Different objects reflect the light in different ways. For example, diffuse surfaces appear the same when viewed from different directions, whereas a mirror looks very different from different points of view!
Reflection factor is a ratio of luminous flux reflected by a body (with or without diffusion) to the flux it receives .i.e.
Reflection factor = luminous flux reflected by a body / luminous flux received by the body
OR
The ratio of the total amount of radiation, as of light, reflected by a surface to the total amount of radiation incident on the surface.
In other words, it is the fraction of radiant energy that is reflected from a surface.
Some symbols used for reflection factor are:
rc= Reflection factor of ceiling.
rw = Reflection factor of parts of the wall between the working surface and the luminaires.
rf= Reflection factor of floor.
Light reflecting factors of commonly used materials:
Material | Reflection Factor (%) |
Aluminum, pure, highly polished | 80 – 87 |
Aluminum, anodised, matt | 80 – 85 |
Aluminum, polished | 65 – 75 |
Aluminum, matt | 55 – 75 |
Aluminum coatings, matt | 55 – 56 |
Chrome, polished | 60 – 70 |
Vitreous Enamel, white | 65 – 75 |
Lacquer, pure white | 80 – 85 |
Copper, highly polished | 70 – 75 |
Nickel, highly polished | 50 – 60 |
Paper, white | 70 – 80 |
Silvered mirror, behind glass | 80 – 88 |
Silver, highly polished | 90 – 92 |
Oak, light polished | 25 – 35 |
Granite | 20 – 25 |
Limestone | 35 – 55 |
Marble, polished | 30 – 70 |
Plaster, light | 40 – 45 |
Plaster, dark | 15 – 25 |
Sandstone | 20 – 40 |
Plywood, rough | 25 – 40 |
Concrete, rough | 20 – 30 |
Brick, red | 10 – 15 |
Paint, white | 75 – 85 |
Paint, medium grey | 25 – 35 |
Paint, dark blue | 15 – 20 |
Paint, light green | 45 – 55 |
Paint, dark green | 15 – 20 |
Paint, light yellow | 60 – 70 |
Paint, brown | 20 – 30 |
Paint, dark red | 15 – 20 |