In the dark, the photocell’s resistance is high, and the voltage divider’s output is sufficient to charge the capacitor C2 quickly, achieve breakover voltage of the diac, turn the triac on, and bring the lamp to full brightness.
It is my understanding that flourescent lights are life limited by two things: hours of use and number of starts. For that reason automatic light sensors should have a longer "hang time", leaving the lamps on for as much as 30 minutes once they are lit. Incadescent lamps are much less sensitive to starts (although they, too, typically fail at start) and so can be set for much shorter hang times to save on the electricity.
I'm a bit of a lamp snob; I'll only buy from the "big 3," GE, Philips and Sylvania for quality reasons. I too have been installing CFLs in my house since they firsat started becoming available and my utility offered rebates (no longer available) to try to make them economically viable. I haven't been able to put them yet in any fixture served by a dimmer switch and I discovered a long time ago that they fail quickly if they are switched on and off a lot so I don't have them in my walk-in closet. In my vanity light bars, I mix CFLs 50-50 with incandescents because of the warmup time. I have a 42W spiral CFL burning base up in my laundry room and my family complains about the time required to come to full lumens. Dick doesn't say how well insulated his garage is or where he lives but my garage might be too cold for 1/4 - 1/2 of the year for the CFLs (or the linears that somebody else mentioned) to come up to full lumens quickly.
Makes me think of another idea. Maybe its already out there and I haven't noticed, but why not use gradual dimming and brightning for car headlights. Seem like a concept that would be a very welcome chance to the sudden flash seen when switching between high/low beam.
No doubt there are other solutions. The floods are a good choice for aiming light where it is needed. For example, two are pointed towards the garage door area to illuminate that area of the garage, even though the lamps themselves are some distance from the door in order to be clear of the door when it is raised. Although I could have installed low-profile tubes directly over that area, they would have been covered by the raised overhead garage door, and I would have had a potential dark spot.
From your responses to comments, Dick, it sounds like the light you created was the ideal solution to your lighting needs -- given what was available. Thus, it makes for a great gadget, one that meets specific needs in ways that no other solution on the market can.
"TL" fluorescent tubes are typically mounted on a carrier but those can be very low profile and you can feed the wires from any side. I have here a TL variant that is less than 1" total height (carrier with build-in electronic starter + tube).
The entire assembly (carrier + tube) clicks into two small brackets that you screw to the mounting surface and there is a plug on either side of the carrier to power it.
I don't see how this would be worse than the plastic rails for wire distribution to boxes with screw fittings for floodlights.
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