Reflectance — How Your Surfaces Shape Your Light

Reflectance is the percentage of incident light that a surface bounces back into a space. It is a property of every material, every finish, and every colour in your project — and it is one of the most consistently underestimated factors in lighting design.

The numbers are significant. A white or near-white ceiling typically reflects 70 to 90% of the light it receives. A mid-grey wall reflects around 40 to 50%. A dark hardwood floor may reflect as little as 8 to 12%. A matte black surface can absorb over 95% of incident light.

These are not aesthetic footnotes. They are performance variables.

In practical terms, a room with light walls, a white ceiling, and a pale floor can achieve target lux levels at the working plane with significantly fewer luminaires than a room with equivalent dimensions but dark finishes. Depending on the contrast in reflectance values, the difference in required fixture count can be 40 to 60 percent. That translates directly into installation cost, energy consumption, and the ongoing maintenance load of the building.

For lighting designers, reflectance values for all major surfaces must be part of every calculation input. Most calculation software — DIALux, Relux — includes reflectance as a room parameter precisely because the result is meaningless without it.

For interior designers, this is the argument for treating the lighting brief and the finish schedule as a single document. When a client falls in love with a dark palette, the correct response is not to push back on the aesthetic. It is to quantify what that palette costs in additional fixtures, energy, and maintenance — and to design a lighting scheme that works within it rather than one that assumes light surfaces that do not exist.

Every surface is either working with your light or working against it. Know which before you finalise either.

Every surface in your space is either working with your light or working against it.