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How do I make an object visible based on the light it’s recieving
So I have a car that isn’t lighting up properly, despite being directly beneath a spotlight, due to the fact that (as I’ve been told) the scene is too dark for the car to reflect anything. I added a sphere around the car, added a luminance map to the sphere and set it just enough so we can see the color of the car without it being too bright to compromise the spotlight’s intensity. That worked nicely, but that also meant that it is no longer affected by the spotlight, so can I somehow make the sphere only appear in the light? A way I thought of doing this is to link the transparency (of the sphere’s material) to be relative to the amount of light hitting the sphere but I don’t know how to do that.
If you have any easier suggestions for what I want to do, please let me know.
Thanks
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2 Replies
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use a Sky object rather than a sphere around the car (with the same material you added to the sphere)
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Or you can use a compositing tag and tell the sphere to not show in the camera and to not cast shadows (is it blocking the light perhaps – make the sphere really really big). You can also exclude the sphere from the main light’s project tab so it doesn’t blow out the luma map.
If you can use an HDRI texture in the sphere’s luma channel (assuming a Global Illumination (GI) render) that will give you a better reflection than a standard 8 bit image (often you have to mix down the luma channel’s image with a standard black luma color so the HDRI doesn’t light the scene like a thousand suns)
But if you go the GI route, the addition of the overhead light is almost swimming against the current. With GI, the scene is getting its light and shadows from the texture in the sphere’s luma map. If you need to art direct lighting, its often better to add a disk object and add an hdri map that is a basic circular or square radiating gradient to the luma map for the disk and move that around in the scene like a bounce reflector on a photo shoot. That disk “becomes” a light.
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