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I spent the last month obsessed with finding colors that can't be displayed on a conventional screen. This is what I found. moultano.wordpress.com/2026/06/19/w...

fun fact that's not covered: with a bright enough 720nm LED in the dark, you can see beyond CIE 1931. i use a custom-made ~40w Emisar flashlight. it lies outside the rod cells' spectral response curve and only stimulates the cones, which is ordinarily impossible for light

because it only stimulates the cones and not the rods, it has numerous characteristics that are perceptually fucked and evil. it's the reddest red anyone has ever seen. it turns purple at the edges, stops after 10 feet, looks dim but feels bright, and is weirdly high resolution for a dim light

because the rods should ordinarily always be stimulated when the cones are going off, the brain can tell something is viscerally wrong with the light, but the visual sensation (?) of it is impossible to describe accurately

it doesn't affect night vision *at all*, even compared to ordinary red LEDs. it's blindingly bright when swept across the eyes but leaves no afterimages. you can find your way around with it at night and look up and the milky way is just There.

I showed it to an older fella who'd had artificial lenses implanted and he went "WHOA" and covered his eyes and said it was the most insanely bright red light he'd ever seen

cone cell response to dim light is nonlinear, so combined with inverse-square, it perceptually falls off way WAY faster than light should past a certain point a friend called it my "diabolical flashlight"

to get ahold of one, you have to order a light with 660nm photo red emitters from intl-outdoor.com, then email hank with your order number and tell him you want 720nm far red instead. mine's a D4V2 because it was cheap but any that have the 660nm option should work.

Is there some reason it's not an official option? Is everyone reading this thread going to buy him out and some of us end up with mere 660nm lights?

congrats on inspiring an entirely unneccesary but deeply curious purchase

What kind of back light switch to get? Or does it matter?

it occurs to me: because it's so monochromatic, it also allows the eye to bring it into perfect focus unaffected by the chromatic abberations that affect the eye as an imperfectly corrected system. it's actually *sharper* than white light because it can be focused to a single point

I will note in case it's not obvious to anyone reading this: if you purchase this flashlight, do NOT shine it in anyone's eyes directly, and especially not at close range; I've never checked to see if it makes my pupils constrict for retinal safety. It does trigger a blink/aversion reflex, though.

When you say “cheap” here what are we talking? Cuz this does sound cool as hell

$36 for the cheapest version of the d4v2, a bit more if you want the Lume X1 driver that makes it way more efficient but a bit less bright at maximum power