LEDs as Photo-diodes

But surely you knew this already?

It all depends on the phosphors used, many are sold with “afterglow” to varying degrees, and would actually smooth out the zero crossings of the AC, but the discharge itself stops for a significant part of the cycle, being reignited from the heaters.

I was surprised that it seams to go to zero.

My now deceased neighbor used to make remark when ever given the chance that when florescent lights were introduce to machine shops injuries happened because people were fooled about the machine’s motion. He says that the early generations lights were bad for that. That had me thinking the effect was reduced. To see the ADC measured value go to zero was a surprise.

But I know that when I watch the teeth on my table saw blade spin down it strobes backwards and forward. Hum. I should put a sharpie mark or three on my blades come to think of it.

I also see a distortion at the positive peaks that I also did not expect.

Again, no surprises there.

It is a gas discharge tube. It is by no means whatsoever a linear device.

Now what about your tests on an LCD LED luminaire? Note that “white” LCDs LEDs are indeed by definition, fluorescent lights! :grin:

Paul,
Regarding no surprise. Please elaborate.
If you look at the read me file at my github for the LEDasSensor

On the graph of " Ripple and Interference on LED" you will see a wiggle at the postitve peak for which their is no corresponding wiggle at the negative peak.
In other words I see one “complete” turn off in every 16mS (=1/60). I might have expected to see two since I would assume both the positive and the the negative swing side of the AC waveform would be making light. HUM… Maybe their are. There would be two zero crossings which would be where the light stops. Hmmmmm. But the zero crossings would come ever 8mS not 16mS.

With out fear of contraction I can say I do not understand why I am seeing what I I am seeing on the LED waveform.

Not sure what you mean an LCD light? I have ancient late 1980s “standard” mercury vapor florescent tube lights in my lab. I also have an LED flash light for a “DC” light source.

I believe, both are almost same and you can do as there are many tutorials, but the issue is that that both of them have the different orientation of the transistor

Again, I am not really surprised. This certainly does suggest that the fluorescent tubes are not operating symmetrically but - that is perfectly plausible! I mentioned that the initiation of the discharge (on each cycle) is dependent on the tube heaters and there are two heaters in each tube and these tend to degrade over time, so there is no guarantee this happens symmetrically.

And I presume you have multiple tube fittings and more than one, so you will be seeing a composite of those. Have you tried moving your sensor around the room to see the behaviour of different luminaires?

Oops! Typo! :woozy_face:

Interesting idea on moving the sensor around. It is on a short tethered to the PC for now. Perhaps the future.
Thanks,

I need to find an incandescent lamp to try too. Getting harder and harder…