How can you have a scene linear reflectance greater than 100%?

Started 3 months ago | Questions thread
alanr0 Senior Member • Posts: 2,484
Inverse square law

Mandem wrote:

I was looking at the curve of SLOG3 but didn't understand how light can be reflected more than a 100%? This indicates to me that 100% reflectance isn't really 100% and that instead it's in relation to some standard. Consequently, this would indicate that 18% gray reflectance isn't reflecting 18% of all light either. Could someone please explain what exactly is happening here? Thanks.

Mark, J A C S, Tom and Jim all make valid points.

Further to Mark's post it is not even necessary for a source of light to be in frame. It can simply be out of frame and off to one side.

You can have an ideal diffuse Lambertian surface, which reflects 100% of the incident light, and scatters it according to the Lambertian cosine rule. When illuminated by a distant light source, such as the sun, you will detect the same luminance from each part of the surface. It all appears uniformly bright.

When the illumination is oblique and from a nearby source, the illuminance (lumens per square metre) is higher for those parts of the surface which are closest to the source. These parts appear brighter because they are reflecting 100% of a high illuminance, while the more distant parts of the scene are reflecting 100% of a lower irradiance.

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Alan Robinson

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