# Re: LED Lumens to Lux conversion?

*From*: Nobody <nobody@xxxxxxxxxxx>*Date*: Thu, 15 Nov 2007 19:49:12 +0000

On Wed, 14 Nov 2007 16:50:37 -0800, TazaTek wrote:

I'm trying to pick out some LED's for to make a 10,000 Lux @ 36 inches

(or 1 meter) LED lamp. My problem is that I'm not quite sure of how

to convert the lumens spec on the LED to the Lux to figure out how

many LED's I need to buy.

I know that Lux = Lumens/ m2 , but I'm not exactly sure of how that

applies to something that is 1 meter away, and would be, say the size

of a small book.

The lux depends upon the size of the spot, and thus the illumination

angle. A wide-angle LED will produce a lower lux figure for the same

lumens.

To determine a rough lux value, divide the lumens figure by the area of

the LED's "spot". E.g. for even illumination over a 90-degree (+/-

45-degree) cone at 1 metre, the spot radius will be 1m*45*pi/180 ~=

785mm, and the area will be ~1.94 square metres, so lux ~= lumens/1.94.

If the "size of a small book" refers to focusing the entire output of

the LED on a small area, then the only factor is the area on which you're

focusing it, not the distance (obviously, you'll need to narrow the angle

as the distance increases to keep the smaller area).

E.g. if you're focusing on a 10cm square, lux = lumens / 0.01, so you

would need 100 lumens to get 10000 lux.

.

**Follow-Ups**:**Re: LED Lumens to Lux conversion?***From:*TazaTek

**Re: LED Lumens to Lux conversion?***From:*Bob Myers

**References**:**LED Lumens to Lux conversion?***From:*TazaTek

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