There’s a recent post on r/flashlight about ‘far red’ light. It includes a (desaturated) video made with a camera without an IR filter. The poster is using a “3 watt 730nm LED from eBay.”
I enjoy looking at objects lit by UV (with protection! 8^) ) but hadn’t heard of playing with light at the other extreme of the visible spectrum!
Searching for 730nm emitters revealed Cree’s XP-E ‘Far Red’ variant. It seems there’s no XP-E2 replacement yet.
In the video he was able to see black text written in sharpie on black cloth because the cloth showed as white while the sharpie was still black. You could send secret messages? Idk.
Right? On the /flashlight post I said I have the 670nm H502pr Zebralight headlamp unfortunately it’s not “far red” enough for the effect to work so I said if Zebralight is listening I would totally buy an H602fr/H502fr with the far red emitter so I can get my spy on.
Did you buy them from that link? Just curious.
I have some red osram oslons but I got them from some LED tail lights I disassembled so I have no idea on their specific wavelength / bin
Incandescent light bulbs have a lot of far red and IR. So unless this is mostly invisible so that the pupil doesn’t contract or the intensity is very high, I don’t think it’s a problem. I would think 720-750nm is very visible still. So probably no need to wear any glasses unless you’re viewing it directly or in a pitch black room.
At least the ‘green’ cone in the human eye has no sensitivity for light longer than 650-700nm, so anything higher than 700nm will just be recorded by the red cone and will appear the same dark red colour. Also from 700nm on your eyes become highly insensitive so you need enormous power to get a decent visible illumination. I think anything higher than 720nm will appear pretty invisible.
I assume those XP-E Photo Red are more useful than Far Red, right? There are a lot of controverse discussions whether or not deep red light (> 650nm) is better for maintaining one’s night vision ability compared to normal red light with 625-650nm (= XP-E2 red).
As long as the intensity is high enough you will see it (there is some sensitivity up to 800nm, probably a bit different for each individual) , it is a very inefficient way of illumination though, you need hundreds of times more radiation power to see the same intensity as green light.
I’ve built lights using XP-E 660nm “photo red” emitters, and XQ-E 670nm emitters. Both are more pleasing to my eye than normal 630nm red. In fact I don’t care for the 630s much at all since trying the higher wavelength stuff. They do indeed look quite orange in comparison. Whether they’re actually more useful or not, I can’t say. But I do like them quite a bit better.
I’ll have to order up some “far red” stuff to play with.
I saw you in the reddit post and was hoping you’d chime in here. :THUMBS-UP:
I’d like to try a far red triple. I have a spare copper spacer, some Carclos, and an empty S2+. It’s even red.
I thought I’d either reflow some bare emitters onto a Noctigon triple, or use this triple from LEDsupply rewired for parallel:
The loaded board from LEDsupply is $12 with free shipping. Three bare emitters from Digi-Key would be about $9 with shipping.
I don’t have any experience with limiting a driver’s output. Maybe I could tweak Bistro’s code to limit the power of an MTN FET + 7135 driver? I already have a couple and would rather not fiddle with ordering components to build or modify a driver.
You want different hardware, not soffware. A 7135 current controlled driver would work for these (such as a 3A biscotti driver from Simon, so for 1A per led). And hope for the best because a lot of overvoltage needs burning off by the driver A lower voltage battery like a LiFePo battery could help with that.
I assume that would be better even, you need more than half a Volt overhead and this is almost 2V so it should be fine , but you want a 3A or more 17mm buckdriver, with half-decent firmware, does that exist?
