Cheap chinese RGB LEDs

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Rezer
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Posted by Rezer: Thu. Feb 9, 2017 - 05:59 AM
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I picked up some dirt cheap PLCC-6 RGB LEDs from ebay a while back, the usual sort you get from ebay with no datasheet or manufacturer to speak of.  I started playing with some of them in a small LED matrix for a project, and the first thing I wanted to do was figure out how to mix the colors to get something close to white.  I quickly found out that the red was severely unbalanced with the green and blue, to the point where I have to give it around 10 times more current to get decent color mixing, and it's not just a single shoddy LED...the whole batch was like that.

 

I broke out a light meter I happened to have lying around, and the balance in luminous intensity when driving all 3 colors at the same intensity is, in order RGB, 1 to 11 to 14.  I know it's not just my shoddy light meter either, cause when I adjust the current based on a theoretical 3:6:1 luminous intensity ratio to get white it's actually white, but that requires driving red with 20 mA, green with 3.2 mA, and blue with around .4mA.

 

Now, obviously, buying cheap LEDs on ebay is less than optimal, sure.  I'm just curious if anybody else has had similar experiences with these things?  I expected them to have uneven brightness and not last a terribly long time, but I wasn't expecting such ridiculously unbalanced intensity.

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Learning and Information, General Electronics
Last Edited: Thu. Feb 9, 2017 - 06:06 AM
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awneil
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Posted by awneil: Thu. Feb 9, 2017 - 07:52 AM
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Well, without a datasheet you have no foundation for any expectations at all!

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Rezer
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Posted by Rezer: Thu. Feb 9, 2017 - 08:40 AM (Reply to #2)
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Granted, but they're operating pretty far outside of what one would consider "typical" for these things.  I've been looking through datasheets for similar LEDs and they range from around 3:6:1 intensity at equal current best case to 1:4:1 worst case.  I guess when they're this shitty the manufacturer doesn't even bother putting the specs down on paper, so there's nothing floating around on the internet with a comparable datasheet.

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donotdespisethesnake
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Posted by donotdespisethesnake: Thu. Feb 9, 2017 - 09:28 AM
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I'll bet a lot of stuff on ebay is batches rejected due to quality problems. Rather than than toss them in a dumpster, they sell them off as seconds to whoever will pay for them. In the worst case, they end up back in "grey market" supply chains. That's assuming they are legit of course, there is also a huge amount of counterfeit or cheap copies remarked.

 

 

Bob. Engineer and trainee Rocket Scientist.

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awneil
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Posted by awneil: Thu. Feb 9, 2017 - 10:03 AM (Reply to #4)
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donotdespisethesnake wrote:
Rather than than toss them in a dumpster, they sell them off as seconds

Or, "floor sweepings"

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JoniS
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Posted by JoniS: Thu. Feb 9, 2017 - 10:05 AM
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donotdespisethesnake wrote:
That's assuming they are legit of course, there is also a huge amount of counterfeit or cheap copies remarked.

And this is pretty much why no one should ever expect anything from stuff they get from eBay. 

 

I wasn't too surprised if some of the sellers didn't even know they sell fake products etc.

 

E: pretty good example is addressable led strip I got yesterday, first led was not working at all which led me to think that whole strip is not working initially, and somewhere on the later part of the strip is one which does not work either(can't control leds after that). Also I can spot little differences on the Led brightness all over the place, well it was cheap.

Last Edited: Thu. Feb 9, 2017 - 10:24 AM
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awneil
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Posted by awneil: Thu. Feb 9, 2017 - 10:10 AM (Reply to #3)
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Rezer wrote:
they're operating pretty far outside of what one would consider "typical" for these things.

But, again, there is no foundation for the assumption that they should be in any way "typical" of anything.

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Brian Fairchild
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Posted by Brian Fairchild: Thu. Feb 9, 2017 - 10:20 AM
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Rezer wrote:

...but I wasn't expecting such ridiculously unbalanced intensity.

 

How flat is the spectral sensitivity of the human eye?

How matched are the wavelengths of the LEDs to the wavelengths of the cones in the human eye?

How flat is the spectral response of your light meter?

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John_A_Brown
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Posted by John_A_Brown: Thu. Feb 9, 2017 - 10:45 AM
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Let's face it, if you wanted to buy made in the USA LEDs, you'd probably have to pay a whole lot more.

I daren't say any more for fear of breaking the rules/waking up Bob.

 

Four legs good, two legs bad, three legs stable.

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Rezer
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Posted by Rezer: Thu. Feb 9, 2017 - 10:50 PM
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Brian Fairchild wrote:

How flat is the spectral sensitivity of the human eye?

 

Not at all, but when LEDs are speced by luminous intensity the scale's already pinned to human perception.

 

Brian Fairchild wrote:

How matched are the wavelengths of the LEDs to the wavelengths of the cones in the human eye?

 

My initial assumption was that the red was "too deep," which leads to vastly reduced perceived intensity.  However, when I compare to other red LEDs the color seems to be about right.

 

Brian Fairchild wrote:

How flat is the spectral response of your light meter?

 

I have no idea, which is why I calculated the theoretical white point value based on the readings to verify it was at least in the ballpark.  It's likely over-reporting the blue intensity to a degree since the white color looks to be lower temperature than it should be, increasing the blue current by about 50% fixes this right up and it's a nice daylight color.  That still leaves blue at around 10 times the intensity of red at the same current, which I find very odd given what I (think I) know about LEDs.

 

Nobody so far seems terribly shocked that cheap crap from china is cheap crap, but I just couldn't find any mention of this kind of behavior anywhere when I asked my buddy google, so I figured I'd run it by you guys to see if I'm taking crazy pills...seems the consensus is I just needed to lower my expectations a little more.  Oh well, they work fine for my purposes, just can't squeeze out as much brightness as I could with properly balanced LEDs if I want certain colors.  But hey, they were $0.05 each!

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awneil
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Posted by awneil: Thu. Feb 9, 2017 - 11:59 PM (Reply to #10)
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Rezer wrote:
Nobody so far seems terribly shocked that cheap crap from china is cheap crap

Why would that come as any kind of shock or surprise at all?

 

I very much doubt that the country of origin is of any significance:  cheap crap from anywhere is cheap crap

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillator: https://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
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DocJC
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Posted by DocJC: Fri. Feb 10, 2017 - 12:28 AM
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Wow, I thought I splurged when I bought a 50 pack of RGB leds from BangGood Electronics for $3.63, (That's 7 cents / LED).

(You mentioned you paid 5 cents each)

I added it to another order just to toss some in the parts bin, for general tinkering, when a specific spec'd part doesn't matter.

 

At least the extra 2 cents each gets one some spec's:

 

Current : 3V

Voltage: 20 mA

Size: 5mm 

Light Color: RED, BLUE, GREEN

Total Quantity: 50pcs

 

Package included:
  

50 x Cathode 4-PINS F5 5mm  LED Light

 

 

OK, so the spec's are pretty meaningless...

(Is that a Max current, listed as a voltage?  Vf info? etc)

 

Maybe I should have purchased from your junk dealer instead and saved a buck!

 

JC

Last Edited: Fri. Feb 10, 2017 - 12:31 AM
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Rezer
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Posted by Rezer: Fri. Feb 10, 2017 - 01:09 AM
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awneil wrote:

Rezer wrote:
Nobody so far seems terribly shocked that cheap crap from china is cheap crap

Why would that come as any kind of shock or surprise at all?

 

I very much doubt that the country of origin is of any significance:  cheap crap from anywhere is cheap crap

 

I may have meant that comment with a touch of sarcasm. wink  And your statement is definitely true, but china does a fair job of flooding the market.  My goal isn't to disparage the country of manufacture here, that's just where trade imbalance dictates I get my cheap crap from!

 

And DocJC:  Did you ever do anything with them?  Wondering if the $0.02 got you more than those mysterious looking specs, I'd be willing to fork over the extra pennies for something marginally more balanced.

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DocJC
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Posted by DocJC: Fri. Feb 10, 2017 - 03:21 AM
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Sorry, they are just sitting in the parts bin.

I intend to measure their forward voltage and see how they perform on 2, 5, 10, 20 ? mA.

I don't have a light meter, so I'd have to build one to measure their energy output, (and that, unfortunately, is getting added to the project list, but its at the bottom...).

 

JC 

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