Photometry is the science of measurement of light.

• Luminance is the luminous intensity of a surface in the direction of the observer. It measures the light as perceived by the human eye.
  Luminance is measured in candela per square metre (cd/m²) (or candela per square foot).
• Illuminance is the luminous flux measured on the surface receiving the light. Its unit of measurement is the lux or footcandle.

Consequently, a white surface and a dark surface lit by the same source have the same illuminance, but not the same luminance!

For photometric studies, we recommend measuring the luminance, in candela per square meter, since that is what the human eye perceives.

Superior photometric performance

Schréder luminaires deliver long term superior photometric performance. Schréder offers a great variety of high performance reflectors adapted to the light source and the area to be lit.
At R-Tech, the Schréder Group’s laboratory and R&D center, photometric performance levels are checked systematically. Numerous measurements are taken of luminous flux distribution, in order to constantly improve the performance levels of the reflectors. A goniophotometer responding to the latest requirements enables the photometric performance of luminaires to be optimized during development.

Real reflective characteristics of the surface to be lit

Because of the difference between luminance and illuminance, it is important to know the reflection characteristics of the surface to be lit. The more light is reflected by the surface, the smaller the light source needed to obtain the requested luminance levels.

To take the surface’s reflection characteristics into account in order to find the right light, Schréder developed the Memphis, the portable surface reflectometer. This major innovation enables an increased number of on-site measurements. The optoelectronic technique is non-destructive, fast and therefore more economical. Only 5 minutes are needed to record the characteristics of a road sample. By using the instrument, the error rate for surface reflection measurement has fallen from 100% to only 15%. The increased number of measurements ultimately provides us with a more precise image of the reflective characteristics of the surface to be lit.

Memphis is a measurement tool that helps defining the exact quantity of light to be used, according to the road surface, for the “right light”.