Raytracing and Skylight

[anonymous_user_b9774f68]

Hi all
I am a beginner.
I wanted to ask if, with raytracing enabled, I need a skylight in my lanscape scene and if so, what the benefits of it are. Isn’t the raytracing doing the work of the skylight?
I am using a direct light, a sky atmosphere, volumetric clouds and exponential height fog.
Many thanks

[Arkiras]

Yes you need a skylight

Isn’t the raytracing doing the work of the skylight?

No

[anonymous_user_b9774f68]

@Arkiras

Yes you need a skylight

No

Hi @Arkiras
First and foremost thanks for helping.
I got an additional question if you don’t mind: if raytracing calculates global illumination and reflections/refractions in the scene, then what is the goal of the skylight?
On the documentation skylight is described as such:* "The Sky Light captures the distant parts of your level and applies that to the scene as a light. "*
But isn’t this indirect lighting? Shouldn’t the scene contribution be calculated by the raytracing?

Thanks
P

[Bits360]

@anonymous_user_b9774f68

Hi @Arkiras
First and foremost thanks for helping.
I got an additional question if you don’t mind: if raytracing calculates global illumination and reflections/refractions in the scene, then what is the goal of the skylight?
On the documentation skylight is described as such:* "The Sky Light captures the distant parts of your level and applies that to the scene as a light. "*
But isn’t this indirect lighting? Shouldn’t the scene contribution be calculated by the raytracing?

Thanks
P

Indirect lighting is not a suitable replacement, or even remotely related to the skylight. Skylight is effectively a requirement. Read the docs. Unreal Engine 5.3 Documentation | Unreal Engine 5.3 Documentation

[Arkiras]

Raytraced global illumination approximates light scattered by reflecting off of opaque surfaces

Skylights approximate light from the sun scattered by particulate in the planets atmosphere.

Conceptually you could think of them both as types of indirect lighting but as engine features as far as I know skylights are only considered “indirect” from the standpoint of shadow casting.

[anonymous_user_b9774f68]

@Bits360

Indirect lighting is not a suitable replacement, or even remotely related to the skylight. Skylight is effectively a requirement. Read the docs. Unreal Engine 5.3 Documentation | Unreal Engine 5.3 Documentation

thanks for the message @Bits360 .
I see, so I guess in Unreal they are 2 separate things.
I usually do concepts and renders in Arnold, and in it they are instead very related. HDRIs/ambient lighting is usually considered indirect light. So in physics and in painting theory. From this my confusion.
I did go through the skylight page and ray tracing pages of course before asking my question, but I had doubts on their content, so I came here.
A link to the full documentation is, I am afraid, not very useful. But I get your point.

[anonymous_user_b9774f68]

@Arkiras

Raytraced global illumination approximates light scattered by reflecting off of opaque surfaces

Skylights approximate light from the sun scattered by particulate in the planets atmosphere.

Conceptually you could think of them both as types of indirect lighting but as engine features as far as I know skylights are only considered “indirect” from the standpoint of shadow casting.

That was exactly my doubt! In painting theory skylight is usually considered indirect light that has bounced in the atmosphere multiple times so I was a bit confused.
If i got it correctly then, in unreal ray tracing only takes care of bounces from actual geometry.
Thanks for helping me understand @Arkiras
you have been very clear and helpful!