voltage & lumen question

sort of new ay yhese led lights, voltage question, lets say a light operate at 2.7 to 4.1 volts is it correct that my light will be as bright at 2.9 volts as compared to a battery with 4.1 volts.

lumens question I purchased a new light and got it today specs say it is 530 lumens with a single 18650 battery, i did not get it out at night yet but in my basement when this new light on high does not seem to be nowhere as bright as my 200 lumens Sirefire G2X, can it be the new light has a different reflector for more flood type light. not really impressed unless I am missing something. but I will find out tonight.

Chet

Chet said:

sort of new ay yhese led lights, voltage question, lets say a light operate at 2.7 to 4.1 volts is it correct that my light will be as bright at 2.9 volts as compared to a battery with 4.1 volts.

lumens question I purchased a new light and got it today specs say it is 530 lumens with a single 18650 battery, i did not get it out at night yet but in my basement when this new light on high does not seem to be nowhere as bright as my 200 lumens Sirefire G2X, can it be the new light has a different reflector for more flood type light. not really impressed unless I am missing something. but I will find out tonight.

Chet

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Hi Chet,

Q1

www.candlepowerforums.com]Ceiling [/url]bounce to compare lumen output instead of lux. Yes, the Surefire probably throws a brighter spot (Higher lux value) than whatever light you have.[/url]

Flashlights can have several state lumen values.

1. Actual output with partly-used batteries.
2. Output with super-fresh batteries.
3. Light that should come from the emitter at the driver's actual output.
4. Light that could possibly come from the emitter if it were driven at absolute maximum current.

Be suspicious of neat round numbers like 530, especially if they neatly match up to brightness ratings from Cree.

Voltage is not necessarily related to brightness. It depends on how the light is driven. Brightness is determined by the current through the LED. In a direct-drive circuit, it is equivalent of driving the battery through a resistor, then the LED. The voltage across the LED should be constant, but the voltage across the resistor will change. As the battery gets weaker, it's voltage lowers, which means the voltage drop across the resistor must lower, which means less current and less brightness.

If you have a current driver circuit, then it will maintain a constant current to the LED, which would give a constant brightness (assuming temperature didn't change). Some lights use a current drive, some are direct drive so the answer is: it depends. Do some searching in the flashlight parts forum and you should get some good info there.

As far as one light seeming brighter than the other, you can't compare lights by using their beams. A floodier light will appear dimmer than a throwy light. Do the ceiling bounce test to compare light output.

It is VERY difficult to visually compare the "brightness" of lights with different beam patterns....a "hot spot" typically overwhelms our eyes exposure limits for example, so some lights with tight beams, after that point, will seem to have the same "Brightness", because both are over range for us to resolve...and, ironically, the LESS tight beam may even look brighter as the "hot spot" will appear larger.

If the beam was projected onto a surface that covers twice the area, it would have to be twice as bright to look the same in brightness....because the lumens are more spread out, so you need more of them to have the same lux on the surface of your target.

This is why a light meter is useful...and why the above ceiling bounce test is useful...it helps to homogenize the beam's light, so that lights with two dissimilar beam patterns can be compared.

Floody lights need a TON more lumens to look "Bright" than throwers do.

1,000 lumens projected onto a square meter of target will yield 1,000 lux...which looks VERY bright. Office lighting for example is typically at ~ 200-300 lux for perspective.

If you make that same beam floodier, and use those 1,000 lumens to light a 10 square meter target, it will only yield 100 lux, a LOT dimmer visually.

The thrower makes a small hot spot that makes you squint because "its so bright", while the same amount of lumens spread out makes a dim pool of light that is not even as bright as your average desk at work looks, etc.


So, you shine 1,000 lumens of a focused tight beam on a target, and it looks very "bright", but 1,000 lumens of flood looks dim. You'd need to learn to "Integrate" the total light, to be able to make a good guess as to how "bright" a light is by just shining it at something.