meaning of "3W" LED rating - Page 1
Forum section: electronics / projects

author: JBeale
author_rank: Frequent Contributor
timestamp: November 28, 2016, 09:19:42 pm
content: Sorry for what is probably a silly question. If I look for a 850nm 3W LED on Ebay, I find a lot of hits, and most of them list current and forward voltage but the product is not anything like 3 watts. For examplehttp://www.ebay.com/itm/261910880884which includes VF and IF as follows:DC Forward Voltage (VF): 1.8-2.2VDC Forward Current (IF): 700mATo me, this means the LED uses between (1.8 * 0.7) = 1.26 W and (2.2 * 0.7) = 1.54 W which is a lot less than 3W so what am I missing? Is 3W an instantaneous peak power limit, or does "3W" somehow mean a particular style of LED design, rather than a power rating? Or does it mean nothing and I should not expect a component spec on ebay to make any sense?

author: Monkeh
author_rank: Super Contributor
timestamp: November 28, 2016, 09:26:14 pm
content: Simple, it means they're liars.If you want a real 3W IR LED it's going to cost more than 99 cents. China can't be trusted to supply the real thing.E: Here's a real ~3W LED:http://www.digikey.com/product-detail/en/bridgelux/BXIR-85090BA-1300/976-1491-1-ND/6150824

author: RoGeorge
author_rank: Super Contributor
timestamp: November 28, 2016, 09:29:49 pm
content: Only the the datasheet from the LED manufacturer can answer your question. I never trust the seller specs unless they are backed up by the manufacturer specs.

author: Fungus
author_rank: Super Contributor
timestamp: November 28, 2016, 09:43:58 pm
content: Quote from: JBeale on November 28, 2016, 09:19:42 pmThat just means they're resellers, not engineers. They probably copy/paste the text from several different articles.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2016, 09:46:19 pm
content: "3W", as in, the package will do that, maybe, before it poofs.White LEDs in that size are normally sold as "3W", but they're really 1W (~300mA) if you want any lifetime out of 'em.IR of course will do a bit more current, for the same power. But mind that the current limit is die limited, too: at very high current (high injection regime), (quantum) efficiency tanks, and also, ESR dominates (excess Vf drop, heat).Tim

author: madires
author_rank: Super Contributor
timestamp: November 28, 2016, 10:35:05 pm
content: 2-3 Chinese Watts are about 1 WattI'm sorry to say this, but this conversion works dismayingly well.

author: sleemanj
author_rank: Super Contributor
timestamp: November 28, 2016, 11:15:49 pm
content: The 3W "star" type leds, yeah, not 3W consumption, even in white it would only be 2.2WThe 1W versions are close to 1W consumption.As to why they call them 3W instead of 2W like would be more reasonable... could be various reasons, ranging from being misinformed, to maybe the light output is 3x more than the 1w versions even though power consumption is 2x more (not saying it is, just one possibility).But in any case, measuring LEDs by power consumption is not so incredibly useful anyway, it's not really directly correlated to light output, especially between different types of leds (let alone different wavelength)

author: Fungus
author_rank: Super Contributor
timestamp: November 29, 2016, 12:36:52 pm
content: Quote from: madires on November 28, 2016, 10:35:05 pmFor anything above "1W" on eBay I generally use a factor of 2 for conversion to real Watts.