is it true multi emiter flashlights are more efencent then single?

[raggie33]

just wondering my ocd is asking

 

[idleprocess]

In general, LEDs are more efficient (greater lumens per watt) at lower drive currents than at high drive current. Thus for almost any level of output - with like LEDs, similar driver/optical losses, similar thermal management - a multi-emitter light will generally be more efficient than a single-emitter light at the same lumen output since the single-emitter light is obligated to drive its LED markedly harder.

 

[raggie33]

cool ty

 

[jon_slider]

> more efencent then single?

no because multi emitter floods a wider area, so if both lights are at 1000 lumens, the single emitter will put more lux on a smaller target and will look brighter.

to make up for it, the multi light needs to increase its power level, which means it is going to use batteries faster, and that is Less Efficient

the Lux (how bright the target is illuminated), is much lower on the multi light, IF both are set to the same lumens.

 

[idleprocess]

> more efencent then single?

no because multi emitter floods a wider area, so if both lights are at 1000 lumens, the single emitter will put more lux on a smaller target

to make up for it, the multi light needs to increase its power level, which means it is going to use batteries faster, and that is Less Efficient

the Lux (how bright the target is illuminated), is much lower on the multi light, IF both are set to the same lumens.

The simple definition of efficiency is the fraction of input energy that is converted to useful output - lumens per watt because the wide spectrum of visible light and our eyes' variable response across that spectrum makes 'radiated watts' a meaningless measure.

You're describing an altogether different performance metric that's a function of optics and packaging constraints: given the same volume of space one can collimate a single emitter far better than multiple emitters at the expense of covering a far smaller area. I can't locate the dogs' leavings effectively with my D1, nor do I put much light where I want it on a woodline 100 meters away with a D4.

And that 1000 lumens from a single emitter takes more watts than from 2+ emitters.

 

[Derek Dean]

Hmmmm........

 

[Lynx_Arc]

One other thing is if the emitters aren't the same you could have a higher efficiency single emitter put out more light than several lower efficiency emitters using the same amount of power and also drivers differ such that some are designed better for efficiency at some levels than others. A Zebralight with a single emitter may be more efficient that a cheap knock off chinese light with multi emitters.

 

[LEDphile]

> more efencent then single? no because multi emitter floods a wider area, so if both lights are at 1000 lumens, the single emitter will put more lux on a smaller target and will look brighter. to make up for it, the multi light needs to increase its power level, which means it is going to use batteries faster, and that is Less Efficient the Lux (how bright the target is illuminated), is much lower on the multi light, IF both are set to the same lumens.

No. While some multi-emitter devices may have a wider beam than single-emitter devices, there is no technical reason why you can't have the same beam/field/spill angles in the far field with a multi-emitter source that you can with a single-emitter source (and in fact, this is reasonably common in non-flashlight applications). Now, there are certainly some tradeoffs that come up if you have a constrained optical system diameter, but that's a specific situation and not the general case.

 

[idleprocess]

One other thing is if the emitters aren't the same

My D1 (single XP-L HI) is more efficient than my Maglite triple (3x Luxeon III) by a factor of ~4, but this sort of distinctly unlike comparison breaks the cetaris paribus principle.

 

[jon_slider]

you can see on the packaging that the light with one LED and less lumens than the triple, has more throw

the triple has more lumens, but less throw

the difference is due to beam focus
the single LED has a smaller hotspot that is brighter than the wider hotspot of the triple

the difference is due to the size of the hotspot:

So, in terms of throw, a single is more efficient than a triple.

 

[idleprocess]

So, in terms of throw, a single is more efficient than a triple.

No real argument there, however throw is but one of many metrics to consider in a flashlight - and not necessarily the most important one for any given user.

Trying to locate dog leavings with a thrower is like looking at Google Earth through a straw; trying to defeat inverse-square with brute-force flood snaps the pupils shut with foreground light thus something 100 meters away is more difficult to see than that same cd/lux at 100m away would be in isolation.

A modest improvement in efficiency may not be the prime consideration for a given user either, however that's the question that was asked.

 

[orbital]

+

As it's been said, emitters driven medium or less will be most efficient.
How you focus that emitters output or not, can give more lumens or more lux.

So, is a triple for throw less efficient than a triple for flood?
no, it'll just appear to have less lumens.

The output 'pie' doesn't change.

 

[jon_slider]

both are true:
1. I agree that the LEDs in a triple are operating at a more efficient power level, than a single LED

2. Im also saying that a triple will use batteries faster, because it works harder, to cover a wider area


maybe an example will help
pretend I have 4 identical lights, each capable of two modes, either 333.3 lumens, or 1000 lumens...

1. pretend I use three lights, each with one LED, set to 333.3 lumens, and I tape them together into a triple bundle.

each of the triple lights is producing 333.3 lumens, so three of them add up to 1000 lumens. But the Throw and Lux dont go up by 3x, because the beams are not focused together.

2. I use the other light with one LED, set to 1000 lumens, with a typical reflector with hotspot and spill.

the three light bundle will obviously be dimmer than the 1000 lumen single, because the three lights are side by side, they dont stack up to get brighter, they just spread out a wider beam, each of 333 lumens.. a close range wall of light that totals 1000 lumens

compared to the triple, the 1000 lumen single will be too bright in the center, so the operator will dial down the brightness to 1/3, to match the brightness of the three 333.3 lumen lights

or

compared to the 1000 lumen single LED, the three 333 lumen lights will look dimmer, and the operator will dial the power up, to increase the LUX and Throw to match the 1000 lumen intensity from a single focused LED

so battery efficiency, longest runtime, will come from a single, not a triple
a triple could actually use triple the power to match the LUX (the visible brightness on target) of a single reflector focused LED

the difference is due to how wide or how narrow, the beams are focused.. and how many lumens each LED is set to output..

 

[Derek Dean]

Jon, maybe I'm wrong, but you seem to be confusing the issue of efficiency with that of perceived brightness, and as far as I'm concerned, they are two different animals.

If you simply limit your discussion to total light output, not perceived brightness, then it becomes obvious when comparing two identical lights using the same LEDs, that the one running multiple emitters will be more efficient at producing an equal amount of light. Yes, that light will be spread out more, and therefore dimmer (although you could possibly negate that with a set of focused lenses), but the total output would be equal, and with less power used to achieve it. The single LED will use more power to achieve the same output, wasting much of it as heat.

Of course I'm no expert, but that seems to me to be what the original poster was asking.

 

[SCEMan]

Trying to locate dog leavings with a thrower is like looking at Google Earth through a straw; trying to defeat inverse-square with brute-force flood snaps the pupils shut with foreground light thus something 100 meters away is more difficult to see than that same cd/lux at 100m away would be in isolation.

That's why I use a flip-up diffuser on my Acebeam L-16.

 

[idleprocess]

both are true:
2. Im also saying that a triple will use batteries faster, because it works harder, to cover a wider area

At optimal range and assuming no power limits are hit, a triple flooder and a single thrower might illuminate a similar size area at similar lux. If the size of the area and the lux values are identical then the lumens are also constant. And the single will be consuming more watts since that's just the invariable physics of LEDs.

But you're talking about markedly different areas and lux values in your example which breaks use cases. Using some arbitrary figures let's say we want to produce 100 lux at 2 meters and at 100 meters, same size area at each distance.

• Single-emitter source optimized for 100 meters : at 2 meters unadjusted it produces an order of magnitude more lux than we want. We can dial it down to 100 lux and then scan the area over time. We can dial it up until the presumably >30 degree spill approaches or hits 100 lux over the target area at terrific power expense and we're throwing away most of the output since the hotspot is too intense. We can also diffuse or re-focus output to spread beam until it reaches the same lux, but we're back at driving a single emitter harder than multiple emitters because constant lumens.
• Multi-emitter source optimized for 2 meters : at 100 meters it produces an order of magnitude less lux than we want. We can crank it up to some improbable level of output to achieve 100 lux, but the power requirements will be unreasonable and we're also flooding the foreground with unwanted light well above our desired lux level. We could focus the individual beams tighter until it's the correct size, however this generally takes inconveniently large optics.

I'm using constant lux over a constant area because that's how I find myself using flashlights. The multi-LED Flashlights I have produce satisfactory lux levels at nominal output at close range while single-LED throwers do the same at long range. Smashing turbo at ~2m with the ~4300lm D4 will contract one's pupils - but less so than doing the same with the D1S at a mere ~1300lm (I can only imagine how much worse the D1S would be at 3.3x more output) and scanning an area with the light dialed down low is time-consuming + distinctly unsatisfying. Similarly, I can only push the D4 out to ~30m and almost have to shield my eyes from the horizon if I want to actually see what it's illuminating that far and forget making it go as far as the D1S can.

That's why I use a flip-up diffuser on my Acebeam L-16.

My primary use cases being indoor tasks, outdoor tasks on my ⅛ acre suburban lot, and walking the dogs on 2m leashes through the neighborhood I've got a number of triples and quads - the right tools for the job. My throwers only see occasional use at the folks' house in the country - and surprisingly little at that since sightlines are generally no more than 100m.

In fact the beams on the reflector triples I've got (old mod'edmaglite, more-current Mini TN30) have considerably more reach than ubiquitous TIR triples and quads. But nothing like single-emitter lights with optics only marginally larger than any single cup in a multi-LED TIR.

 

[LEDphile]

maybe an example will help pretend I have 4 identical lights, each capable of two modes, either 333.3 lumens, or 1000 lumens... 1. pretend I use three lights, each with one LED, set to 333.3 lumens, and I tape them together into a triple bundle. each of the triple lights is producing 333.3 lumens, so three of them add up to 1000 lumens. But the Throw and Lux dont go up by 3x, because the beams are not focused together. 2. I use the other light with one LED, set to 1000 lumens, with a typical reflector with hotspot and spill. the three light bundle will obviously be dimmer than the 1000 lumen single, because the three lights are side by side, they dont stack up to get brighter, they just spread out a wider beam, each of 333 lumens.. a close range wall of light that totals 1000 lumens compared to the triple, the 1000 lumen single will be too bright in the center, so the operator will dial down the brightness to 1/3, to match the brightness of the three 333.3 lumen lights

This is not the case if you are far enough from the lights that the beams overlap. How far from the source this is depends on the beam angle involved, but the principles hold true for all beam angles. Building on your example, let us assume that your 4 lights each project a 10 degree beam that has a sharp cutoff at the edges and is perfectly flat across the beam. At 100', each light gives a 17.5' diameter spot. Since lumens are illuminance divided by area, the spot from the 1k lumen source is at 4.4057 footcandles. Now, if we assume that the 3 identical 333.3 sources are all aimed parallel to each other, and are in a line with the sources spaced by 2" (so the sources are at 0", 2", and 4"), we can approximate the resultant beam as an ellipse with a major axis of 17"10' and a minor axis of 17'6". Dividing the 1000 lumens from the 3 sources into that area gives a illuminance of 4.1998 footcandles, or a difference of just under 5%. That's almost impossible to see under ideal conditions, and with real beam shapes the difference is going to be even less pronounced. And the difference gets even smaller as the distance from the source increases. When one considers that the efficiency improvements from running LEDs at lower currents are real, and that there may also be driver efficiency improvements from running the LEDs at higher voltages (potentially 3x the driver voltage for the triple), it's pretty easy to overcome that 5% difference in illuminance even if the power to the LEDs is the same.

 

[orbital]

+

Die size/area is a factor also.

Take a big 70.2 emitter & drive that at 1A
Now take a quad setup w/ sat xp-g emitters,, and only allow 1A to those 4..

Which do you thing will generate the most lumens.

I'll put $5er on the 70.2

 

[Fireclaw18]

When we talk "efficiency" for LEDs we're generally referring to how much light the LED produces for a given amount of power. Typically for flashlights that would be measured in lumens per watt.

The general rule for LEDs is that they tend to be more efficient when run at lower power. At higher power, a larger percentage of the power input into the LED is expended as waste heat rather than light.

Multiple LED lights are generally more efficient than single emitter lights provided they have:
* the same LED, just more of them
* the same driver (the circuitry that connects the battery to the LED).
* the same battery
* the same total output power from the driver to the LED or LEDs
* the LEDS are not operating at maximum possible power

Since the power has to be split among many emitters, each LED tends to get less power. The result is efficiency tends to go up.

But note that there are many caveats. Every multiple emitter light is not more efficient than every single emitter light. A single emitter light with a very large and efficient LED, like a CREE XHP70, may be more efficient than a small triple emitter light with 3 crappy Latticebright XPG clone emitters.

Also, for lights using FET drivers and very low resistance cells efficiency might be similar at turbo. On the best possible cells, at turn-on on turbo an Emisar D4 might have similar efficiency to an Emisar D1. This is the case if the driver and cell are capable of supplying the same current to each emitter whether its 1 emitter or 3 or 4.

Note however, that while efficiency at turbo might be the same, the multi-emitter light will produce far more lumens, due to the extra emitters. And when each light is set to produce the same amount of lumens, the multi-emitter setup is more efficient. Also small multi-emitter lights run at very high power (like an Emisar D4 or FW3A) will get hot very fast. Depending on how the driver is programmed, they may then ramp down output rapidly to reduce heat. A similar size single emitter light using the same emitter usually pulls far fewer watts and generates less heat. Result is the single-emitter light might take far longer before it ramps down.

Output v. Throw
This is what Jon Slider was talking about.

The total light output of an LED is measured in lumens. You can compare the lumens of different flashlights in your home using the "integrating bathroom" method. Go into your bathroom with a flashlight in each hand. Hold them over your head and point them at the ceiling. Tilt your head down and look at your feet. Turn each light on and off and compare how bright they make the floor near your feet look. Since the hotspot of each flashlight is not in your field of view, what you're looking at is a diffuse reflection of the total light output of each light. The one that makes the floor look brighter has more lumens.

Throw is how far away the light can be used to illuminate things. It is measured in lux. This is a measure of how bright the hotspot of the light is at its center. The main factors for determining throw are the width of the flashlight's head, and the intensity of the LED (think of intensity as lumens per square mm).

Single emitter lights usually have more throw than same-sized same-emitter multi-emitter lights. This is because:
* the width of the head of those lights is same, but the multi-emitter optic or reflector tends to have dead space in it not present in the single-emitter reflector.
* most multi-emitter lights can't sustain as much power to each LED as a single-emitter light can to its single LED. More power means higher intensity.

Result is a single-emitter light will often be throwier than a similar multi-emitter light, but tradeoff is less efficiency, smaller hotspot, and less max output.

Personally, I prefer multi-emitter lights for up close use due to their massive output and wide hotspot. It can be a great benefit to see a wide area up close. However, for seeing stuff outside at long-range a single-emitter light is almost always the best choice.

 

[Derek Dean]

Very well put, Fireclaw18. The original poster's questions doesn't really have a one-size-fits-all answer, because it depends on many variables.