This depends on the kind of lighting you want to use. Generally:
- Corona Light material technically does not differ from Corona lights, and just like them, it should be used for objects that will be the main sources of strong light in your scene. That is, for example, lamps, cove lights, candles - light sources that cast shadows and illuminate other objects.
-
Self-illumination in Corona Physical Material or Corona Legacy Material should be used for objects that glow in the dark but do not really illuminate your scene. For example lava, glowing buttons, fireflies. Light emitted by self-illumination will be clamped by MSI.
See:- What is MSI? - 3ds Max
- What is MSI? - C4D
Misuse of Light material and Self-illumination may lead to excessive noise or very high render times because these two kinds of materials are sampled differently. For the Light material, Corona sends special rays to sample it like light. Self-illuminated objects are sampled like any other object.
Below is a simple guide on material usage:
| usage / light type | Corona Light Mtl or Corona Light object | Corona Mtl with Self Illumination |
|
Using as the key light source (casting shadows, illuminating other objects) |
GOOD |
BAD - slow, noisy |
|
Subtle light source (not illuminating other objects) |
NOT RECOMMENDED | GOOD |
|
Dim light on a very big area (one big slightly glowing object or lots of slightly glowing objects) |
BAD - slow | GOOD - if the light is dim |
Examples
1. Key light source
Light Material
16 passes
Corona Material with self-illumination
16 passes
2. Key light and faint light sources
A
City lights - self-illumination
UFO light - Corona Light material
32 passes
Rendering time: 28s
Rays/s: 6,195,195
Correct setup.
B
City lights - Corona Light material
UFO light - Corona Light material
32 passes
Rendering time: 56s
Rays/s: 3,206,471
Incorrect setup. Samples required by the UFO light are "stolen" by light material assigned to the buildings. Rendering is slower and its quality is worse.
C
City lights - self-illumination
UFO light - self-illumination
32 passes
Rendering time: 23s
Rays/s: 5,699,721
MSI=20 (default setting)
D
City lights - self-illumination
UFO light - self-illumination
32 passes
Rendering time: 23s
Rays/s: 5,699,721
MSI=0 (unbiased mode)