First of all, let me say that english is not my first language, so please excuse any mistakes that you could meet from here on out.

I read several articles and explanations about luminance and illuminance, I have almost understood what is the difference between them but I'm still a little confused and that's the reason why i'm writing here.

Avoiding the technical definitions, I understood that Illuminance is the amount of light perceived on a surface, while Luminance, then, is how much reflected light is perceived looking at that surface.

The question is: can I consider the light reflected like a form of illuminance?

For example: consider a subject, a female/male portrait on a white background, there are not light sources in this subject but sources of light are behind my back and bring light to my subject. I take a photo of this subject with my camera. What my eyes as well as the sensor of my camera perceive is only light reflected from the subject....uhhmmm...light reflected? I could say that what I catch with my eyes and with my camera is Luminance...or Illuminance? I mean, yes, light is reflected from the subject but then reflected rays of light become incident rays of light for my eyes and for the sensor of my camera...don't you agree?

Hoping my question is clear, if it's not clear just tell me, I will try to explain myself better.


1 Answer 1


It is correct to consider the light reflected a form of illuminance, but the term is usually used in the context of how much light energy is falling on a sensor in Lux, lumens or foot candles.

Luminance is a measure of the intensity of something that is a brightness component of a scene. Another way to look at this in real life is the CIELAB color space. Where L* is the Luminance component of the metric for color description. Luminance is commonly used to characterize emission or reflection from flat, diffuse surfaces. So it may not have a practical application related to your description of it's use, but this should at least clear that up.

  • 1
    thanks mate, I don't understant why my question was labelled "duplicate", I mean, yes, I speak of an argument that is already treated here on photo.stackexchange, but my question was more particular... Anyway, thank you for your reply, it helped me.
    – marco
    Apr 5, 2014 at 11:19
  • Agreed, looks like a different answer and question Apr 5, 2014 at 12:07

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