.25 lux at 400 metres = 50 lux at ?? metres

rufus001 · May 17, 2012

Sorry for the bizzare title and no idea if this is the correct place to post this question. Basically I've seen the reviews that specify how far a light can throw .25 lux(moonlight). But as I was researching the subject I discovered the 'average' lux in an Aussie living room is 50. Well at least according to wikipedia. So I was wondering how I can convert .25 lux distance of throw to a 50 lux distance of throw. So if the hotspot is moonlight lux at x metres the hotspot is Aussie living room lux at x/whatver. Or ideally any lux to any lux. Anybody know a simple formula?

Kitchen Panda · May 17, 2012

rufus001 said:
Sorry for the bizzare title and no idea if this is the correct place to post this question. Basically I've seen the reviews that specify how far a light can throw .25 lux(moonlight). But as I was researching the subject I discovered the 'average' lux in an Aussie living room is 50. Well at least according to wikipedia. So I was wondering how I can convert .25 lux distance of throw to a 50 lux distance of throw. So if the hotspot is moonlight lux at x metres the hotspot is Aussie living room lux at x/whatver. Or ideally any lux to any lux. Anybody know a simple formula?

The relation between lux and distance is an inverse square. Half the distance gives four times the illumination on the surface (lux). So .25 lux at 400 metres is 1 lux at 200 metres, 4 lux at 100 metres...etc. Blowing the dust off the slide rule I get 50 lux at 28 and a fraction metres.

(And there must be a "LIght measurement 101" thread here somewhere that explains this better.)

Bill

eh4 · May 17, 2012

.25 @ 400

power law roughly stated for radiation:
'quadruple the power to deliver same power at double the distance'.

so working backwards:

1 @ 200
4 @ 100
16 @ 50
64 @ 25
256 @ 12.5
1028 @ 6.25
4112 @ 3.125
16448 lux @ 1.5625 meters

64 lux at 25 meters is pretty close.

Here's the requisite wiki: http://en.wikipedia.org/wiki/Inverse-square_law#Light_and_other_electromagnetic_radiation

rufus001 · May 17, 2012

Thanks guys!

Robin24k · May 17, 2012

ANSI FL1 Beam Distance is calculated using the following formula: Beam Distance = √(Peak Beam Intensity/0.25).

If beam distance is 400 meters, that means peak beam intensity is 40,000 candela. Using the formula with 50 instead of 0.25, you'll get 28 meters for beam distance to 50 lux.

.25 lux at 400 metres = 50 lux at ?? metres

rufus001

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Kitchen Panda

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eh4

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rufus001

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Robin24k

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