Re: blackbody and daylight functions

Thiago Ize

Blackbody works only for incandescent lights. Make it 20000K and it should look like what you posted (blue with hints of red). It'll still have red in it because all that changed from the hotter light is that correspondingly more blue was added, but red was never removed. This is why you can't get a pure blue. What you can do is drown out the red by having huge amounts of blue. Even hotter temps will emit lots of UV, but since we don't see that we'll just see it as more blue. Also, that's a crazy hot surface and probably not realistic...

In the real world filters would be applied to incandescent lights to filter out the red so we see it as more blue. Or LEDs or other non-incandescent lights are used which can generate specific frequencies of light.

Take a look at the graph in which shows how at 700nm the blue star is still outputting more red than the red star.

To summarize, blackbody for lights is for incandescent lights without filters. Anything else and the renderer should allow users to input colors in some other fashion, such as RGB.

On Mon, Jan 11, 2021 at 12:16 PM <chrisbrejon@...> wrote:
Totally ! ;-)

Our studio is following the same path most studios are : we have an Hosek sky implementation since 2015 (if I recall correctly).
And we are indeed looking at Sebastien Hilaire's work for our next generation Skylight.

Sorry for repeating myself but my question was really about the temperature function for, let's say, an area light.
An artist may think : let's use a kelvin temperature of 20 000 to get a blue sky color on a rim. And because most render engines
rely on black body tables, the blue color will actually look quite purple (to me). Hence my question...

Of course, we would not want a "flat" color on a EnvLight but on an area or spot light to simulate a rim or a top light. A bit like this :

I guess my point is : in many renderer's documentation, you may read that black body temperatures above 15 000 would give you a sky blue color...
When actually it is not really a goof fit imo.

Sorry for the confusion, I don't mean to bother you guys. ;-)
Once again, your answers are much appreciated !


Join to automatically receive all group messages.