Brightness vs. Battery Drain?

[scott]

I know ZERO about electronics--and I'd like to keep it that way. I like flashlights. I do not like technical details and terminology. Just flashlights. Mostly LED flashlights.

I think about the "brightness" vs. "battery drain" issue like this:

If two different led lights are fed by the same power source, (such as each using 2AA batteries) and the first flashlight is twice as bright as the second, then the second flashlight will burn for ABOUT twice as long as the first.

I realize there are certain differences in effeciency, but those differences are slight-- right? I really don't know. I said this is how I "think about the...issue." So-- am I thinking about this correctly? Is it ABOUT right?

I am asking because, generally, I'd like to know. More specifically, though...

In the reviews forum, the run-time plot for the new Terralux Ministar 2 has been posted. On 2AA batteries, the light took about 5 hours to reach 50% brightness. If my Opalec Newbeam runs for about 10 hours on 2AA batteries, is it safe to assume that the Ministar 2 is ABOUT twice as bright as the Opalec? (Assuming variables, ABOUT=15-20%

Scott

 

[popsgee]

Probably safer to say the Terralux draws twice the current. Unless one of them has a regulator.

 

[Rothrandir]

there are so many variables here, that i'm not even going to attempt to answer... /ubbthreads/images/graemlins/icon15.gif

some things to keep in mind:
not all curcuitry is the same (effiency wise)
not all leds are the same (efficiency wise)
leds tend to be more efficient at lower levels
optical effeciency plays a part (reflector, lens, etc)

if you have 2 lux3 lights (lets say they're badboy's in a minimag), and one of them is a bb500, and the other is a bb1000)
the bb1000 will not be twice as bright, and will run less than half as long.

 

[StuU]

Leds in commercial lights are frequently overdriven ie the Inova X5 has leds driven at 50ma each. Above a certain point, the led produces a lot more heat than light.

A flashlight that draws 100ma with one 5mm white led would a lot less bright than a light that draws 100ma with 4 leds.

Stu

-------------------

Ubi dubium ibi libertas:

Where there is doubt, there is freedom

-Latin proverb

 

[Lagged2Death]

Batteries - alkalines in particular - don't react absolutely linearly to differing levels of power drain, either. A circuit that draws 1000mA from a cell will deplete the cell more than twice as fast as one that draws 500mA. At higher draws, the battery's internal resistance becomes a significant part of the circuit's total impedance, and can waste a significant amount of the battery's power.

 

[jayflash]

Scott, SOMETIMES, the twice-as-bright-light will have 1/2 the runtime of another, 1/2 as bright light. If OVERALL efficiencies are equal than the ratio will be valid regarding brightness vs. runtime.

 

[gadget_lover]

The only time you can make the "twice-as-bright-light will have 1/2 the runtime" assumption is when both lights have the same type of LED and both use the same power supply and power handling.

Case in point;

A light with an 'M' binned 1 watt LED will use exactly the same power as a 'Q' binned LED, but the Q binned LED will be as much as 3 times brighter.


Daniel

 

[kj]

I agree with Rothrandir and I also cannot answer the original question, but this runtime chart may help you to understand the issue a little.

Except DB700/PM6, they all use the same binned LED, same design circuit, same brand batteries, same reflector and same housing. Even with these conditions, the "twice-as-bright-light will have 1/2 the runtime" theory does not hold good.