Relationship between LED bulb, battery, and brightness

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I've done some looking around on Google and on this forum to find a satisfactory answer to a question about flashlight brightness, but everything I found seemed to brush over the details I was looking for.

Let me illustrate my situation: I have an RovyVon Aurora A3 flashlight that can light up an entire room even though it's less than three inches long and weighs a third of an ounce. It also appears to contain only one LED.

So now my question: what exactly makes one flashlight brighter than another? Could you hook up a cheapo keychain flashlight to the same battery as my tiny flashlight to get the same brightness? Does it depend on the LED used? Or how the thing is wired?

In the case of my Aurora A3, why doesn't the LED burn out immediately? I don't know if these are dumb questions, but it suddenly strikes me as very weird that my A3 can contest a brick-sized Maglite in terms of brightness.

(BTW, I know most flashlights don't crank out as much brightness as possible to reduce cost and improve runtime, but I'm talking about pushing hardware to it's limits)

 

[Chicken Drumstick]

There are quite a few things at play.

Different LED types and sizes will vary how much light they can make. Generally speaking, physically larger LEDs have potential to make more lumens.

To make more lumens is all about current (amps). The more amps you feed an LED the brighter it will become (assuming the voltage is also correct). But also the more heat. There will be a certain point where this will drop off or the LED will burn out.

A 'driver' (small circuit board) will control the amps to the LED. So different drivers can produce more output. But there is a limitation. In order for the driver to give the LED more amps, you will need a battery source (power source) capable of supplying the demand.

Then there is also the optics end of the torch. i.e. a reflector or lens. There is a relationship here. A focused beam of light will project light a long distance, but may not light up a room very well. While a flood of light with a very wide beam will light up a big area, but not light up anything very far away. So the human perception of brightness can be influenced.



To give some examples.



LED:


Something like the Cree XP-E2 is very small. While the Cree XM-L2 is many times the size. The XM-L2 will make more lumens for a given amp draw compared to the XP-E.

example of some LED sizes:

This is a general trend however and there are exceptions. It is also worth noting, smaller LEDs often have a higher surface brightness. And because they are smaller, the optics can focus the beam better. So a smaller LED will usually provide a more throwy focused beam. While bigger LEDs will offer more lumens, but a more floody beam in the same size optics. (bigger optics nearly always produce more throw than smaller ones).


I find thinking of lumens in a similar way to torque for engines works. i.e. while more is always desirable. What you do with it can often have more dramatic results. Which is why a 2.0 litre diesel turbo can make more torque than a Ferrari V8. But the Ferrari V8 will still make a lot more Horse Power.



Drivers:

Drivers control all the modes on a light. Such as the High and Low outputs and any blinky modes like strobes. Many drivers are conservative and they don't push the LED all that hard. Many typical drivers might only run something like an XM-L2 LED at 1.5-1.9amps in High mode. However the modding community has proven that such an LED will easily handle 3-5amps, but with a lot more heat generation.

So there are many lights these days that support these higher currents, or driver boards you can buy and retro fit to some lights. That allow much more current. Ultimately allowing the lights to be much brighter.



Batteries:


When it comes to powering an LED. You need a stable voltage that matches the forward voltage (vf) of the LED. Should this voltage drop, then performance will also drop. As amps are drawn from a battery, the voltage will sag. So a battery that sags less and allows high current draws will, assuming the driver & LED combo. Allow much higher outputs.

There are different chemistry batteries. Li-ion is generally the best performer, followed by NiMh. As a rule, a physically bigger battery will perform better than a small one. So a flashlight using an 18650 vs one with a 14500 (AA sized) Li-ion battery, will have a lot more potential.

 

[lightfooted]

Chicken pretty much answered most of your questions with their reply so I'm just going to say welcome to the 21st Century where we no longer have to make fire to get light. Okay so it's not exactly fire...but a hot wire in a glass bulb with some gas to keep it from burning away the metal instantly is basically incandescent tech. Sure an LED can get hot enough to start a fire nowadays, but they aren't designed to and it usually means driving them pretty hard to do so. They are better at creating more light with less heat as a result. Incandescent lights are literally creating heat with a side benefit of creating light.

 

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Wow, thanks for the in-depth reply! This was exactly the info I was looking for. (Well, actually, I wasn't really sure what info I was looking for, but now I know it was this).

I find thinking of lumens in a similar way to torque for engines works. i.e. while more is always desirable. What you do with it can often have more dramatic results. Which is why a 2.0 litre diesel turbo can make more torque than a Ferrari V8. But the Ferrari V8 will still make a lot more Horse Power.

So when a flashlight has a really high lumen count, that doesn't necessarily mean it's going to be better than, say, a Maglite with an adjustable beam. In that case, a flashlight's "brightness" would be more about manipulating the light than about trying to pump out as much light as possible. Interesting.

Drivers control all the modes on a light. Such as the High and Low outputs and any blinky modes like strobes. Many drivers are conservative and they don't push the LED all that hard. Many typical drivers might only run something like an XM-L2 LED at 1.5-1.9amps in High mode. However the modding community has proven that such an LED will easily handle 3-5amps, but with a lot more heat generation.

So in the case of my A3, it probably just has a driver that allows as much current as possible to make the LED as bright as it is. As you could easily guess, though, it gets really hot after a few minutes to where you can no longer handle it. I'm guessing that's what some flashlight manufacturers are trying to avoid when they limit the current flow.

When it comes to powering an LED. You need a stable voltage that matches the forward voltage (vf) of the LED. Should this voltage drop, then performance will also drop. As amps are drawn from a battery, the voltage will sag. So a battery that sags less and allows high current draws will, assuming the driver & LED combo. Allow much higher outputs.

If I understand correctly, the forward voltage is the minimum voltage required to get the LED to turn on and you want that voltage to stay constant as the current is changed (I'm assuming for stability reasons). But it sounds like as long as you have a good battery, you don't need to worry about it.