Should I use Corona Light material or Self Illumination to illuminate my scene?


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 source of strong light in your scene. That is for example: lamps, cove lights, candles - light sources that cast shadows and illuminate objects.
  • Self illumination in Corona 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?


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 objects. 



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 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 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)

Incorrect setup. Rendering is fast but intensive light is clamped by MSI, which produces wrong results.



D

City lights - self illumination

UFO light - self illumination

32 passes

Rendering time: 23s

Rays/s: 5,699,721

MSI=0 (unbiased mode)

Incorrect setup. Intensive light with self illumination is not clamped but produces heavy noise.