Lumens vs perceived lumens, is there a formula?

Actually I don’t care anymore. 50% mode looks the same as 100% to me so I’m just going to stick with mode 8 where 50% is the highest. Now I’ll get longer runtimes and not burn my hand, win win

Our perception of lumens isn’t linear. I find that to perceive a light that is twice as bright, you need a luminous increase to a factor of four. ie, for 250 lumens to seem twice as bright you need 1000 lumens. To seem twice as bright as a D4V2 ~4000 lumens, you need 16000 lumens etc

So using that formula, if a light is 1600 lumens at 100% and 800 lumens at 50% then it should seem 25% brighter to the eye when going from 50% to 100% right? It doesn’t feel like that’s the case with mine.

50% and 100% of what though? Amps? If so then it’s not quite as simple as that. An LED gets less efficient the harder it’s driven. For instance if an LED produces 1000 lumens at 5 amps, it won’t produce 500 lumens at 2.5 amps, more likely to be ~700 lumens.

That makes sense, I wish so had one of those things that can test output

I have one of these that seems to be working well - https://www.amazon.co.uk/dp/B006QHOX0Y/ref=cm_sw_r_cp_api_glt_fabc_WWVHS8R4352RRV92TBZH

If you step outside and put the light on something 100 meters away you’ll see the difference very easily between 50 and 100%. Inside the house, it may be harder to tell.

Calculating throw from candela = 2 * square root of candela. Therefore the quadrupling of candela to double throw would make sense.

Does this carry over into overall brightness / Lumens as well? I suspect yes, because the surface area of the inside of a sphere is a square function as well.

I am sure someone smarter than I will be along shortly to answer.

You don’t see lumens, you perceive lux.

Presumably that only measures lux not throw as well?

You can only ever measure lux. You then use a formula, or enter the numbers (Lux and distance from the meter) into a calculator to work out throw. I use this one - Lux to candela (cd) conversion calculator

I just hold the light to my ear on turbo and check my opposite ear with a light meter. :wink:
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Just joking, but when I check a light for throw, the perceived brightness on the wall and using it a night are the most fun for me. I can see the difference between 4000 and 6000 lumens. It appears the more you use different lights, the easier it is to differentiate lumens.

Well I’ve ordered one of those light meters, what’s the recommended measuring distance to accurately estimate throw?

Depends on the light intensity and the range of your meter, usually 1-10 m. In extreme cases you can add a ND filter and correct the measurements afterwards.

Well I still have a Fenix light with known throw, presumably if I measure that and compare it Fenix’s own measurements then I should be able to figure out the margin of error

Not quite. You need a calibration light (the Fenix in your example) when you come to measure lumens, either through ceiling bounce, sphere or tube. But when it come to candela, it’s purely just numbers. I predominantly use around 6m to measure. So I set my meter up, choose the range (x10, x100 etc), measure the distance with a laser measure, then take a reading. Enter these numbers into the calculator I linked to above and it will give you your candela. Then I square root that number and x2 to get meters of throw.

you may just have a weakish battery
sometimes the bat cannot do what the light could do

and 50% more is not that apparent, either ,as others said

Fair pointed but I was testing with a fully charged battery. I’ll try the same test again outside when it’s dark when I have a chance, see if the drop in throw is noticeable.

The longest distance in my house is 6.46 meters so I use this for throwers.
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Reading X 6.46 X 6.46 = Candela/CD.
Throw = Square Root of 4 X CD, all in meters.
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Same answers as above.
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Presumably you have to do this test in complete darkness?