LED lighting retrofit

We had a lively discussion about a year ago about retrofitting LED lighting for 48 inch fluorescents.

Well, I had the first LED fail in the last unit I made. It had flickered a couple times last week, and then went to a dim state. All the LEDs were still lit, so I thought the power supply might have failed. After checking with a meter, the voltage across the whole string was excessive. I used a DVM in diode check mode, and one LED barely lit up. I then powered it back up and measured across that LED, it was dropping 24 V! Amazing it was putting out light and not going up in flames. Anyway, I replaced the LED and all is back to normal.

These CREE LEDs have 3 solder pads on the bottom, anode, cathode and substrate, a thermal conduction path from the diodes. On this one, there was no solder wetting to the center thermal pad. Oops! I have no idea how many more might be like that. I tried to make sure the center pad was wetted, but some probably did not take.

Just thought I'd give a progress report. This unit has been in heavy use in our kitchen since April 2014. The first one of these I did has been running since January 2014.

Jon

Reply to
Jon Elson
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Jon-

I do not recall the discussion a year ago. Are there any web links for your method?

Someone in the alt.home.repair recently posted about Costco's LED Shop Lights, . I found one at the local Ace Hardware, and am impressed with it.

Rather than retrofitting existing lamps, I was thinking about replacing several with the new LED version. However it may be possible that a new lamp could be mounted on an old reflector to help distribute the light. I may try it to see.

Fred

Reply to
Fred McKenzie

LOL That "dim state" is a very tiny arc lamp under the phosphors.

Three pad power LEDs are really, really hard to solder at home. They're meant for machine assembly. I'll be very careful with the trace layout, hold my hand steady as I apply solder paste, and watch the solder flow with a magnifying lens as I heat the board. For all that care, about

20% of the LEDs need correction for having a pad that has too little or too much solder. Anything but the right amount will cause failure in 6 to 18 months.
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Reply to
Kevin McMurtrie

OK, here's a link to my page about the lights, with a picture:

formatting link

Jon

Reply to
Jon Elson

Interesting, checking the removed LED, I don't think it went bad! One of the electrical terminals, not the center one, had practically NO solder on it. Just a TINY, TINY speck. I think that solder joint went partially open. Using the DVM in diode check mode, the LED, by itself does light up quite well. On the board, it wasn't lighting due to high resistance, when I probed on the PC board. that explains why poking around on the board when powered caused it to flash sometimes.

So, I'm now pretty sure I did NOT suffer the first failure of one of the LEDs. (Just my crummy soldering!)

Jon

Reply to
Jon Elson

Watch the Costco pricing! Feit PAR38 90W 4 pack for $75 is high. I bought a bunch of Feit PAR38 90W for $12 each at Lowes.

Some of Costco prices are low but other Costco prices are not competitive at all.

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Reply to
OldeGuye

Years ago, when they first started to carry DVD titles (way before bluray), they were priced competitively against the online sellers, which means to say that $22 DVDs were sold at $17 or $18. It only took a year or so, before they were matching up with other local retailers price.

So WTF did I pay for a membership for?

On the other hand, I got a nice, HUGE extremely well made backpack for $30 that would be in the $125 class today. Built in walker, cable reinforced handles. Side handle, top handle, back pad... A *really* nice item. I wish I had bought two.

Have not given those greedy bastards any money for years though, and IF they have anything I would want, I will go as a guest of a member.

Reply to
DecadentLinuxUserNumeroUno

IKEA has LED equivalent to 60W A19 incandescents for $4.95 each. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Reply to
Jim Thompson

So very true. In addition to the defective solder joint, the entire process would cause immense eye-strain. Standard 5mm LEDs, soldered to a simple 1 layer PCB should do the task fine.

Reply to
dakupoto

No, retrofits were available then, too. But, I didn't trust them, for several reasons. If they use an off-line supply, then they need to be enclosed in an insulating tube, which will cause problems with heat removal. By making the retrofit a lot wider than a fluorescent tube (2") and totally open, I get good heat removal. Second, I wanted the highest efficiency I could get at a sane price. I start with 102 Lm/W LEDs, and with the commercial power supply, emd up with about 90 Lm/W from the wall socket. Also, putting a 120V powered lamp into something thatr looks like a

48" fluorescent tube seems like an accident waiting to happen. Somebody decides to swap a tube and POW!

I knew, going into this, it was NOT a way to save money. I can fix it myself, I'm very happy with the way it looks and performs. When I get a chance, I'm going to do some more of them.

Jon

Reply to
Jon Elson

Show me a 5mm leaded 1 WATT LED, and I might believe you. These LEDs NEED the PC board as a heat sink, and the board definitely DOES get warm! These things run at almost 3 V at 350 mA. I have no idea how much actually turns into light (a lot, actually, as your hand gets warm just getting close to the LEDs) but there is a lot of power turned into heat in the diode, too.

Well, such a device does not exist, of course, as it would burn out in a couple seconds.

Since I have a stereo zoom microscope for difficult soldering, this is not a big deal in terms of eye strain. Soldering chips with 0.4mm lead pitch is way harder! But, yes, I did make a t least one bad solder joint that eventually failed, so it is a bit hard to get it perfect.

Jon

Reply to
Jon Elson

No, EACH LED drops 2.65 - 2.85 V, the entire series string of 20 of them runs at 350 mA. 20 at 2.85 V each is about 57 V, times 350 mA is just a hair under 20 W. This string of 20 LEDs produces more light than a PAIR of 48" fluorescent tubes.

I do have a smaller unit with 10 of these LEDs in a pantry/laundry room, and it works great there, on 9 W (300 mA in that particular setup).

Jon

Reply to
Jon Elson

So you appear to be running LEDs rated for 1A ("3 W") at 350 mA, otherwise those Vf figures don't make sense. At this conditions obtaining slightly above 100 lm/W is realistic. At 20 W that would be more than 2000 lm.

Two 1200 mm fluorescent lamps will produce 5000 - 7000 lm depending on CRI. The fixture must be very bad, absorbing (instead of reflecting)

60-70 % of produced light in order to give comparable illumination levels on the floor.

The narrow light output curve of LEDs compared to fluorescent lamps

360 degrees help a lot, when no external reflectors are needed, but still I find your claim unbelievable.
Reply to
upsidedown

Well, I wanted to be conservative and give them long life. The string does get warm at 350 mA, I know it would get a lot hotter at 1 A.

I was very surprised, and I agree these things are DAMN subjective. I did use a photometer that showed the LEDs were measurably brighter than the fluorescent fixture. Now, the LEDs become essentially a line source, and the fluorescent pair are a TWO line source. So, that could have made the measurement a bit harder. So, I tried both a brightness test as well as an illumination test, measuring the brightness on the floor under the fixture. I got similar readings both ways, the LEDs were brighter. Now, this could have been a hidden spectral effect, I did not try to correct for the wavelength sensitivity of the photometer. Also, there were 32 W tubes, not

40 W, that I was comparing to.

To absorb 60 - 70% of the light, the reflector panels would have to be black!

So, I don't know why these LEDs seem brighter. Maybe my old ballasts were dying in some way, and causing the tubes to give reduced brightness. But, I'm happy with the result, the kitchen is QUITE bright. I still have one dual-fluorescent fixture that I have not gotten around to converting, so I can kind of compare them. And, the LEDs are pretty subjective, you can see a line of bright dots in the diffuser that maybe throws your eyes off. But, it is clear the LEDs are not 1/4 the light output of the fluorescents. By the way, looking up the old 40 W T12 tubes, they seem to be rated at 2000 lm. It may be the T8 tubes match the numbers you quote above.

Jon

Reply to
Jon Elson

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