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Strongest 3V LED with pins? Answered

I'd like to build a LED into an empty light bulb that can run on 3V (from button cells). So I can't use the normal screw-in leds that are sold because they are all 12V at least. I'm planning to build the LED into the lightbulb myself, and connect it manually to the batteries.

I'd like my LED to be as omnidirectional as possible. So what LED would I be able to use for this, and would I need some sort of diffuser or something to make the light shine in all directions? Would I be able to get up to about similar lumens as a 40W incandescent bulb?


Thanks for the tips guys. I'll see what works best once I get this project under way. Some other things have gotten in the way of my little hobby project, so it's on hold for a while.

Hmm ok that makes sense. It's not for a magic trick, but basically I need the bulb burning without it being plugged in. I guess it doesn't have to be 40W, as long as it looks like the lightbulb is on, and generating some light. I've found some LEDs that say they generate 50,000 MCD, but I think that's at 100mAh, which is considerable.

The problem is the space I have for batteries. I only have a cylinder of about 4cm long and 1.5cm diameter to work with to store my power source...

Don't fall for the trick of MCD. That is not brightness. That is intensity. You can have a 50,000 MCD led w/ 10 degree apex angle is only 1.1 lumens. 5000MCD @ 170 degree angle is about 27 lumens. Lumens is actual light output, and mcd is basicly the intensity of the light when it hits an object. A laser would have a REALLY high MCD in some cases because of how well focused the light is.

If you want good light quality and usable amount of light, stay far away from the really tempting eBay deals. Those LEDs almost never meet the specs advertized, and even if they do, they generally fade and degrade over time and fail really quickly.

Lithium batteries will be most suitable for your application. a 14500 cell may be perfect. (14 mm wide, 50 mm tall, and O, or round. Thats a breakdown of that number.) or a CR123A battery. They may not last long driving a large LED though.

Use Lion batt .... they are Twice the power, Half the weight and Ten times the cost


3 years ago

Going with power LEDs like the cree XML will probably be best. They are designed to be very efficient, and I think the cree XML2 is 120lm/w at a few watts.

You will not need to worry about any current limiting resistor, and probably will not need a heatsink either, as the internal resistance of the button cells is more than adequate. That will probably deliver 50-100 lumens or so, which is a respectable amount of light. I know the cree XML is way overkill, at 1040 lumens @ 10W for this application, but thats the point. Big LEDs driven less hard will have higher efficiency, and in this case, that really matters.

To get 40W of equivalent incandescent light, thats 500LM. You will need to drive the XML with 5W of power, and add as big a heatsink as you can get away with in a small light bulb housing. It will produce about >4W of heat, so you can do some thermal calculations to determine the heatsink required. I can tell you, thats not easy. Trying to fit a big heatsink and (in the case of standard LED lamps, a inverter) is NOT easy to do. Thats why LED lamps on the market are still very expensive, require almost cutting-edge technology, and just recently really hit the market.


3 years ago

Just assume your 3V LED is 100% efficient ( it is Not ) but at the peak current of 30ma the power would be P = 3 x o.03 = 0.09 watts .... That is over 400 times less then a 40 watt light bulb..


You can get LEDs that will give that much light and more that run off 3V but they will drain a button cell battery in a matter of minutes. Just look at all the tactic flash lights out there rated at 100 lumins or more and run off a single AA or AAA battery. The trick is to defuse the light so you get a wider viewing angle. So the easiest thing for you to do is adapt one of those flash lights into the bulb, With the light shining at a cone shaped reflector at the top of the bulb. But why a battery powered bulb? This for a magic trick?

Oh and no single LED with pins will give you the amount of light your looking for. Those bright LEDs are all surface mount and most require a heat sync of some sort as they can get quite hot. They require some sort of driver circuit to take the voltage and boost the current output output. Ultimately those 12V LEDs maybe only use 3V but they use a lot of current. So the driver take a low current 12V input and converts it to a lower voltage, higher current output for the LED.