Light reflectance values for ceilings
In order to get the best efficiency, both for incident daylight and lighting, the ceiling's light reflectance should be high. The main reasons for this are:
- Room perception
A bright ceiling with a high Light Reflectance Value will remind of outdoor conditions at daytime, when the sky is often the brightest surface. In general, this tends to make the room look bigger, since high ceilings are associated with bright rooms thanks to generous daylight intakes through the façade. On the opposite, a dark ceiling evokes a room with low height. Low ceilings mean reduced façade surface area and limited daylight intakes.
- Energy efficacy
A ceiling with a high Light Reflectance Value will support the performance of the lighting installation and help to spread light efficiently throughout the room. That way, the lighting installation can be optimized. Or by providing a higher illuminance on working desks (i.e. a larger amount of light on the surfaces meant to be illuminated in the room) for a given effect. Either by installing a lower effect than would have been the case with a ceiling showing a lower light reflectance value. The latter should be preferred, as it leads to reduced energy consumption.
- Glare reduction
To a certain extent, high ceiling light reflectance reduces the risk of glare from light fittings, by reducing the luminance ratio, which is the difference in brightness between the light fittings' luminous surfaces and the surrounding ceiling. In the case of direct lighting the suspended ceiling's light reflectance should be at least 70%.
Indirect lighting, i.e. light projection towards the ceiling surface, requires high light reflectance. The level of illumination in the room will depend directly on how much light the ceiling surface reflects, starting from the very first reflection. In a way, every % less in Light Reflectance Value has an impact of the same magnitude on the efficacy of the lighting system. The Light Reflectance Value of the ceiling should be at least 80%.
Finally, a high Light Reflectance Value will lead to a more even spread of light throughout the room, assumed that the walls are also reflective. One can say that thanks to a reflective ceiling, light gets a chance to bounce a few more times before it is absorbed by the room surfaces.
Light Reflectance Value is measured in accordance with the BS8493:2008+A1:2010. Measurement values are evaluated with CIE 10 degree Standard Observer (1964) and CIE Standard Illuminant D65.