angle. Compared with alternative Fourier (conoscopic) lens systems, the Conometer is much more affordable and provides a field of view of 80°.

Far-Field Goniophotometers





Far-Field Goniophotometers        

Our range of far-field goniophotometers are used to measure the luminous intensity (in candelas) from automotive lighting as well as from LEDs and general lighting products. We offer far-field goniometers conforming to the requirements of IES type A, C (both moving detector and moving mirror) and (new as of 2016) a type D system for solid state lighting. Data files include IES and LDT (EULUMDAT) formats for lighting design.

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