You’re Probably Lighting Wrong: Physically Based Lighting in UE5 | Unreal Fest Gold Coast 2024

I feel like this is for short people. All right, so now for the main event.

Okay, everybody, just a little bit about me. I haven't done a slide, but my name is Sean Gobi. I'm a technical artist. I work at Gameloft.

And today we're doing, you're probably lighting wrong. So it is a very click-baity title.

the talk is not going to be about how to light, like three-point lights and whatever.

It's going to talk, go over mainly what Unreal is doing under the hood.

So the first thing we're going to do is what's going on, making sense of exposure and values in Unreal Engine 5.

And once we understand that, we're going to do the physically-based lighting, so approach it through physically-based values, right?

And then we're going to look at the tone mapper. And how, like, Unreal deals with the light, and then it has to present it to us.

And then we're going to look at clouds and fogs, and that's a little bit, you know, can't before the horse, but bear with me.

And then we'll get to do some color grading. And then if we have enough time, we'll do a demo, maybe two demos, all right?

So generally when we light, we want to set up, like with your camera, if any of you here use DSLRs,

you set up your camera and then you have your lights, or technically you have your lights and then your camera.

And then once you've taken your photo, you go into Photoshop or Lightroom, and when you import that raw image, they say, hey, what do you want to do with exposure, light values, and then you do your color grading.

But today what we're going to go through is the lights, because there's a lot to learn about how Unreal deals with their lights.

And then once we understand lights,

we're going to deal with how Unreal uses the camera, and then from that, the tone mapper, and then we'll do some color grading.

So what's going on here? Excuse me. So firstly, we have this scene, and there is no lights.

We have emissive materials, all right? And it's very blobby. We're using Lumen. There won't be any light baking here.

And if we just throw in a directional light, it turns on, it illuminates the place.

And we're like, okay, that's fair enough. You can even see the emissive light is still super bright.

So we went from nothing to a directional light, but our emissive fire is still blown out.

Okay, so the next thing you look at is the directional light, and it has a value of 10 lux.

so what what is 10 lux if

we change that number to a hundred thousand

lux you can see there's

a little bit of a flash and then there's no change

except the emissive fire is more

dim all right so essentially what's happening is unreal has a lot it's childproofed epic is childproofed Unreal Engine, right?

So it always looks good. And there's an eye adaption visualizer, which you should probably turn on all the time.

And if we change it from 100,000 lux to 10 lux,

don't worry, I'm going to talk about lux in a minute, but you can see what's happening is this green bar is showing us that Unreal is adjusting the exposure.

So it always wants to get a perfect exposure.

So essentially, you change it from 100,000 lux to 10 lux, and it's just like, what do you want?

I'm trying to get a good exposure here, right? And this is some of the childproofing.

And once you understand this, you can then kind of go, okay, so there's a lot of childproofing in other places, right?

And also another thing that we need to be aware

of is that we're not simulating our eye, we're simulating a camera, because our our eyes have a greater dynamic range than cameras.

And even if cameras had a really good dynamic range, our monitors don't. So we have to kind of work within that paradigm.

So then, what is lux? Lux, or a luminous flux,

is equal to one lumen per square meter and is the total amount of light that falls onto a surface, everybody.

So then, what is lumen? Lumen is the total amount of light emitted by a source in all directions.

If you're anything like me, you're like, okay, great, I still don't get it. So I made this little graphic.

So lumen is the amount of light coming off of a surface,

and lux is the amount of light that is hitting a surface.