Why is there such a diff between "Self Illumination" and "Rectangular Light"?

Note the differences in

  • Graininess
  • Bounced Light (floor & posts)
  • Overall Brightness (both are white/100%)
  • Color

Below at 250 samples

Below at 1000 samples

I’d half-way expect the results to be somewhat similar, minus the fact that the light-emitting surface also throws light UP the z axis. I think this is a good testement to how well Cycles handles light-emitting surfaces (or how well @nathanletwory has tied it together).

=== Notes regarding Cycles light-emitting surfaces ===
Any chance we will get the ability to BUMP UP the amount light emitted from a surface? Right now it seems slightly less than a regular light, and I would expect to either see an rough equality (when light is white @ 100% and material is white), or the ability to increase the light emitted from the material.

In my mind “Self Illumination” is actually a hack. What it means is that ANYWHERE on the object, the amount of light you see is more than the sensor of the camera can handle, and thus is ‘blown out’ or overexposed. In real life we can have multiple objects which are “overexposed” at any given exposure level, but actually emit various levels of light, or just happen to reflect enough to overexpose the camera.

With an unbiased renderer like Cycles, I think all objects “Emit” light (bounce or originate) by default. It looks like we need a way to tell cycles that we want an object to “add light in addition to bounces”. Right now the ‘Self Illumination’ toggle does that, but in a way that is not very controllable. What if it’s a 1 Watt LED chip? What if it’s the 1000 Watt led chip? What if we want it to emit a very low amount of light AND see shading on it? (Picture a florescent tube outside during an overcast day)

I think the simplest way to do this in the existing GUI would be to use the “Emission” color picker. I know it’s not quite as intuitive as just the ‘Self Illumination’ toggle, and in reality perhaps it should be an ‘Emission Strength’ number (Lumans?) which would use the already-defined material color, but it would at least give us the ability to control the amount of light emitted without overexposing a surface.

Am I way off base? Is there an easier way to tell Cycles “Make this material also EMIT light of X strength and X color”?

Just my two cents. :slight_smile:

@nates, add the Cycles Emissive material to an object. This gives you much better control over strength and fall-off mode. It then adheres to the light formulas as per Cycles manual. I am currently on vacation, I don’t remember the exact values for i.e. falloff. Strength you can set as high as you want, or even negative for funky effects.

Another way is to change the light factors in the advanced section. Type RhinoCycles and look for keys with light in the name. You’ll see what I mean. Note though that these settings will affect any subsequently started Raytraced render.

Self-illumination is a misnomer, btw. It really means shadeless, and this shouldn’t light other objects, at least not as a light. That should be considered a bug.

Aha, that material is a little more controllable! Thanks Nathan, and enjoy your vacation!

You can also use GrassHopper to control the emissive amount (and color) with sliders :slight_smile: