Pro Lite Technology

Luminaire Applications


The measurement of luminaires has traditionally been performed with a goniophotometer which measures the light level from the light fitting at one angle of azimuth and elevation at a time. The device under test is mounted on a motorised goniometer stage and a photometer views the light source from a distance. Click here for details on the goniophotometer systems which Pro-Lite supplies.

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.

There are several, additional metrics used to describe the performance of a luminaire. Luminous flux is the total light output and is reported in units of lumens. If you have a sufficiently large integrating sphere, you can quickly measure the total light output of a light fitting, but a goniophotometer will normally calculate the luminous flux based upon a summation of the directional luminous intensity values integrated over a hemisphere. The light output ratio (LOR) is a measure of the efficiency of the luminaire and is calculated as the ratio of the luminous flux of the luminaire to that of the lamp or lamps installed in the light fitting.

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.

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