Converting blue LEDs to white

[bobski]

Hey folks... I bought a Rayovac 1AA Sportsman Xtreme Headlight last night and have been reading through the associated threads. Everyone seems to agree that it's blue LED is pretty much useless as far as it's intended purpose (tracking blood trails) is concerned, but it can't be replaced without destroying the light's casing. Getting toward the end of one of the threads, I came across a comment which got me thinking:

Its a shame theres no opening this baby I'd love to glow epoxy the PCB around the emitter, and get rid of the blue led

Why not glow-paint the blue LED? Blue charges GITD stuff nicely, maybe a thin coat could keep up a constant, bright glow when the LED is on. Then I remembered that blue and appropriately filtered white LEDs make things fluoresce, including the phosphors used in white LEDs:

Though my digi-cam doesn't do it justice.

So has anyone ever tried converting a blue LED to white? Is there a suitable paint available somewhere that has similar fluorescent characteristics to white LED phosphors? I guess I could grind off the lens of the blue LED and glue the lens of an omnidirectional white one in it's place, but I would prefer a more direct approach.

 

[bobski]

Well, since the discussion was just roaring along here, I decided to try the white LED cap method.

Turns out there's a reason blue LEDs make the white phosphors fluoresce - There's a blue LED at the core of them. I'm sure I could have looked that up somewhere.

Compared to the headlamp's blue LED:

The white LED looks kinda purple in that pic, but it just looks a deeper blue IRL.

I ground the lens of the blue LED down flat with a dremel... This pic is mid-way. I had to go down another millimeter or two so the white cap would clear headlamp's diffuser.

The ground LED lit:

Cap - meet LED, LED - cap.

Epoxied:

Guess I got some air bubbles around the edges...

I'll do beam shots in a few hours once the epoxy has cured.

 

[bobski]

Well, the converted LED is a success IMO, but functionally it's pretty weak. I guess that's to be expected from a ~.06 watt LED with it's light thrown in all directions. It's just enough light for reading or to avoid stumbling into things in the dark. Output wise, I would equate it to a 2AA classic mini-mag in candle mode, but perfectly even.

Dual red mode:

Converted white omni:

1 watt Luxeon with diffuser in place: