Maximum-Dev
November 26, 2018, 11:19pm
215
rosegoldslugs:
.sch documented a good method a few pages back, which is similar to what I do at work as well. Essentially, you can do it from a sphere(easy to sample from any direction) or use a plane oriented towards any particular direction you want to measure. The material on either mesh needs to be pure white(1.0, not PBR white) and fully rough. If you lay the plane flat, horizontally, you’re recreating a horizontally placed light meter, which is usually the case since IRL you don’t really want to burn out the meter by pointing it directly at the sun.
With the Pixel Inspector enabled, and you’re in game mode(nothing will happen if you’re not), you can sample an area on the mesh. For the sphere, it’s most likely the direction of the dominant light source or the top pole. For the plane, it’s anywhere on the top face. It’s a good idea to disable bloom, fog, DFAO/SSAO, and any other post-effect that might interfere with the scene color. The HDR input in the Pixel Inspector measures everything in luminance or cd/m² or nits, which is why you want to use a pure white material since luminance is based on color. Taking that HDR value and multiplying it by pi will give you the Lux value.
Lux is easier to find for any given lighting condition. Luminance is a good measurement if you’re really trying to nail a sky material or emissive surface. With most Lux measurements online, they will include the sky contribution too. I will usually measure the skylight by itself and then the sky and sun to get the ambient in range first before the sun, since the sun measurement on a Lux meter can vary drastically based on the angle of the sun and card.
Thanks for the explanation. I do still find it darker than expected though.
I’ve adjusted the sky dome brightness until skylight at 1 intensity gives me an HDR value of around 7960 which results in 25,000 Lux after multiplying by 3.14.
Then added directional light on top of that, with 100,000 Lux which results in HDR value of around 40,000 which results in around 125,000 Lux after multiplying by 3.14.
Here is what I get:
Here’s what I expect to get:
There’s a very large difference in both pictures and I still fail to see why. Also consider the fact that my light source is facing down, it goes darker with a 45 degree angle.
