Making a Lumens patch

Maybe you would want to check the way I added physical units in BlendLuxCore, or for Cycles/EEVEE in the Photographer add-on.
There is an option per-light to do the lumen-to-watts conversion using color luminance or not.

Lumen is the first step, but I hope you will consider adding the other units in the future as lumens only make sense for point lights.

2 Likes

Hi! Sorry for the bump. Looks like I arrived very late at the discussion… but I think it’s a pity that this patch gets lost in oblivion.
I think that having lumens available will be very useful for many people.
I understand the Lumen vs irradiance variation with light color, but I think that taking that into account in Blender will be overkill for most practical purposes, and if that keeps the lumen away from the Units system I vote to drop it right away.
Lumens will be used by people trying to match or reproduce real world light sources, and most real world lamps colors will lie roughly between 3200 and 6500 K, so I think that a standarized conversion normalized at 6500 Kelvin (D65) will be enough for most practical applications. The difference in Lumen multiplier between 3200 and 6500 will be very small.
Also, in most real world situations, a blue light will be a D65 source with a blue gel, so the the lumen spec for the lamp will still be the standard for D65.
People needing to calculate the REAL lumens of a deep blue light can do the math with the help of a table in the manual, but for most practical uses One Lumen to Rule Them All will be enough, and very useful. Also, all real-world hue-varying sources (like RGB leds) doesn’t crank the intensity up as they approach blue to compensate for the loss of perceived intensity either.
Sorry for the intromission and thanks to all the devs that worked in this!

2 Likes