High Power LEDs on eBay - Page 1
Forum section: electronics / general

author: hpmaxim
author_rank: Regular Contributor
timestamp: March 30, 2020, 06:57:11 am
content: I was looking for high power LEDs on eBay and found this:eBay auction: #371762434003It's worth noting that I'm calling this out as typical. I saw many other LEDs on eBay that had similar specs, and I'm trying to understand it.They claim this is a 30W LED, but it has a forward voltage of between 12 and 15V and a forward current of 1A. Last I checked Wattage is ALWAYS equal to or less than volts * amps, so shouldn't this be a 15W LED? I understand that you should take the specs of a product you buy from China with a grain of salt, but their own specs are saying they are lying about their own specs. It gets worse too... they then claim radiant power is between 2 and 2.3W. So that means a "30W LED" is producing 2.3W of light and 12.5W of heat? That's 15% efficient? I'd have thought LED efficiency, particularly in infrared (which this is) would be in the 30-50% range.Am I missing something here?

author: Siwastaja
author_rank: Super Contributor
timestamp: April 02, 2020, 09:48:33 am
content: Ebay LEDs are completely random, some are actually very good, some are rejects, either non-working or failed the lowest intensity bin, so really inefficient.Their specifications are, in any case, completely random numbers. If you really need 940nm and not 850nm, you have already a risk there, how do you know it's really 940nm? You need to do your own guesswork; look at the typical power ratings of proper LEDs with similar die sizes and package sizes. Derating the power further helps.I simply stopped buying the Ebay LEDs years ago because luck is a too big of an element. If you have around 20-30% chances of getting what you want, you need to rebuy about 1-5 times depending on how lucky you are, costing you months of time.A proper high-quality IR LED can indeed be in the 30-50% efficiency range as you say, but note the catch that even if you buy the brand name OSRAM LED or similar, and the front page screams 40% efficiency, the actual intensity bins that satisfy this efficiency may be very expensive, or unobtanium, even vaporware. Calculate the efficiency for the intensity bin you are actually buying.For a 30W design, bying the proper OSRAM, Liteon or similar IR emitters from Digikey and designing an aluminium-core PCB for them will not be that much more expensive, and you get the pattern you need.

author: hpmaxim
author_rank: Regular Contributor
timestamp: April 09, 2020, 03:04:52 pm
content: I hadn't even thought that these were binning rejects, and it doesn't surprise me at all that its a crapshoot or that they wouldn't meet the specs they publish, but...1) Something like current and voltage are trivially tested, I'm just surprised that they wouldn't get called out on it by the buyer and get a claim filed against them if the forward voltage is wrong or if the part blows up when you put the rated current through it.2) It's hard for me to understand how you can claim an LED is 30W and simultaneously claim forward current is 1A and forward voltage is 15V. I mean, is there any math or rating system where 1A and 15V works out to 15W? I just don't understand how they can have any customers when they so brazenly claim specs that contradict themselves. Or is that the plan? Like the Nigerian scammers, they create a listing so stupid that only idiots would buy it and they are less likely to complain when it doesn't meet spec, and if they do complain its not 30W, then the defense is, we said its 1A at 15V....