A Valve engineer fixed 3D lighting so hard he had to tell all the graphics card manufacturers their math was wrong, and the reaction was: 'I hate you'

....ish

The maths was right, except it was all being done on colour values than already had the CRTs response curve baked into them. You may have heard of "gamma correction". Well, this is when you correct an images colour values for the display you'll view it on.

Blending before gamma correction and after gamma correction produce very different results. The cards were doing it after. This story is about doing it before.

Paul Debevec had similar observations around the same time. His work at the time was all about HDRI and that was put into Source a few years later.