A problem that can't be seen

I recently ordered a 501B flashlight with a 940nm P60 dropin in it from a US seller. I sort of forgot about it and a flashlight from China showed up today. I thought it was a T6 that I snagged for real cheap. I put in a battery and nada. No photons for you! Hmmm, measure tail cap current. It’s pulling a valid current. Weird.

Ah ha! I think that I know what’s going on now. US seller is in China. 940 nm is in the infrared and that drop in puts out NO visible light. The proverbial Dark Emitting Diode. A quick check with the night vision equipment and all became apparent.

Now the problem is how can one tell if a light that emits no light is on? Click-on Click-off… it all looks the same. Something tells me this thing is going to kill a few 18650’s.

most of us would not have had that piece of ‘diagnostic’ equipment

you could add a small indicator led to it, or point it out the window and all the neighbourhood bees will pay you a visit

Indicator led!
Clear tailcap with a small smd led & resistor. I’ve been planing to do it since I saw clear tailcaps are available.

What size is your tailcap?

Sort of defeats the purpose of a light that can’t be seen…

^ Tailcap! (crossed post/edit)
Pick a resistor that gets it extremely dim?

You could also tell by the give when you press the tailcap. Clickies click in & click out, your tailcap is more ‘mushy’ when its clicked it.

How about a liquid crystal sheet that changes color after absorbing the IR radiation as heat ?

Rare earth IR detection cards are also available.

[edit] sold here : http://www.i-fiberoptics.com/tool-detail.php?id=560

Or you can just use the camera in your phone and see the if the led is on, IR appears bright to the camera. I use it to check if the TV/DVR remote is working.

doesn’t its head get warm if left on?

if its high powered can’t you just point it at your hand and feel the warmth?

have you got a p60 host with tailcap lock out?

Or use your night vision equipment? :slight_smile:

Perfect excuse to go get some NVG's and use it as an illumination source

wow… Night Vision Gear…
with that gear. would Moonlight mode be sufficient to “light” up the whole room?

I have it on very good authority from the good Doctor (?) that a sonic screwdriver will give very accurate readings from this sort of drop-in.

Same as helios. For standard reverse clicky, there’s an obvious play when half clicking when switched on (that soft click for changing modes). During off, this play is not apparent.

Once you familiarize the difference it’ll be walk in the park to know the on/off state.

yes, this works!

I also use this with any remote (tv, radio etc) that isnt working well, or not at all.
Just point your phone camera on the Led, and push any buttons on the remote. this will show up on your phone!
if it doesnt, then the remote is broken.

Convert it to a twisty tailcap, get rid of the switch. I did that for the old 501b mounted on my varmint gun. Even when it's OFF and backed out about 1/2 turn, the spring is strong enough to keep the contact broken, but there's enough slack in the crappy threads that just a little thumb pressure turns it on. Screw down tight and it's on. Unscrew more than 1 turn and it's locked out. In between it's momentary.

I replaced the all the switch parts with a similar thickness stack of metal, then reinstalled the switch retainer. Works nice.

940 nm is far enough into the IR that most cameras will not pick it up. Even 3rd gen night vision goggles are not very sensitive to it.

Look at the light through a cheap camera (The one in a mobil phone can be used), they are usual IR sensitive.

Easily! Even a AA mini-mag with an incandescent bulb/visible light filter looks like a spotlight at 200 yards. It is one place where an incandescent outshines an LED.

Could you make a little IR “receiver” with a little visible LED, something that you could attach to a lanyard to the light?