4.5V LED greater than 3V?

Hi, just think that if I use 3 AAA(total 4.5V)batteries to power my 20-LED torch, so will it be greater lux(lumen) than using 2 C battery(1.5+1.5=3V) for the same 20_LED ? Can I say I provide 4.5V will be greater than 3V, even though the mAh for 2 C battery is larger?

2nd question: Always read about the luxeon power flash, 1W = ~30 lumen. ANd the single LED is ~2 lumen. But with my 20-LED torch, can I say it will become 20x2= 40 lumen ? thks.

You don't give enough information to answer your questions accurately. There are threads that explain the math needed to correcly power LEDS. You can't just throw a different set of batteries in there and expect a predictable result. Searh the forum for posts that include the string "e=i*r"

If you have LEDs that put out 2 lumens each, 20 will give you 40 lumens. Lumens appear to be additive.

Daniel

I see... My question is simple, is 3AAA battery powered 20-LED flashlight brighter & more lumen than 2 C battery 20-LED flashlight? (provided the 20-LED are the same grade)

I also confuse with two 1W luxeon flashlight, one with 3 AAA, another powered by 2 C battery, so which one should I consider, in term of brightness, last longer? thks!

Yes, I think you will be overdriving those LED's if you hit them with 4.5v. The AAA's just wont run as long as C cells would.

saratoga said:

I see... My question is simple, is 3AAA battery powered 20-LED flashlight brighter & more lumen than 2 C battery 20-LED flashlight? (provided the 20-LED are the same grade)

Click to expand...

The answer to that is no...

saratoga said:

I also confuse with two 1W luxeon flashlight, one with 3 AAA, another powered by 2 C battery, so which one should I consider, in term of brightness, last longer? thks!

Click to expand...

the 3 AAA light - will be brighter due to the higher voltage (4.5v from 3 cells, assuming you are using alkaline cells)
the 2 C cell light - will get longer run time ( the C cells have more capacity)

using 3AAAs the 20 LEDs should sag the battery voltage down to where it is slightly overdriving them (assuming alkalines, as nimh wont sag much). The 2C powered light will be rather dim and probably underdrive the light perhaps about 5-10ma and as the batteries are used up would quickly become useless for all but a nightlight.
You really need about 3.2-4 volts to drive LEDs considering some battery voltage sag due to internal resistance of alkalines. Unless you find some unusually low Vf LEDs (like the MJleds) you will be very dissapointed in the output from 2 batteries.

The reason I said that there was insufficient info no good answer? There was no info about how the light was regulated.

Is it a red led or a white one? Red takes much less voltage, around 2 volts VS over 3 for a white one. Let's assume it's white.

A 2 C light will have to be boosted. 3 volts is too low to run white LEDs without a boost. If it's boosted you'll probably break something if you try using 4.5 volts. If it's current regulated, the voltage won't make a difference as long as the voltage is correct for the inverter.

Then there's the whole question of current drain. A set of 3 AA batteries will not last long running at .6 amps. A set of 2 C cells will probably last a lot longer.

So I guess I'm saying that you have to tell us what LEDs are in use, what the existing electronics are and then we can answer the questions.

Daniel