D. Peter Maus wrote:
On 8/9/13 18:48 , Joe from Kokomo wrote:
On 8/9/2013 2:33 PM, D. Peter Maus wrote:

So far, I"m getting the equivalent of 75w incandescent light out of
one 8.5W LED lamp.

The URL/ ad that you quoted said:

Stock Code: ETI-520163MD
8.5 Watt - LED Light Bulb - Omni-Directional A19 - 3000K Warm White -
600 Lumens - 50 Watt Equal

They advertise it a 50 watt equivalent but you are saying it's the same
as 75 watts. If it really is close to 75, one would think they would not
be shy and call it 75.

Are you actually measuring the lumen output or just "eyeballing" it? Do
you have higher than 'normal' line voltage?

Not pickin' on ya, D.P. It's just that inquiring minds want to know why
the difference. :-)


Dial it back, Joe.

I did mention that I used a light meter to measure the output. Were
you not reading?

My understanding is that a lumen is not directly a measure of
output power. It is modified by a weighting curve, I believe,
to reflect our eyes' varying response to different wavelengths.

So you need, of course, a light meter that reads true lumens,
not just power output (energy per unit time).

But I agree with your statement below that they may be quoting average
output over the rated life of the device.

White LEDs do not directly produce light, like a single color LED.
They produce a wavelength and expose it to a phosphor which causes the
phosphor to flouresce. Since that's a ablative process, the output of a
white LED diminishes over time, depending on how hard the phosphor is
worked.

Here's some info, albeit somewhat technical:

http://www.digikey.com/us/en/techzon...of-fading.html

I had no idea that the process involved the additional step. Nor did
I realize that fading might occur, caused by crystalline imperfections
that grow worse over time.

This article claims that the band gap is such that the naturally
produced radiation is towards the short wavelength end of the
visible, and that the fluorescence (phosphorescence?) adds in
the longer wavelengths so that the resulting radiation appears
white, i.e., distributed more uniformly across the visible
spectrum.

George

White LED lamps are correctly rated at an average luminary output over
time.

I'm at the beginning of these lamps' life cycle. So output is higher
than rated.