Measure Light Output At a Distance = M - LOAD

I had a thought about measuring output from flashlight at a distances greater than one metre. I plan on doing some tests using a 40W solar panel about 600mm square, this might give a better comparison of throw. The panel will be at 100 metres (untried yet) an ambient Voltage measurement taken and then a measurement of the flashlight, I then subtract the ambient measurement from the flashlight measurement to give me a figure less influenced by the ambient light level.

What do you think? Will it work? Does anyone have a good acronym?

Your thoughts please.

Norm

Realistically, that's probably how a lux meter works in the first place.

It would offer a bigger target, though.


The other issue might be the light spectrum. Would a High CRI light excite the PV cells more than a normal light?

I had thought of those things Simon, just tossing around ideas. I appreciate your input. Just trying to compare larger lights, beam shots are sometimes hard to differentiate.

Norm

Its a thought at least. The lux meters we currently use are not optimized for LED lights either for example, so it may be a simple matter of calibration.

If you are counting on the panel being ABLE to absorb all of the energy, assuming a known conversion efficiency, etc...it should be doable...even w/o the meter space.

For example, putting the light bezel down onto the panel and turning it on should give the same thing if the surface area of the panel hit by the light is able to absorb it all.

If the light emits too much for its "Bezel print" to absorb, then backing it up to make a wider circle of light on the panel until it CAN absorb it, yet loose no spill to the sides of the panel, etc, eventually, an optimum set up could be developed.

A solar panel uses visible light mostly, but the sun is sending IR for almost 1/2 of its energy, and UV for about the other half.

Considering that most LEDS produce little IR or UV, the beam from the LED might only have 7% or so of the sun's energy just based on wavelengths.

There's a gap in energy where the LED would need to hit the panel with enough juice to send current out the other end....and that combined with the wavelength issues makes me thing you might be able to actually just do a bezel down measurement with a conversion factor, etc.

I don't know the conversions between the light's energy and the panel's use of it though, but, it has some promise.

ISP = Integrating Solar Panel.

TEEJ said:

For example, putting the light bezel down onto the panel and turning it on should give the same thing if the surface area of the panel hit by the light is able to absorb it all.

Click to expand...

My thinking was a bigger target for long range tests, I'm OK with a lux meter for 1 metre tests.

Norm

I think, as TEEJ said, it's a matter of calibration. As a measurement device it would work, but you'd need a bunch of lights with known values to begin to plot your results.

Would the changes in voltage be linear as light increases? My guess is no. It would follow some sort of curve that you'd need to plot before any other results would be meaningful.

And I still can't shake the idea that tint would play a factor.... someone prove me wrong!

Here is one idea to see if CRI, CCT, and IR factor in much. Use an incandescent light of a known OTF/candela and a cool white LED flashlight with known OTF/candela that are almost exactly the same in measured values. If the lights have been measured with properly calibrated equipment, I think that would give a reference of how those variables may affect the voltage output of the panel.

Is a solar panel an "equal opportunity photon employer"? Or does is it discriminate on the basis of CRI, CCT, IR, UV, etc.?

Since an incandescent light is putting out a lot of IR plus the high CRI it may or may not cause a higher voltage output from the solar panel. It's an idea, anyway. I am no scientist but I think your solar panel idea is cool and has never even crossed my mind before.