Define:lumen

Pawnless Endgame

Pawnless Endgame

Pawnless Endgame

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Inspired by the recent LED torch thread, I'm asking how lumen is quantified and how it relates to incandescent, CFL and LED bulbs at given wattages.

Define:lumen on Google returns The SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform...

The Wiki article gives you one example, where it says that a 23W CFL (which is your average 100W incandescent) emits about 1500-1600 lumen, so I'm guessing that ~1500 lumen is your average household bulb? Then a bathroom with 3 x 100W spots is ~4500 lumen?

Cheers :-)
 
Doesn't it depend where you measure from or something or how focused the beam is?

My 1200 lumen bike light thing is certainly brighter than a household bulb for sure.
 
Welshy said:
If I remember rightly, 1 lumen was (originally) equal to the amount of light emitted by a candle.
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+1

I thought it was the amount of light from 1 candle on 1 square meter from 1 meter away

(but there could be a modern version)
 
Think it's measured a certain distance from source, as the lumen output is lower the further away you get.

Wattage is just how much power is consumed so you need to look at the ratio of lumens at distance X Vs watts consumed to quantify how efficient a light source is.

You can't use watts alone to compare say, led with florescent or halogen. Halogen spot lights for example is very bright but also very inefficient.


Also colour temperature comes into play depending on what the lightens used for.
 
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Jonny ///M said:
Doesn't it depend where you measure from or something or how focused the beam is?

My 1200 lumen bike light thing is certainly brighter than a household bulb for sure.
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mattyfez said:
Think it's measured a certain distance from source, as the lumen output is lower the further away you get.
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No, that's Lux.

Lumens measures the total amount of light emitted from a light-source in all directions, which is why the only way to accurately measure Lumens is with a device called an integrating sphere.

Lux measures the brightness per unit-area, which is why some less-than-reputable torches are given with their brightness stated in lux. The Lux-Measurement can be altered by moving the sensor closer to the light source, which concentrates light from a large area into a smaller one, raising the measurement. Torches which throw a very tight directional beam also score very high lux-measurements even though the total light output might not be very high at all.

Lumens is a "Truth-Friendly" unit, in that when all the ratings are honest (they aren't, i'm afraid though), one can conclusively say that a light with 200 lumens is brighter than a light with only 100 lumens. However, a light with only 100 lumens that projects a very tight beam will appear to be much brighter than a light that emits 200 lumens but in a very wide beam.

This is why my 150-lumen backup torch looks to be about 50x brighter than the 3000 lumens of room-lights that I have, because their light is spread in all directions throughout the room, and the torch is shining it's light over a very small area.
 
Aod said:
No, that's Lux.

Lumens measures the total amount of light emitted from a light-source in all directions, which is why the only way to accurately measure Lumens is with a device called an integrating sphere.

Lux measures the brightness per unit-area, which is why some less-than-reputable torches are given with their brightness stated in lux. The Lux-Measurement can be altered by moving the sensor closer to the light source, which concentrates light from a large area into a smaller one, raising the measurement. Torches which throw a very tight directional beam also score very high lux-measurements even though the total light output might not be very high at all.

Lumens is a "Truth-Friendly" unit, in that when all the ratings are honest (they aren't, i'm afraid though), one can conclusively say that a light with 200 lumens is brighter than a light with only 100 lumens. However, a light with only 100 lumens that projects a very tight beam will appear to be much brighter than a light that emits 200 lumens but in a very wide beam.

This is why my 150-lumen backup torch looks to be about 50x brighter than the 3000 lumens of room-lights that I have, because their light is spread in all directions throughout the room, and the torch is shining it's light over a very small area.
Click to expand...

Oh aye it's Lux, how could I forget that :(

So Lux is basically the PMPO of the lighting world and is used to sell crap.
 
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