BillBill
Newly Enlightened
Single LED lights can produce up to three lumens. However they're overdriven. How many lumens would a good 5mm white LED produce? Does it vary a lot?
How many lumens is a white 5mm LED?
- Thread starter BillBill
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The_LED_Museum
*Retired*
Very few of us here on CPF are equipped to measure in lumens.
You need an expensive instrument called an "integrating sphere" to do that.
I believe one, possibly two people on this BBS have access to an integrating sphere on an irregular basis.
Most light measurements of LEDs here are done in mcd (millicandelas) and lux.
mcd is measured by placing the LED 12" from a light sensor, setting the light measuring instrument to read in candelas, and multiplying the reading by 1,000; and lux is measured by placing the LED one meter from a light sensor and setting the light measuring instrument to read in lux.
The Wavetek Meterman LM631 is a popular light measuring instrument here on CPF, and a number of CPFers have this instrument. It can read in candelas or lux, but not in lumens. An integrating sphere does that. /ubbthreads/images/graemlins/jpshakehead.gif
You need an expensive instrument called an "integrating sphere" to do that.
I believe one, possibly two people on this BBS have access to an integrating sphere on an irregular basis.
Most light measurements of LEDs here are done in mcd (millicandelas) and lux.
mcd is measured by placing the LED 12" from a light sensor, setting the light measuring instrument to read in candelas, and multiplying the reading by 1,000; and lux is measured by placing the LED one meter from a light sensor and setting the light measuring instrument to read in lux.
The Wavetek Meterman LM631 is a popular light measuring instrument here on CPF, and a number of CPFers have this instrument. It can read in candelas or lux, but not in lumens. An integrating sphere does that. /ubbthreads/images/graemlins/jpshakehead.gif
Top numbers for white LEDs are 20 Lumens/watt. Since a 5 mm part *at spec* (20 mA at say 3.6 Volts) is about .07 Watts, the best of 'em is about 1.5 Lumens, say two if over driven to 30 mA or so.
A Craig points out, you'll have some troubles proving it, however.....
Doug Owen
A Craig points out, you'll have some troubles proving it, however.....
Doug Owen
idleprocess
Flashaholic
There are equations you can use to approximate lumens from mcd if the nominal beam angle is known - best I've seen for 5mm LEDs is in the area of 1 lumen.
There are 2 commonly used formulas - one is generally better for lambertian (wide-angle) sources, the other is better for point (narrow angle) sources. Both are in a post titled "candles vs watts" in general light discussion.
Small imtegrating sphere are actually not too terribly expensive - I've seen them in the neighborhood of $500 for ~12" (~300mm) or smaller diameter models optimized for measuring directional light sources (such as LEDs).
There are 2 commonly used formulas - one is generally better for lambertian (wide-angle) sources, the other is better for point (narrow angle) sources. Both are in a post titled "candles vs watts" in general light discussion.
Small imtegrating sphere are actually not too terribly expensive - I've seen them in the neighborhood of $500 for ~12" (~300mm) or smaller diameter models optimized for measuring directional light sources (such as LEDs).
