If one brand flashlight = 200 lumens, then would 2 lights = 400 lumens?

OK, sorry for the generally unenlightened question, but I was wondering about something...

If you had one flashlight that gave an output of 200 lumens, then would having 2 of the same flashlights on at the same time = 400 lumens? Is calculating the total lumen output as easy as adding the lumens from one light + lumens from another light?

Yep. Lumens is a measure of total output... like taking the whole beam and stuffing it in a box and measuring it. That's how it's done actually, in a device called an integrating sphere.

That's how I understand it.

Note however, human eyes responds to lumens logarithmically; hence 400lm is not perceived to be twice as bright as 200lm by human eyes.

I thought than when measuring incandescent household bulbs that two 50w lights give off less light than one 100w light. Is that wrong?

greenlight said:

I thought than when measuring incandescent household bulbs that two 50w lights give off less light than one 100w light. Is that wrong?

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That's a matter of efficiency. It's higher at higher watts. For hid and incan.

Yes, thats how it works.

Sometimes I bring a 6P (~200L) and 501B (~140L) out on night hikes for almost 350L total. One light in each hand:thumbsup:

But the added light really only amounts to a "little" more.

Is it not square root of 2, ie 1.414 times?

Perceived, or measured.

abvidledUK said:

Is it not square root of 2, ie 1.414 times?

Perceived, or measured.

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No.

Lumen is a measure of overall output, and is a scalar quantity, since it is effectively integrated luminosity.

Perceived brightness is a physiological function, and is (like all physiological functions) a logarithmic value.

greenlight said:

I thought than when measuring incandescent household bulbs that two 50w lights give off less light than one 100w light. Is that wrong?

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Wattage is not equal to Lumens but simply a measure of how much power the bulb consumes. You are correct that one 100 watt bulb generally gives off more light than two 50 watt bulbs. Doubling the wattage of even a single bulb will not necessarily give you double the Lumens.

and if you quantify the scalar function of the non-corporeal viscera, it becomes immediately apparent that the tangent line lies directly opposite the manufactured impedance. hence, all things are relative!

rainbowbright said:

If you had one flashlight that gave an output of 200 lumens, then would having 2 of the same flashlights on at the same time = 400 lumens?

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OOOHHH YEEEEAAAHHH

abvidledUK said:

Is it not square root of 2, ie 1.414 times?

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No, you've ghot it confused with the hypotenuse of a right triangle. A common error.

kurni said:

Note however, human eyes responds to lumens logarithmically; hence 400lm is not perceived to be twice as bright as 200lm by human eyes.

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It's better to think of logarithmic sensitivity as something that relates 3 or more brightness levels rather than just two.

To me, 400 lumens really does look a lot brighter than 200 lumens. But the important factor here is that the brightness was doubled, not that it was increased by 200 lumens. If we then go from 400 lumens up to 600 lumens, this second increment will seem less significant to the eye than the first one. You would actually need to go up to 800 lumens to get the same perceived change.

One rule of thumb used on CPF is that you need a doubling of brightness for your eyes to see this as a "significant" change. I've found that for practical utility in a flashlight, an increase of 4X or more is best.

A design flaw in many 2-level lights is that the high and low beams are too close in output. Contrast this with a well-designed light like the Surefire L1, where the high is 8X as bright as the low.

Everynight, I use 2 Fenixs (TKs) to brighten up the room when catching/zapping mosquito. 2 lights are better than one to increase the chance to catch them.

The effect of 2 lights ON at the same time provides more spread/flood plus overall brightness(perceived or otherwise). The proof is in the KILLing of mosquito per night.

Of course, sometimes, a Mosquito are smarter than 2 LEDs + 1 CPFer (1 M >> 2 Leds + 1 CPFer).:mecry:

meuge said:

No.

Lumen is a measure of overall output, and is a scalar quantity, since it is effectively integrated luminosity.

Perceived brightness is a physiological function, and is (like all physiological functions) a logarithmic value.

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man, do i feel dumb. i have no engineering or technical background at all (but im trying my best to learn) are there any threads that can give a wanna be a flashaholic some badly needed information so that i can learn???