Blue cree @ 3V

[Fallingwater]

My girlfriend has a crappy old incandescent 2xAA pocket light she's affectionately attached to, despite its absolute lack of any performance to speak of.

I asked if she'd let me mod it and she said yes.

I want to do something extremely simple, with no regulators, chips and whatnot.

White Crees need about 3.7V, so they are right out.

But blue Crees are specced as "3.2V - 3.4V", so I'm wondering what kind of output I'd get with a blue Cree direct-driven by two alkaline AAs.

My idea is it'll come nowhere near full power, which is good because the light is completely plastic and it'd be extremely hard to properly heatsink the emitter. I figure it'd give much more light than the original VERY dim incandescent bulb while still drawing little current and so not overtaxing the AAs.

What do you think? Any ideas about current consumption and performance of a blue Cree at three volts?

Thanks

 

[Marduke]

Well, I'll give you a bit of encouragement. I have played around with a white Cree Q5, and it would run decently off a single CR123 direct drive. Blue should work just fine direct drive as mentioned, and would make for a nice light.

 

[DM51]

Moving this to 'Homemade & Modified'.

 

[VidPro]

idea use lithium AAs like the energyser L91 things, 2 of them will pump out 3.4V - 3.0 and down and drive White and blue leds direct, not high but usable, much more usable than alkalines.

(of course you would have to check the actual current, but its cheap fast and as it dims it lasts a long time, also the led quits triggerring when the cells are exhausted, ~2.4v so there should be no reverse charge.)

Blue aint diddly voltage different than the white, cause white uses a blue original anyways, so i wouldnt expect much more from the blue than a white as far as current draws, they are pretty relative, with the blu looking neeto and the white putting out more actual light even with any voltage difference.

Also there are QUAD and 5 DIE white and blues in 5mm 8mm and 10mm that will do about 80ma and overdrive at about 150ma , fit in small stuff, but would not have the longevity of a high powered led. so if it was "socketed" and there was a spare to replace in 300 hours, that is a cheap quick way to mod a pocket light.

 

[Marduke]

Could also resistor down a Red Cree

They only need 1.9-2.2v

I'd be tempted to just direct drive it, knowing that the life of the LED would be much shorter, but unlikely that you'd ever use it that much

 

[f22shift]

Could also resistor down a Red Cree

They only need 1.9-2.2v

I'd be tempted to just direct drive it, knowing that the life of the LED would be much shorter, but unlikely that you'd ever use it that much

what resistor would you need

 

[Marduke]

what resistor would you need

Depends on your desired current, and the voltage source. There are online calculators for it.

 

[Fallingwater]

Green Crees are specced at the same voltage as red ones (at least by DealExtreme), so I'd use a green one instead.

The question that arises is: what current can a green LED withstand without cooling, or maybe with just a small piece of metal on its back?

 

[2xTrinity]

I would not recommend blue at all, as a single-color it is not very useful, the other colors at least have some redeeming characteristics. I would recommend green instead -- it will provide better contrast and visibility than either blue or red.

 

[VidPro]

the voltage on greens is (a little) lower than the blues (usually) even when the spec sheet shows the same, they would be the closest direct match to 2x1.5v