Rules of Thumb for flashlights -and for other things if you want this thread moved

I just got one that I keep wanting to blurt out while reading numerous threads.

When evaluating a light multiply lumens by runtime to get "lumen X hours", this will let you see the overall efficiency of the light and which levels that the light produces are it's sweet spots.

Also, you could take the same lumen/hours number and divide it by the (voltage X miliAmp hour rating) of the battery chemistry of the light in question to get an overall equivalency between lights.

For example, Zebralight makes the H51Fc which has a sweet spot of lumens/hours at 345LumenXHours at M2 (15 lumens for 23 hours)... Incidently, M1 and L2, the settings above and below M2 are both nearly as efficient at around 336 LumenXHours.

Anyways, take that 345 lumen X hours and divide it by the Watt hours of the cell chemistry to see the overall efficiency of the light... in this case an AA 2000mAh Eneloop with estimated 2.4 Wh gives an overall Lumen X hours / Watt hours score of 143.75

Then the backpackers can divide that number by the weight of the light and battery to get their overall useful light per gram.

That's all I got for now, -other than that if you ever find yourself in need of a very small quantity of high quality machine oil, just rub the part along the side of your nose, just as good as whale oil without the ethical dilemmas.

My favorite rule of thumb regarding LED heat, compliments of McGizmo:

The rule is if it (the light) is too hot for your thumb, it's too hot for the LED.

Easy.

nbp said:

My favorite rule of thumb regarding LED heat, compliments of McGizmo:

The rule is if it (the light) is too hot for your thumb, it's too hot for the LED.

Easy.

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hey that is a good one, I wonder how that applies to when messing with components... I'll have a bare emitter pressed to a heat sink, the heat sink stays reasonable but touching the led itself (yes I'm sure it's not great for the led dome) it's QUITE hot... led continues to function, hour after hour, heatsink stays warm and continues to wick away heat.

eh4 said:

For example, Zebralight makes the H51Fc which has a sweet spot of lumens/hours at 345LumenXHours at M2 (15 lumens for 23 hours)... Incidently, M1 and L2, the settings above and below M2 are both nearly as efficient at around 336 LumenXHours.

Anyways, take that 345 lumen X hours and divide it by the Watt hours of the cell chemistry to see the overall efficiency of the light... in this case an AA 2000mAh Eneloop with estimated 2.4 Wh gives an overall Lumen X hours / Watt hours score of 143.75

Then the backpackers can divide that number by the weight of the light and battery to get their overall useful light per gram.

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Quoted above is pretty much the exact line of thought that first made me consider Zebralights about half a year ago. Having acquainted myself with specs and tests of most of the popular compact lights, I'm still convinced these are the current champions at putting a single cell to useful work until the last tiny drop of juice, be it AA or Li-ion. H502 is probably the single most effective runtime/weight light ever built, even among the dimmer lights; not necessarily most useful for backpacking, though.

Use the low and medium output modes for most tasks. Reserve the high and maximum for critical tasks.

Just because a light is capable of delivering certain amount of lumens doesn't mean that you should be constantly pushing it, just as you wouldn't want to redline your engine every time you drive the car.

Running the light at lower than maximum outputs dramatically increase runtime and decrease waste heat.

If you find yourself needing to use the maximum output modes frequently, it's wise to invest in a light that can cope with it better. For example, let's say that you have a light that can deliver 400 lumens and frequently encounter situations where you need to use that output for extended periods. Get yourself another light that can deliver 800 lumens and have that run at medium output, as it will have the necessary heatsinking to run cool throughout its runtime at that output.

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Floody lights are good for most purposes while throwy ones are more or less specialized for long distance. However, you can easily turn a throwy one into a floody one with the aid of a diffuser or diffusing material; you can't turn a floody one into a throwy one without significant modifications.

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Use quality power source whenever possible. With cheap batteries, you are playing with ticking time bombs, as they may A) fail to deliver expected performance, B) leak acid, or C) vent compressed hydrogen in an explosive manner.

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