Lumen question: If you point two 60 torch lumen lights at wall = 120 lumen light?

General question ...

I have a surefire L1 and E2L ... both 60 lumens (lets round). I was playing with them the other night on a walk and I got thinking ... if I lay one light hotspot right on top of the other is this what 120 lumens looks like?

I ask because both lights are respectably bright, but if thats what 120 torch lumens looks like I was underwhelmed ... it appeared only marginally brighter.

This leads me to think I should be perfectly happy with a 60 lumen light.

i think you are still looking at 2 60 lumen hot spots, it's just that one of them is now shining at a very bright wall.

Fooboy said:

General question ...

I have a surefire L1 and E2L ... both 60 lumens (lets round). I was playing with them the other night on a walk and I got thinking ... if I lay one light hotspot right on top of the other is this what 120 lumens looks like?

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Yes, you can simply add lumens. Lumens are a measurement of the total radiated power from the light-source (not to be confused with the input power) weighted by how sensitive the human eye is to the wavelengths emitted. This means UV and IR are by definition zero lumens no matter how much you have, and colors that the eye is more sensitive to, contribute more to the apparent brightness/lumen total.

I ask because both lights are respectably bright, but if thats what 120 torch lumens looks like I was underwhelmed ... it appeared only marginally brighter.

This leads me to think I should be perfectly happy with a 60 lumen light.

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This is because the eye has a logarithmic response to illuminance, which is measured in lux (lumens per square meter). That's how your eyes can function in situations as extreme as bright sunlight (100,000 lux) and half-full moonlight (0.1 lux), a million to one difference.

You will find however if you were to point those lights at a target that was fairly far away, and not right at your wall, that you'd notice a much bigger difference between 60 and 120 lumens. Beam pattern matters here, too. If you have a bright hotspot in your field of vision, your pupils will tend to constrict. If you were to do ceiling bounce with those two lights, and not look directly at the light, you should find the difference more noticeable there, too.

yup, what he said....i think i asked this question was also asked before though, although i dont remember which thread...

it is also worth taking note that a 120 lumen light might have a very differnt beam pattern from the 2 you have. That being the case, it might look like a whole lot more light because of the spill..etc.

Crenshaw

Good question & some great info as well !

Here is a simple test. Take two cars of the same make and model and point the lights of both at the same target. Then turn the lights off of one them. You might notice a small difference in light. Then turn the high beams on one car. You WILL notice a BIG difference.

What does this test prove? How do we know that the high beams are 2x and not 10x the lumens of the lows? Not to mention that high and low beams are designed with different patterns for a purpose.

KuoH

KingGlamis said:

Then turn the high beams on one car. You WILL notice a BIG difference.

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trinity nailed it!

that's exactly it, doubling your lumens appears as nothing significant to human eyes.

It's why I'm always trying to get people to stop fretting about slight differences in rated output between different lights on the market, but instead, choose a ballpark range of lumens desired, then pick the flashlight based on the design, function, runtime etc. Picking the proper beam for the task at hand will have a much greater effect on usefulness than the lumen rating. A ~200 lumen LED thrower can be more useful for lighting up distant objects than a multi-emitter setup that's rated 500+ lumens, while even a little 50 lumen floody beam light can be more useful in-doors than a 200 lumen thrower.

KuoH said:

What does this test prove? How do we know that the high beams are 2x and not 10x the lumens of the lows? Not to mention that high and low beams are designed with different patterns for a purpose.

KuoH

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The point is, two low beams = the same light as one low beam. If you point them at the same target the light you see will be the same. But switch to high beam and it will be much brighter.

As others have indicated, your equation is incorrect. The human eye perceives them as almost the same because you don't have manual controls of your pupils like you might with a camera. Try taking pictures of the low beam example and you will be able to see the difference.

Stating that the high beams are brighter without any reference to the measured difference between the two is like saying a POB HID is brighter than a minim*g. Nobody will disagree, but it doesn't prove anything other than the obvious.

KuoH

KingGlamis said:

The point is, two low beams = the same light as one low beam.

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A fun test is to take two identical flashlights, or two very similar flashlights, and combine the beams. When you do this you will double your lumens if each light has the same output. The result, it looks brighter, but it doesn't really look twice a bright. I think I've heard you need 4 times the light to look twice as bright? So you'd need to go from 1 flashlight, to 4 flashlights of all the same output and beam pattern. Then it should look twice as bright from what I understand.

WadeF said:

A fun test is to take two identical flashlights, or two very similar flashlights, and combine the beams.

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I'm sticking to Dr. Venkman's advice here and treating "beams" as "streams" and I'm not going to cross them.

I wouldn't stake my life on it but I would say if you point one light at a wall - take a measurement in the spot and then point a second, identically focused light exactly over the spot of the 1st light and take another measurement, you'd have double the candlepower measurement at the given measured spot. Lumens is a measurement of all light emitted from a source where candlepower would be a measurement of the amount of light at a point in space.

mdocod said:

It's why I'm always trying to get people to stop fretting about slight differences in rated output between different lights on the market, but instead, choose a ballpark range of lumens desired, then pick the flashlight based on the design, function, runtime etc.

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Very good advice :thumbsup: Always consider more than just the output.

Regards,
Tempest

Combining multiple flashlights is one neat way to arrive at a powerful light.
Look at this thread A "three banger" stack of EDC lights! for an interesting demonstration. The weird thing is why so few do this :thinking:
Some rubber grommet spacers and shrink wrap around 3 lights would allow the tail caps to be turned, removed, bezels to be turned and or removed etc., so there is no excuse really

yes
120 lumens

but if you point 2 fenix 60 lumen is it 60 SF lumens?

that idea/test with the low/high beams is quite good:

floody low are way different from focused high,
difference in sheer power is almost nothing - a H4 bulb has 50 Watts low, 55 Watts high, makes 100 W low / 110 W high for a common car (at least around here)

I have two minimags zip tied and taped together with a spacer between them and I have to say in a room with both beams either focused or not, they do not seem much brighter then with only one turned on. However if you take them out side, and focus each beam one at a time for the best focus possible, their throw is greatly increased.

I'll shorten Trinities answer


LUMENS does NOT directly equal Brightness.

Just so I'm sure that I understand it correctly, would it be more correct to say "LUMENS does NOT directly equal perceived Brightness"? While more lumens do not translate directly proportionally to more brightness, it does never the less increase overall brightness, even if it isn't readily apparent to the naked eye.

KuoH

Double_A said:

LUMENS does NOT directly equal Brightness.

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