I build RGB torches and light painting tools for a living (Ants on a Melon), so keep that in mind. None of this is brand specific though. It's how lumens are defined and how sensors behave, and it applies to whatever you're painting with.
People ask me all the time how many lumens our lights are, usually to line them up against a white flashlight they already own. It's a fair question, and the honest answer is that the number can't tell you what you want to know.
Lumens measure your eyes, not your camera
A lumen isn't raw light output. It's output weighted by a curve of how sensitive human vision is to each wavelength, and that curve peaks at green and falls off a cliff at both ends. Green at 555nm counts fully. Deep blue around 450nm counts for roughly 4% of that. Red at 630nm counts for about 27%.
So a 40 lumen blue and a 40 lumen green are nowhere near the same amount of light. The blue is putting out far more energy, it just lands where your eye barely registers it. Your camera doesn't use that curve at all. It has red, green and blue pixels with their own sensitivities, and blue pixels are very happy to soak up 450nm.
Which is why a dim looking RGB light beats a bright white one
White is every wavelength at once, so the camera splits it across all 3 channels and no single one gets much. A saturated color piles nearly all of it into 1 channel instead. Add the eye curve undercounting that color in the first place, and a 40 lumen blue can expose harder in the frame than a 500 lumen white flashlight does.
That's the part that surprises people. For light painting, low measured brightness in a strong color isn't a weakness, it's the whole point, and it's why chasing lumens walks you toward the wrong light.
It compounds over a long exposure
Every second you hold a color on one spot, more light piles onto the same pixels, and once a pixel fills it can't record any more. The channel carrying the color hits that ceiling first while the other two keep climbing, and 3 channels at the top is white. That's why a saturated line goes pale in the middle and only keeps its color at the edges, and why a blue that looked weak to your eye comes back as a blown out streak.
White and RGB torches get rated differently anyway
A white flashlight's lumen number is its whole output at max on one mode. An RGB light has 3 chips in one package, and any single color is only a slice of that. Nobody publishes a per color number, so even when an RGB light carries a lumen rating, it isn't the number you'd be comparing against.
What I'd compare instead
How low it goes. For light painting the bottom of the dimming range matters far more than the top, and it's the spec nobody prints.
How it diffuses. The same light through a tube or a blade spreads over a much bigger area, so no single pixel takes all of it.
Your own test frame. Lock your settings, paint a short line in each color, then read the RGB histogram rather than the normal one. The normal one can look totally fine while a single channel is slammed against the right edge.
Happy to answer anything about LEDs, color mixing, or whatever weird thing your torch is doing :)
