Hi,
What kind of power in the LED's are you working with. Do you have a lot of high power LED's or just a few small ones or what? I ask because you might be able to build your own controller that is simply a PWM circuit.
The control scheme for this would be a little tricky. There are several issues. I'll name a few...
1. The light from the LED's cant affect the sensors too much or they will just keep getting brighter and brighter.
2. Probably need more than one sensor, pointing in various directions.
3. The sensors positions and directions and the lighting sources in the room will affect the control law, so lighting sources probably have to be fixed in position and if directional their direction fixed also.
4. You'd have to establish a min and max threshold for the ambient lighting, then work from there. The controller would have to be adjustable so you can adjust what the min and max are.
So a typical scenario might go like this...
You install one or more sensors in a fixed location that you believe will sense the ambient light that will be representative of the usual room lighting. You then measure the resistances of all the sensors at the min and max ambient light that is to be expected. You then drive the LED's with a PWM signal that is adjustable, and decide on the min and max LED current level you need for the min and max ambient lighting. You then use the min and max resistance in a PWM circuit that will adjust the current to the LED's, and hope that any non linearity is not noticed too much. If it is noticed too much you'd have to create a non linear slope for the control signal.
So there would be a couple steps to getting this right, which include a test set to be performed with results carefully logged.
You'd also want to think about how the system should react to people standing between the main lighting source in the room and the sensors, or the windows and the sensors during a bright day.
So there is a little bit to it im afraid. Success might be hard to measure with all the variables that can come into play.
Thank you for the thorough reply. To answer your questions, I have only 2 high power LEDs. They are Editar 100 Watt / 7000 Lumen LEDs. I believe their primary use is in street lights. Each LED chip is mounted in a lens with integrated heatsink. I already have a very nice driver (one for each LED). Both the LED enclosure and driver are IP65/67 rated for wet locations - a good thing because they are splashed with saltwater 24 hours a day (for the last 6 months).
A: 1. The light is focused downward, and there is roughly 10 feet of open space above to place the photocells.
A: 2. I completely agree
A: 3. The ambient lighting comes from 4 skylights, and intensity varies with time of day, time of year, and weather conditions. It would be possible to mount photocells within each skylight, or at several points within a skylight to improve the precision. The skylights are roughly 10 feet above the LEDs.
A: 4. I would like to provide the finished and tested schematic to my peers so they might benefit as well. To that end, it would be nice to have a wide range of adjustment because their setups will be quite a bit different.
I would not want to replace the existing drivers, but they are quite flexible, and I'm hopeful we can come up with something to control them.
The drivers will accept 3 types of dimming signal:
1. Resistance - 10KOhms = 10% output .... 100KOhms = 100% output .. Open = 102% output -- this is how they are currently running
2. Voltage - 1V = 10% output ... 10V = 100% output
3. PWM = 10% = 10% output ... 100% = 100% output
The full driver specs, including dimmer requirements, are attached to my first post as a PDF.
Would it be possible to put a bunch of LDR's in parallel with a Pot or two for adjustment? Do LDRs exist where resistance goes up with light intensity? The ones I see all go down with more light, and that's the opposite of what I need.