Low cost bulk LED from China almost worthless!

[BlackICE]

I got a 50 discrete 5mm white LED from ebay for only $1. They seemed to work fine for intermittent use. However I used some for 24/7 lighting and they soon dim to less 1/10 brightness less than 6 months. I tested my circuit, the bridge rectifier and filter cap checked out, the voltage drop and current draw for all the LED were fine, just the light output was very dim.

I guess I will have to get quality LEDs from known suppliers and not from ebay or Amazon where you never know what you get. The money saved doesn't overcome my labor to rebuild the circuit.

[amyk]

Are they taking on a blue hue? It could be phosphor degradation.

[retiredfeline]

How much current are you running them at? They are meant for indicator use and not general lighting.

[BlackICE]

Yes they were taking on the blue tint. I was running 4.7 milliamps through them. They didn't have any specifications and I thought that would be a safe limit. I've read that normal LEDs have a lifespan anymore from 10000 to 50000 hours or more. These fell way short of that.

[I wanted a rude username]

I guess I will have to get quality LEDs from known suppliers and not from ebay or Amazon where you never know what you get. The money saved doesn't overcome my labor to rebuild the circuit.

Yes, and it's a valuable lesson that we all learn ... better sooner rather than later.

There are some excellent LEDs in newer packages such as 3528/2835 which are far more efficient due to their much larger chips, so you can derate them (higher value resistor) and get pretty much unlimited lifespan (as long as you don't expose them to sunlight), and you can pick your preferred colour temperature and forward voltage instead of "luck of the draw". A good budget example is the Honglitronic HL-AM-2835H421W series.

[wizard69]

Did the LEDs come with a data sheet?   That should be your first check box when looking for quality hardware.   If a vendor can’t supply the manufactures data sheet, there is a high likelihood that trash is coming your way.   This doesn’t stop manufactures / suppliers that are total frauds but it is a filter. 

Beyond that price is and always has been an indicator of quality (at the extremes).   Do you really believe that that many LEDs for the price you imply is reasonable?    I really don’t think it is the case even for stuff from quality manufactures in China. 

[Jwillis]

Ebay can be tricky to get quality but it can be done . 
First:  If the deal looks to good to be true it probably is .
Second: Check what else they are selling . If they sell fashion accessories and LEDs you probably want to go some where else. If all they sell are electronic components and other electronic related products then you'll probably be OK.
Third : Always check the responses from other buyers and how the seller describes the components. If things look really off , then you probably want to avoid it.

[james_s]

If you paid $1 for 50 of them it should not be surprising that they are of low quality and do not last. Look up what a reasonable LED from someplace like Lite-On, Kingbright or other reputable manufacture costs. If you're getting something for a fraction of what a reputable product costs in moderately large quantities then you're probably not getting quality.

[amyk]

as long as you don't expose them to sunlight

Good point. The phosphor can also be degraded rapidly by UV.

[jmelson]

I've been running Cree XPEBWT lighting LEDs in our kitchen for about 10 hours/day for the the last 6 years with minimal loss of brightness.  They are running at 350 mA, but with a copper PC board as a heat sink.
So, good LEDs can last a long time.

Jon

[floobydust]

It's hit or miss off eBay or Ali, some LED's are excellent, others are oddball colour. china doesn't waste anything, the LED's could be rejects. I've noticed the polarity markings are usually backwards. So either they packaged them wrong or this is a way to use up the junk and sell it.

[strawberry]

[wizard69]

as long as you don't expose them to sunlight

Good point. The phosphor can also be degraded rapidly by UV.

OK this doesn't really make sense to me.   The white light LED's, as I understand them, use UV light to excite the phosphor.    I'm not sure how the low level exposure you would get outdoors would impact the  phosphor.

[tooki]

White LEDs almost universally use a blue LED with yellow phosphors. (Cheap ones using monochromatic yellow, better ones using “wideband” phosphors covering most of the visible spectrum.)

[I wanted a rude username]

OK this doesn't really make sense to me.   The white light LED's, as I understand them, use UV light to excite the phosphor.    I'm not sure how the low level exposure you would get outdoors would impact the  phosphor.

Direct sunlight is about 1 mW/mm², so about 7 mW across the surface of a 3528 LED's 2.9 x 2.4 mm phosphor area. Much of this power is at lower frequencies including infra-red, but a significant portion is at more damaging UV frequencies which the phosphor is not designed for.

In contrast, that LED's output can be quite useful (indoors) at 100 uA, or about 300 uW. So being outdoors exposes it to an order of magnitude more radiation overall ... and many orders of maginitude more UV.

[james_s]

Sunlight certainly does cause a lot of materials to rapidly degrade. It would be interesting to do some scientific tests here, put some LEDs out in the sun for various lengths of time and keep a control sample stored away.

[BlackICE]

The LEDs were mounted facing down with an overhang covering them. They had no direct view of sunlight. Although sunlight reflecting off the pavement would hit the LEDs from the ground.

[BrokenYugo]

I would think the 2+mm of whatever plastic clear body 5mm LEDs are made from would stop most UV from reaching the phosphor?

In any event, when no specs are given on chinesium parts one must assume the worst, in this case OP wasn't quite pessimistic enough.

[james_s]

In this particular case it's obvious that the LEDs are just cheap crap, I mean they were a dollar for 50, they're going to be garbage.

[BlackICE]

I replaced the LEDs from the bulk buy with some I included in an low cost electronics parts kit hoping they would perform better. However in less than 2 months I think I already see some degradation in the light output. I doubt that the 5ma I'm putting through a T-1 3/4 5mm LED is overheating them when the spec for most in this size are >=20ma and many to 30ma.

I'm ready to order quality parts from Digikey, but am amazed that none of the datasheets show light output vs time in service. I found this on the web from someone seeing the same problem.


http://www.nickhill.co.uk/white_LED_life_expectancy.html

More supporting evidence of pool lifespan of typical 5mm leds.

https://cool.culturalheritage.org/byorg/us-doe/lifetime_white_leds_aug16_r1.pdf

How long should I expect a white T-1 3/4 LED to last at 5ma under continuous service before the light output falls to 50%?

[Kim Christensen]

I tested my circuit, the bridge rectifier and filter cap checked out, the voltage drop and current draw for all the LED were fine, just the light output was very dim.

Can you post a schematic of the circuit?

[BlackICE]

12vac from transformer into a 4 pin dip bridge rectifier with a 35v 470uf cap across it yields a filtered 16.9VDC. The DC is fed to 4 LEDs in series this is in series with a 1K resistor. I measured the current to be about 5ma.

[johnboxall]

All these people who buy cheap sh!t off ebay or aliexpress remind me of the episode of the Simpsons where Homer buys cheap ham from the Kwikimart. The ham was off and makes him sick so Homer goes back to complain, and Apu gives him two buckets of prawns as compensation - which Homer then proceeds to eat and be sick again.

[BlackICE]

All these people who buy cheap sh!t off ebay or aliexpress remind me of the episode of the Simpsons where Homer buys cheap ham from the Kwikimart. The ham was off and makes him sick so Homer goes back to complain, and Apu gives him two buckets of prawns as compensation - which Homer then proceeds to eat and be sick again.

That sums it up pretty well. However I'm not convinced buying better ones will last as long as I would like them to >50K hours.

[xavier60]

FWIW, my experience with cheap gull-wing power LEDs from China has been good so far.
https://www.eevblog.com/forum/projects/cheap-1w-3w-leds/msg3885341/#msg3885341