[Radiance-general] splitting a render by light sources - rtcontrib

[Thomas Bleicher]

On 29.01.2006, at 20:11, william reynolds wrote:

> having said that, i dont really follow waht you mean by
> "set the cut-off past the natural cut- off of the fixture".
> could you explain a bit more please.
>
> thanks once again
> will

Greg just pointed out that the spotlight is an unnatural light
source with an unrealistically sharp edge you won't find in any
physical fixture. So you should not use a spotlight if you want
to create a downlight in your scene and get realistic results.

You can modify the output distribution (and with this the "edge"
of the beam) of a spotlight with measured data and get a better
representation of a real world fixture. But you have to use a
spotlight angle that exceeds the angle of the fixture the data
was taken from or anything beyond the angle of the spotlight
will just be black.

Example: If your data shows a beam angle of 30 deg for the
fixture use an angle of more than 30 deg for the spotlight (add
5 or 10 deg to be sure you won't cut of small amounts of light
at the rim).


hth,

Thomas