# How do you set world strength to equal a specific lumen value?

If you go outside on a sunny day, the brightness ranges from about 1,000 lumens in the shade to more than 6,000 lumens on a large stretch of concrete, like a highway. Our eyes are comfortable until we get to around 3,500 lumens.

So in an effort to try to figure out realistic lighting I’d really like to set my world strength to a known lumen value. How can I do that? What even is the unit of measure of the World Surface Strength value?

Like how many lumens is the Nishita Sky Texture at strength 1?

You might wanna take a look here!

Now if only I understood math enough to make use of this information.

This actually confuses me a bit more. Assuming that Nishita sky does a realistic job of simulating a clear sky, I took an indoor scene and lit it with Nishita sky and then used a sun lamp to reproduce similar lighting to figure out how bright the 1 unit of sun within Nishita corresponds to the units of the sun lamp. I came up with about 120, not 1000 as stated on that documentation page. Thinsoldier's Sketchbook 2022 - #5 by thinsoldier

Also exposure can be set in both Film and Color Management. Which one should be used when and why? Why does one default to zero and the other default to one??? The exposure under color management can be adjusted without rerendering so it’s extremely tempting to use that one 100% of the time.

The scene has several emission materials: emission flat texture, emission window texture, cabinet lights.

Though I don’t think the difference is that significant.

Exposure centers at 0 as it can go positive and negative, akin to a real camera’s exposure control, without the physical limit of one. The gamma is likely a multiplier to the gamma curve function.

None of those modifies the scene referred data. They are just tools for quick look development.

I had in fact made several renders comparing sunlamp of different strength.

There are differences to how intensive the indirect is, but if viewed in isolation I don’t think anyone will say: “Hey your sunlamp is 10 times too weak.” The scene is also set in high contrast so the effect is greatly exaggerated. Beside the fact that darker scene has more noise I wouldn’t worry much.

Hello, sorry I didn’t reply, I don’t really know. In this demo file he uses a very small strength and a sun intensity of 1.

I am guessing from looking at the documentation that the world is an emission shader, so according to the documentation Watts/m² (on meshes) but also on meshes…

Strength

``````Strength of the emitted light. For point and area lights, the unit is Watts. For >
materials, a value of 1.0 will ensure that the object in the image has the exact same
color as the Color input, i.e. make it ‘shadeless’.
``````