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Old 12-22-2015, 01:10 PM   #41
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Thanks for the explanation, and the info about the phosphor UV-->visible light coating (like florescent bulbs have). If they do stop glowing very quickly, I'd imagine it would be apparent in regular fast shutter speed photographs of the bulbs (1/500 second). Sometimes every other bulb would be lit, sometimes none, etc.
Under the category of 'geeky fun', I managed to verify this w/o any equipment at all.

I took a loose LED string I had, and in a darkened room, held the last LED in the string in my hand, and whipped it back and forth quickly in an arc ( ~ 9 inches wide?). It was easy to see a streak of light, broken by the off times. Like a dashed line, maybe 3-4 on cycles shown. A little hard to make out, but it did look like the off time was longer than the on time, as expected (off for half the cycle, plus the time it takes to reach the threshold of LED turn on).

I then took an LED from the beginning, held them together and repeated it. I expected to see the on/off periods alternate. But they didn't!

More experimenting with a diode at the plug side, and it turned out that they didn't bother to alternate the polarity of the two 25 LED halves (the diode would turn the entire string on/off, rather than a half string at a time). At these low power levels, it doesn't really make any significant difference in terms of power balance. I just figured they'd be set up that way as part of the production process.

DW was not impressed.

On these strings I've bought the past few years (the Walgreens warm-white), I dont see any resistor in the line. Some others I had had a little module. I tested an individual LED, and it does not seem to have a built in resistor (I can't be certain, but the 170 V peak / 25 is 6.8 V and these things get very bright by ~ 3.7 V, and drew ~ 64mA. That's ~ 1/4W and I'd be afraid of blowing them with any more). Can't find any resistor though. Yes, I'l do some measuring from plugs to socket... later.

-ERD50
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Old 01-10-2016, 12:40 PM   #42
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I was in Home Depot the other day and saw two types of LED replacement "bulbs" for the ubiquitous 48" T8 florescent bulb. One type was a direct replacement (so the power continues to go through the ballast in the fixture) and the other type required slight re-wiring of the fixtures so that the bulb gets straight 110VAC. The second type is about twice as expensive, but has the advantages of higher efficiency (lumens/watt) and higher reliability/longevity in use (no possible failure of the ballast.

I imagine that the second type is just a bunch of LEDs wired pretty much like one of these Christmas light strings, so that there are enough LEDs wired in series so that each bulb gets enough voltage to stay within its max limits.

Question: If these LEDs are actually drawing power only during about 1/2 of the total sine wave, is the electric meter going to bill me for the whole thing, or just for the portion used?

I have an old, useless florescent shop light (bad ballast that would cost more than a replacement fixture). I'm thinking of making a homebrew LED shoplight using a few strings of LED Christmas lights purchased on sale--just drill a bunch of holes in the reflector and put all the wires inside the housing that used to hold the ballast, wires, etc. Not UL approved. It's probably no cheaper than just getting an old-fashioned drop light with clamp and reflector and putting in a 10W LED bulb with an Edison base (the typical "60W replacement" bulb). Fun, fun!
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Old 01-10-2016, 01:02 PM   #43
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Wow! There are lots of those T8 replacements now. I've been watching them for several years because I have some soffit lights that need new ballasts, but now the LED bulbs are cheaper than new ballasts and put out more light. I hate replacing ballasts because I have yet to do it with out slicing a finger on the cheesy metal housings. I may just decide to slice my fingers up putting in LEDs instead.

Last time I looked, the T8 replacements were ~$100.
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Old 01-10-2016, 01:17 PM   #44
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Last time I looked, the T8 replacements were ~$100.
Yep, they are quite a bit less now. IIRC, the "direct replacements" (no re-wiring to eliminate the ballast) are about $14 each, and the ones that require/allow elimination of the ballast cost about $30 each. Neither is significantly more efficient (lumens per watt) than the T8 florescent bulbs, and the LED units often put out fewer lumens than the T8 florescent bulbs, so the payback period would be very long. The reasons to change would be convenience (fewer bulb changes), reliability (esp if the ballast is eliminated) and near-instant full brightness regardless of temperature.
There's no "native" LED replacement lamp standard yet--they are now just emulating the legacy Edison-based incandescents and the 48" T12/T8 florescents. Maybe there will never be a new replaceable LED lamp that is unique to that technology--the old formats are well entrenched.
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Old 01-10-2016, 02:13 PM   #45
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...
I imagine that the second type is just a bunch of LEDs wired pretty much like one of these Christmas light strings, so that there are enough LEDs wired in series so that each bulb gets enough voltage to stay within its max limits. ...
I doubt it. The flicker would be pretty bad, and noticeable as you move under the light. Since people don't really work under the Christmas lights, and they are low brightness, the flicker isn't such a big deal. I'm pretty sure any indoor work light will have a switching supply built into it that switches at a high frequency.
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Question: If these LEDs are actually drawing power only during about 1/2 of the total sine wave, is the electric meter going to bill me for the whole thing, or just for the portion used? ...
The watt meter averages out the draw. Watt meters don't account for power factor (which you could read with a Kill-a-Watt meter if you can plug it in), you are only charged for watts.

-ERD50
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Old 01-15-2016, 01:30 PM   #46
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In conclusion I've decided to install the incandescent C9 bulbs and I wasn't impressed with what Lowes, Home Depot, Rona sold. Maybe I'll check back online during boxing day or what you Americano's call "Black Friday". When is that by the way?
It's Thanksgiving's Day's Boxing Day!

Mike D.
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