While trying to figure out some really subtle stuff with image based lights, I was having big problems trying to see what was going on. So I thought if I could make a way to render an object showing different color bands representing the strength of the light, it would be really useful.

This is the result. The image shows my light meter material. It produces 8 color bands.

Black - no light reaching here at all
Red - very very dark (up to 1/6th of maximum)
Orange - very dark (1/6th to 2/6th)
Yellow - dark (2/6th to 3/6th)
Green - medium (3/6th to 4/6th)
Blue - light (4 to 5 6ths)
Violet - bright (5 to 6 6ths)
White - Overexposed - whiter than white

To use it, just attach to any object, like a sphere. This version is set up to show you the amount of light using the standard diffuse node. You can replace that with any of the lighting nodes and it will show you what is going on really well.

I'll be posting more stuff after this message, including the material file. I'd post the object I use as well but it is too big to post in the forums. If somebody wants to host the object, I'd be happy to send it. However, you can use any object at all - just attach my material to it and you are good to go.

The image here uses a point light in the center of the light meter object. Of course you can use any other lights as well, which is the whole point.

I've learned some very interesting things about IBL and the shader nodes using this device.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)