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Old 01-30-2018, 05:10 AM   #9 (permalink)
Stubby79
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The power company sells by the watt, not by the volt-amp...So, unless they're lying as to the actual power consumption of each bulb, the stated wattage is what you will be paying.

As far as I understand it, the power difference between V-A and watts isn't lost, so presumably the power company gets it back (minus losses), and just sells it to someone else. If it doesn't get dumped in to some other part of your circuit, like some purely resistive load that doesn't care.

Now, for someone who isn't connected to the grid, I'd assume power-factor has a HUGE impact on efficiency. Which is probably why you've taken note of it.

I would assume, like most things, that the PF (Volt-amps vs actual watts, for those reading) for LEDs is mostly determined by the tiny built in power supply that converts the AC in to whatever voltage DC needed to "Drive" the LEDs. Correct me if I'm wrong, but I would assume the inefficiencies you're pointing out come from said power supply, not from the LEDs themselves. Simple power supplies (like a transformer) tend not to be very efficient. I would assume for the sake of cost-savings, that LED bulbs use cheap - not very efficient - power supplies.

If they were powered from DC from the start, you wouldn't have any of this power-factor issue. That being said, there are ways to convert A/C to DC efficiently, with a power factor of 1 (to 1)...I would think if you used one of these to power/drive all your LEDs off one such source, it would be quite efficient over-all. You could power each bulb individually, but it would probably be cost prohibitive.

The chargers for my EV use switching power supplies and have a PF of 1, or darn close. This helps maximize how much power coming out of the outlet actually gets in to my batteries. It means I can use a 15-amp circuit instead of a 20 (or more) that would be needed for a cruder charger. Also means I don't have to use oversized wires to carry the extra amps moving back and forth.

For those reading who want to understand it...If you tried running 1500w worth of these bulbs off a 15 amp, 120v household circuit...you'd blow your breaker and overload your wiring. You wouldn't be pulling the ~12a that you would with a PF of 1 (like a purely resitive load, like an incandescent bulb or an electric heater)...you could easily be pulling twice that amperage. Half of the power would go right back up the line back to the power company...but they would only charge you for the power(watts) used.

Anyway, to most people, they will never know the difference, particularly with something like a light bulb. To the occasional person who is running thing off an inverter or generator, it can really matter.

Seems the OP knows most of this.

Regarding 100 lumens per watt...you might find the LEDs themselves are actually this efficient. The 110v LED bulbs I use are rated at 7-800 lumens and supposedly consume 8 watts. It's pretty close. And, as you point out, it's the power supply that is killing the V-A. Perhaps it would be as simple as applying ~110v DC to them and you would be free of the V-A inefficiencies. And perhaps the power supplies simply wouldn't work on DC, and the only way you'd be able to do it would be to bypass their power supply and drive them directly. (sounds like a lot of work). You'd need a good, efficient switching power supply if you're starting with AC.

(You used to be able to buy CREE bulbs...as far as I'm concerned, they were the original LEDs that allowed actual bulbs to be manufactured. Other brands have since come out with similar output LEDs, so they're no logner the only option)
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