Surfaces and objects in a space may be considered an extension of the lighting system. If light is not absorbed, it is reflected and transmitted with reduced intensity to other surfaces and objects, where it is absorbed, reflected and transmitted. All surfaces and objects in a space that reflect or transmit light can be considered an extension of the luminaires or, rather, a secondary light source with its own particular and notable characteristics.
Surfaces with lighter finishes have higher reflectances and therefore promote interreflections of light in the space. These interreflections typically have diffuse characteristics as an area light source and are distributed on all surfaces in the space, softening shadows, reducing contrast, increasing uniformity and raising light levels. Using indirect lighting, a wall or ceiling can be the sole source of illumination in the space. As a result, materials, finishes, furniture, etc. are important considerations in lighting design, as lighter finishes can reinforce luminaire output through reflection and darker finishes can negate it through absorption. Room surface finishes, therefore, can play a significant role in maximizing the efficiency of a lighting system because lighter finishes can produce relatively higher light levels and perceptions of brightness. In fact, in an existing space with a large area of dark surfaces can improve light levels and visual comfort almost immediately by simply repainting those surfaces a lighter color to improve reflectance—and thereby improve coefficient of utilization, an expression of efficiency of a luminaire in a given application and an important factor in design light level calculations.
Similarly, consider the height of room partitions in open office plans and similar spaces. Taller partitions provide privacy for occupants. Lower partition heights, however, enhance daylight penetration, uniformity and access to a view, while minimizing shadows.
ASHRAE-recommended surface reflectances. Source: ASHRAE Advanced Energy Design Guides.
OFFICE
Ceiling: 80% or higher (90% if indirect lighting)
Walls: 70% or higher (same for >2.5-ft. vertical partitions)
K-12 SCHOOL
Ceiling: 70% (preferred 80-90%)
Walls: 50%
Floor: 20%
SMALL RETAIL
Ceiling: 80% (80+% if daylight zone)
Wall: 50% (70+% if daylight zone)
Floor: 20%
SMALL HOSPITAL AND HEALTHCARE
Ceiling: 85% (direct lighting) and at least 90% (indirect and/or daylighting)
Walls: 50% (70% for walls adjacent to daylight apertures)
Floor: 20%
WAREHOUSE AND SELF STORAGE
Ceiling: 80%
Walls: 30%
Product/Floor: 20%
