Which LED for superbright Torch?

[jamoor]

At work I have been given the assignment to develop what is essentially an LED torch, thing is this thing can run to the cost of £30-40.

The "torch" can work off 2x AA batteries and needs to be blindingly bright! It can only be 1 LED though and the LED can't be too big either.

Having a quick read around on here, the word "Cree" comes up often, is it best to persue these LEDs?

 

[ev13wt]

At work I have been given the assignment to develop what is essentially an LED torch, thing is this thing can run to the cost of £30-40.

The "torch" can work off 2x AA batteries and needs to be blindingly bright! It can only be 1 LED though and the LED can't be too big either.

Having a quick read around on here, the word "Cree" comes up often, is it best to persue these LEDs?

This wheel has been invented. Cree is IIRC the current technology leader in the LED industry,
Keep reading. What is your wanted form factor? Batteries next to each other or behind each other. Also 2x aa and "blindingly bright" are condratictory.

-Develope means what? Buying from china and relabeling or are you doing the entire thing yourself?

 

[carrot]

If small is a concern consider the Cree XP-E. It is an XR-E in a smaller package. If you can go a little larger and push the batteries hard you may be able to power an MC-E (4-die XR-E, basically) at a respectable drive level.

 

[jamoor]

This wheel has been invented. Cree is IIRC the current technology leader in the LED industry,
Keep reading. What is your wanted form factor? Batteries next to each other or behind each other. Also 2x aa and "blindingly bright" are condratictory.

-Develope means what? Buying from china and relabeling or are you doing the entire thing yourself?

Hi,
it's not actually anything to do with torches, it's in a different market entirely and it's a component of a larger product.

2 Batteries in series ideally.

Is there any way for the LED to simly turn off once it gets down to a specific voltage or something? Traditionally as batteries wear out, they get dimmer, can you simply turn off the led if there isn't enough power going to the LED?

 

[Jarl]

You'll need to use a boost driver. What this does is takes the voltage of the batteries, and increases it to the voltage needed for the LED to run. As the voltage from the batteries drops further, more current is drawn, to keep the power going to the LED pretty constant, until the batteries are nearly totally dead, at which point it'll normally drop to a nice low level of light which you can use to find another set of batteries.

 

[jamoor]

How effective are these "boost drivers"

Any idea how long it will spend dim, or how dim it would get? Or does that vary greatly?

If it's 2 steps or 3 steps then it sounds ideal
e.g. full brightness for 3 hours
25% brightness for 20 mins.

 

[Jarl]

You can vary the length of full power- it'll drop out of full power when the batteries run out of juice (though some boost drivers may just stop working at this point, most give a moon mode), so the higher the draw, the brighter the light, but the shorter the runtime off 2xAA's. If this is part of a bigger assembly, could you use an alternative power source?. Generally, moon mode is 2 to 5% of original output, and lasts for several hours.

 

[Gunner12]

Maybe looking at something like the Fenix E20 or even the Romisen RC-N3(IIRC the RC-N3 has around 3 hours runtime before it drops out of regulation) and modeling something similar?

Boost drivers for 2AA seem to be 70-90% efficient. The dimming will depend on the driver and batteries. Look at some of the runtime graphs to get an idea of what happens when they drop out of regulation. Most drivers aren't complicated enough to lower brightness in steps.

Cree is a company that makes LEDs. Their XR-E, XP-E, MC-E and maybe a few more models are some of the current generation of LEDs. Seoul P4 and P7 are also part of the current generation, so is the Luxeon Rebel and TFFC K2s.

:welcome:

 

[jamoor]

Interesting, thanks alot everyone!

Are Cree LEDs expensive? Any idea on their prices?

Also, does anyone know any companies in China that can custom make an LED based torch type thing, or even other LED based products?

Also, you mention that you should get 3-4h from 2AA, is there any way to lengthen that, or will that sacrifice the brightness of the light?

I don't really need brightness lowering in steps, essentially I need an everything or nothing scenario.

The light needs to be at 100% brightness, or off.

 

[Derek Dean]

Howdy jamoor and welcome to CPF,
Be sure and check out the CPF Welcome Mat, you will find answers to many of your questions there:
http://candlepowerforums.com/vb/showthread.php?t=172991

You might also want to visit the 'Homemade and Modified Lights" forum. I think it's exactly what you are looking for:
http://candlepowerforums.com/vb/forumdisplay.php?f=17

Good luck with the project.

 

[Gunner12]

The Cree XR-Es are $5-10(maybe up to $15 for the R2 bin) from what I see. Cheaper if you buy in bulk.

I suggest you check out the Romisen RC-N3, pretty similar to what you are looking for for around $20 USD.

You cna lengthen the runtime by lowering the current to the LED, that will also decrease the output though.

 

[LEDninja]

Also, does anyone know any companies in China that can custom make an LED based torch type thing, or even other LED based products?

Be aware some Chinese companies will do a product overrun and then sell the extra product at a much lower price than the designer's company.

A Swiss company used to sell a solar powered keychain torch for $35. DX is now selling the same thing for $3.50.

LRI invented the photon keychain light at ~$5. Faux-tons are going for 10 for $5.

Elektrolumens gave up subcontracting his designs to be manufactured in China. He kept getting complaints his torches are too expensive - Exactly the same thing is available elsewhere at half the price.

If what you are putting together is a subassembly which is useless by itself go ahead. Check out alibaba.com where the Chinese manufacturers and exporters hang out. But if the item is a finished product I would hesitate to subcontract.

As you are at the prototype stage it would be unwise to subcontract to any place you can not visit easily to sort out technical problems.

One other concern is the Chinese seem to build their torches to fit the nominal small battery. As current NiMH are a little bigger than the basic 'heavy duty' battery, they may not fit. I also ran into a problem where protected 18650 batteries would not fit a 18650 torch. Only the less safe unprotected 18650 would fit.

 

[jamoor]

Be aware some Chinese companies will do a product overrun and then sell the extra product at a much lower price than the designer's company.

A Swiss company used to sell a solar powered keychain torch for $35. DX is now selling the same thing for $3.50.

LRI invented the photon keychain light at ~$5. Faux-tons are going for 10 for $5.

Elektrolumens gave up subcontracting his designs to be manufactured in China. He kept getting complaints his torches are too expensive - Exactly the same thing is available elsewhere at half the price.

If what you are putting together is a subassembly which is useless by itself go ahead. Check out alibaba.com where the Chinese manufacturers and exporters hang out. But if the item is a finished product I would hesitate to subcontract.

As you are at the prototype stage it would be unwise to subcontract to any place you can not visit easily to sort out technical problems.

One other concern is the Chinese seem to build their torches to fit the nominal small battery. As current NiMH are a little bigger than the basic 'heavy duty' battery, they may not fit. I also ran into a problem where protected 18650 batteries would not fit a 18650 torch. Only the less safe unprotected 18650 would fit.

It's just a compeltely useless component on it's own, no real help to anybody, so that's not a worry.

What's a nonminal small battery? AA?

 

[Jarl]

AA's can vary in size.... Big ones and small ones. What LEDninja was getting at was that you might end up with a light designed to run off the smaller AA cells, so when you put in your larger AA's, they won't fit.

If this is part of a larger assembly, why the use of 2xAA?

 

[carrot]

Fauxtons and Photons, FYI, are totally separate categories. The Photons are made in the USA, and have far superior construction to the Fauxtons. It is not an overrun, it is a poorly designed clone.

 

[carrot]

AA's can vary in size.... Big ones and small ones. What LEDninja was getting at was that you might end up with a light designed to run off the smaller AA cells, so when you put in your larger AA's, they won't fit.

If this is part of a larger assembly, why the use of 2xAA?

And by this, we are thinking the different chemistries of AA, such as carbon-zinc, alkaline, lithium, NiMH, and the rarer lithium-ion, which may come in slightly different sizes depending on manufacturer, chemistry, etc.

 

[uk_caver]

Jamoor,
Assuming you're UK-based (from your use of the £ symbol), if you wanted something to start playing around with, and get some idea of brightness, the 2*AA LED torch available at Tesco (generally £10, though when I got one a couple of months ago, it was only £8) has a Cree LED and a driver in.

The driver in the torch I bought to look at with seems to be about 75% efficient, and gives ~520mA output running off a pair of AA rechargeables, so it's running the LED at about half maximum power. The optic is a push-fit, so could be easily removed if you wanted to see the effects of a flood beam, rather than a spotlight.