View Full Version : How to get info about light intensity

09-08-2014, 11:05 AM
Hi guys, I am working currently on some animation about controlling lighting in spaces like offices, halls, storages etc., depending on intensity of outdoor lighting during daytime.
It is possible to get the info about intensity of the lighting at a given point in the scene ?
Any Idea ?

09-08-2014, 11:13 AM
Light info node will give you the intensity of a singe selected light... to get full scene lighting info you'd have to get the intensities of all lights in your scene.

09-08-2014, 11:33 AM
Although this book is obviously about photography, I think it might be helpful to people learning about lighting in general. It helped me at least. :)


09-08-2014, 03:35 PM
So, no "LightMeter" node yet, eh? :(

09-08-2014, 05:25 PM
So, no "LightMeter" node yet, eh? :(

I thought this was the kind of thing "Lightbitch" was doing? Never used it, so don't know. Is it just for HDRI's?

09-09-2014, 02:49 AM
Light info node will give you the intensity of a singe selected light... to get full scene lighting info you'd have to get the intensities of all lights in your scene.

I will try to explain it bit more.
My goal is to show that the lighting control system maintains the amount of light at a given point on the same level as the lighting changes during the day. If there is not enough ambient light, (early morning, late evening, overcast sky, the sun hidden behind the cloud) then the system increase the intensity of the ceiling lights and vice versa.

So, how do I measure the amount of light, which comes only from outdoor lighting, at the marked point in my scene so I can compensate it with my ceiling lights to desired level ?.

My only idea is to change all colors in the scene to white, destaurate Sunsky enviromet to get pure grayscale render and look at the rgb values in that point. If there is less than 255, 255, 255 then I will play with intensity of ceiling lights and do some test renders till it will be pure white. Then import all lights back to fully colored and textured scene with hope that it will works.

09-09-2014, 04:11 AM
Yeah... ok, that's tricky.

If its just for single shots you're wanting, then you approach would work and probably take the least amount of fiddling around. If you're after a dynamic effect for an animated shot... only one way I can think which may or may not work...

Put a nodal filter on your lights intensity channel... In the editor, use a ray trace node to fire a ray from just above the desk to the desk surface. The returned colour value will show you how illuminated it is. Bit of math to figure out from there how much light is "missing", and pump that into the light intensity channel.

I'd guess this may well not work, as there's no way to specifically include only the ambient illumination in that sampling, so at best you might get something weird, at worst, super crazy flicker. I guess in that case, you could sit a "hidden" poly object just above the desk, set it to ignore lights, sample that.

09-09-2014, 04:26 AM
Hmm, I'd try RH's method, but just wondering if you could use a proxy object, a simple box with cutouts to match the area and placement of windows, doors, etc., set it to a simple white surface, and sample that for your brightness, that way there are no feedback loops in your nodal networks.