how to measure lux from a ledlight

[gravityz]

did some searching but could not find anything

can anybody tell me how to measure the lux amount coming from a ledlight?

should i just point the hotspot to the luxmeter from a distance of 1 meter?
should i use the ceiling methode or should i build it into a cartonbox(and if so will the light be shined directly to the senso or indirectly.

it is not so much that i need an accurate reading but i like to have a way to compare lights in an objective manor.

thanks

 

[Kilovolt]

I am too lazy to build a lightbox so I just shine the beam into the cell of a luxmeter from a distance of 1 m. I have in my kitchen a wall that is just 1 m tall so I put the meter on the floor and keep the flashlight in my hand with the arm resting on the said wall.
There no scientific purpose in my measurements but at least I can compare one light with another and different types of batteries in the same light.
BTW with a lightbox you could estimate lumens i.e. capture the whole amount of light coming out of the lens but then you would have to make some assumptions to calibrate the whole setup.

 

[Nake]

Here's a link to building a lightbox. I use one like this myself.

http://www.flashlightreviews.com/features/lightbox_output.htm

 

[gravityz]

Thanks

very helpfull

i think comparing crees to crees or SCC's to SCC's you can use the direct methode.

if i have time i will build that milkcarton box.
i have aluminum tape so that should be easy

 

[precisionworks]

I just ordered a 12" hollow styrene sphere from Barnard Ltd. in Chicago. $38 including tax and shipping. Should be easy to make an integrating sphere with that.

http://barnardltd.com/product.jsp?prodId=1878&catId=628

Also, the lowest price I found for a quality meter is $88 for the ExTech EA31 from Test Equipment Depot:

http://www.testequipmentdepot.com/extech/lightmeters/ea30.htm

 

[Curious_character]

To measure the lux from a light, you just point it at the lux meter. The reading is the lux value. Most people want to know the illuminance in candelas, which is the lux at one meter, at the brightest spot. To measure that, put the light one meter from the lux meter and point it so the reading is maximum. This is an indication of the light's "throw", or how far away the light will illuminate an object at some brightness level. If you take the square root of the candela measurement, you'll have the distance, in meters, at which the light will illuminate an object at one lux.

A light box measures the total light output, which is something else. Although it typically uses a lux meter, the result is proportional to the number of lumens the light produces, not what the lux level would be at any particular distance or how far away the light will illuminate an object. Determining the number of lumens that corresponds with the light box lux reading requires finding a conversion factor. I've calibrated mine by measuring a number of LEDs of known bins running at a known current.

c_c