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xiphmont

Oh right, about those LEDs

spoiler: Nichia Rocks. But first a flashback.

Remember those crazy Chinese LEDs I was looking for? They had kind of iffy construction, but up to that point they were the closest color match I could find to what I needed for my Thinkpad backlight project. I found more of the same type from random Chinese resellers, but none with exacly the same whitepoint as the original. I never determined the manufacturer.

I was looking for these dodgy Chinese LEDs because I couldn't get any major manufacturers or resellers to sell me the LEDs I needed in any kind of reasonable quantity. The smallest amount any factory quoted was a MOQ of 100,000 and that was only because a friend of a friend was willing to call in a favor to an unnamed factory in Hebei. The name brands you'd recognize weren't willing to discuss anything less than 1,000,000 units.

Or so I thought. I'd stopped looking slightly too early.

The AFFS LCDs I'm retrofitting have red and green filters with a lot of overlap in the yellow region because the original CCFL backlight doesn't put out much yellow. The broad yellow peak from typical white LEDs pollutes the red and green primaries. That messes up the saturation and color reproduction, even if the white point is correct.

But last year Nichia released a new line of component phosphor LEDs specifically designed for backlighting that don't use a broad yellow phosphor; they use separate red and green phosphors.

The specs also claimed tight binning, surprisingly high lumens/watt, and a weirdly low forward voltage. Oh, and they came in a low-profile 3014 package rated for mid-power output.

With no great optimism, I called up Nichia USA and asked for some samples. After being redirected a few times, I talked to a nice lady in Detroit who was happy to send me some LEDs for testing. That was farther than I expected to get.

The LED samples were everything the specs claimed them to be. I had never tested an LED as efficient, or with color binning so tight. They blew everything else out of the water.

So I called back. "What was the minimum order?" The answer: 1 reel, only 5,000 LEDs. Too good to be true.

The next question I was sure would undo me: "Can you tell me if I order now, what kind of bin I'll get?" I was still expecting to get something in the rough ballpark of what I really wanted that I could then tweak a bit with a filter. The reply: "What do you mean? You can have any bin mentioned on the spec sheet."

I could select specific whitepoint, forward voltage, and luminosity bin. At only 5,000 quantity. Jaw on floor.

It still felt too good to be true, but Nichia made the LEDs on-demand in Japan when I placed the order, and they arrived in the mail 15 calendar days later.

So as it turns out, I was able to get my dream LED for this silly little custom project. I'm reminded to post this now as there's been steady demand for the resulting Thinkpad backlight retrofit kits, and it's time to order another reel.

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Posts from This Journal by “led” Tag


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> It seems, led backlight strip in my T410 is starting to become uneven and (supposedly) fail. I am looking for replacement options (without too much hurry though) . Panel is an LG 1440x900 TN.

Actually I find this extremely interesting-- do you know what FRU that screen is? I can look it up if you don't have it handy. Native LED backlights are supposed to be carefully current-balanced to avoid that problem. I wonder if LG went a bit too far toward lowest bidder and sourced LEDs with poor quality junctions. Not all manufacturers mastered InAlGaN LEDs at the same rate. Early examples had a lot of junction instability.

I have no experience with these panels, and the appropriate replacement LEDs depends on a lot. One of the Nichias in this line could well be an appropriate replacement, but they're just as likely the wrong choice. It depends entirely on the specific panel films and color filters in the glass matrix.

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