LE.....D?

[Faradave]

This came from the inside of a relatively modern TV. As I'm sure you can tell it lights up. I have a ton of them and upon closer inspection I realize that these aren't normal LEDs. When you pull off those diffusers there is just a little surface that lights up when powered. Is that that new paint? Whatever the case I accidentally gave 4 identical ones wired in parallel 20 volts. It nearly blinded me but did not blow these "lights". Well I'm doing a project with them now and I need to know if 20 volts didn't blow 4, well what's the maximum one of these can handle? Cuz I tell you they've been as bright as the Sun at one time. Oh and thats my assistant.

 

[Faradave]

Well you know what? I pulled up a manufacturer's website and it said that they can take 3 to 6 volts and 350MA (I guess they meant mA). Then again they were in parallel so doesn't that mean the current is divided? I'm not sure how many amps I was giving. Can someone go into depth here? I just need to know what's the most they can handle if I have eight of them in parallel. Or heck I could go series if you guys think I could get more brightness with less power just whatever. I appreciate it!

 

[Faradave]

Ok guys, sorry about this multiple post crap but I actually just took one of those as an experiment and gave it 20 volt all by itself. I'm seeing spots but it survived. It got brighter than I've ever seen any LED get and I kept it lit for a good 30 seconds. I need to understand what's going on here.

 

[Diver300]

It seems that they are just LEDs. LEDs are seriously bright nowadays. They are normally rated for a certain maximum current. LEDs should be supplied from a current limited supply, not a fixed voltage.

30 seconds of a significant overload won't always blow an LED. Close up, white LEDs can be seriously bright and the human eye isn't good at comparing brightnesses for small, bright dots.

I assume that strip is 8 LEDs, as you mentioned 8, although only 6 1/2 made to the picture. You mentioned the manufacturer's website but didn't put a link to it.

A strip of LEDs may have the individual LEDs in series or parallel, or a mix of series and parallel.

In series, the current is the same in each LED, but the voltage is the total of all of the voltages, so if the LEDs are in series, I would expect at least 3 V per LED, and therefore 24 V, and it wouldn't be bright on a 20 V supply. However you don't say what the 20 V supply is, and many will be more like 24 V with little load.

If the LEDs are in parallel, 8 lots of 350 mA is 2.8 A, and your power supply might not be able to provide that. A 20 V power supply that can supply 2.8 A is rated at 56 W, so it would be similar to a laptop power supply. If you had a power supply that was limited at 0.5 - 2 A, that would give 60 mA - 250 mA per LED, which would be really bright if looking directly at them.

Do you have a multimeter to measure voltage / current? Please tell us where we can see the datasheet for the LEDs or the strip of LEDs, and what power supply you are using.

 

[Faradave]

Ok, my power supply is a voltage regulator I made out of LM317, which has it's power supplied by a 33V 469mA power adapter (from which I can only get the lm317 to provide 20 volts for some reason, the datasheet says it will supply up to 31)

Unbeknownst to my family member who bought it for me, my multimeter is in fact just a dual meter. Unforch, it only measures voltage and resistance. I'm not sure what amperage the lm317 provided. That might could be determined from the datasheet.

I mentioned a manufacturers website, not necessarily the one who made these lights. I don't know that because I've separated them from the rest of their strip. I posted that one because it was unmolested and you could tell what they were originally. But have you seen those LEDs up close? There no normal LED they remind me of Electro luminescent phosphorus paint. The actual surface that lights up is just a flat square with paint on top that you can scratch off and if you do it kind of messes up the signal. Here I'll post a picture of the one I performed that experiment on. I botched it so it's all funky but you can see that underneath the top layer of paint is a sparkly layer. My finger prints for scale.

I took eight of those and wired them in parallel myself . But this is the one that survived 20 volts and didn't bat an eye . My thing is I gave that light enough juice to fry 5 LEDs at once. It got brighter then the surface of the Sun. These have got to be some kind of fancy LED.

 

[ClydeCrashKop]

Turning Smashed TVs into Realistic Artificial Daylight

 

[dr pepper]

White leds run at about 3.5v, but some chips have more than one led, probably why yours can take 20v.
The yellow is indeed phosphor, a blue led shines onto it and it converts the light to white.
Leds are now well in excess of 100 lumens / led.

 

[Faradave]

Hang on, a blue LED signs on to it? Where, from underneath? So I was right this is electroluminescent phosphor paint? My understanding of that stuff is that it's 5 layers starting with copper then something then barium titanate then the phosphor then an electrically conductive clear coat and you just add AC power to it . I was not aware of a phosphor that changes blue light to white or changes anything to anything. Can you give a link explaining this? Or possibly just explain it yourself? As if you have nothing better to do today lol just kidding I'm just curious

 

[Nigel Goodwin]

They look to be the LED's used in the 'new' cheaper LG panels, and are totally crap - with absolutely massive failure rates - it's a seriously poorly designed LCD panel, not suitable for purpose.

Basically there are too few LED's to adequately light the panel, so they are driven too hard and overheat - first failure is the picture going blue/purple as the LED's change colour under the stress, followed by the diffusers over the LED's falling off and rattling in the bottom of the panel - and without the diffusers you just get overly bright spots of light on the screen.

A friend who still does TV repairs showed me various ones he's done, and you can buy strips of the LED's from China as replacements - but it's not trivial to change them, and only available for some screens.

I was not aware of a phosphor that changes blue light to white or changes anything to anything.

Almost everything does - CRT TV's, LCD TV's, Plasma TV's, Florescent Tubes etc, etc, etc.

Phosphors are routinely used to change from one wave length to another.

 

[Faradave]

Well I have just about completely destroyed one of those and I can't seem to locate any LED what is it underneath that square? I'm pretty sure I've torn one of those off before and there was just metal but if you say so I'll tear another one off. Also I don't think I'm conveying to you how bright this led got. I might make a YouTube video or something. How many volts can I give it? Give me a bit and I'll tell you guys would it took to blow this thing

 

[Nigel Goodwin]

Well I have just about completely destroyed one of those and I can't seem to locate any LED what is it underneath that square? I'm pretty sure I've torn one of those off before and there was just metal but if you say so I'll tear another one off. Also I don't think I'm conveying to you how bright this led got. I might make a YouTube video or something. How many volts can I give it? Give me a bit and I'll tell you guys would it took to blow this thing

It's just a SM LED with a diffuser on top, and they blow regularly in normal use never mind abusing them.

 

[dr pepper]

Actually theres 2 at least white led technology's, the other is quantum dot, a ultra violet led illuminates 'quantum dots' which convert it to white.
I think a white phosphor led has a blue led behind the phosphor and the light shines though.
Early ones as you may remember appeared quite blue.

 

[Faradave]

Come to think of it it does kind of look a bit blue here at 20 volts. After this picture was taken I left it running for another 5 minutes. So that's not going to blow it. And I can't get this voltage regulator the output 30 and I don't want to just jump there I want to see it Blow slowly so LOL that will be another post later.

Okay so what type of LED are we saying it is? Do we have consensus on this?

 

[The March Muppet]

I was not aware of a phosphor that changes blue light to white or changes anything to anything.

As stated, as ubiquitous as .. well, "white" fluorescent light. The tube actually producing "white" from phosphors excited from UV mercury discharge. Something I believe due to bandgap, although truthfully I don't understand the physics involved, so I'm kind of name dropping here.

I left it running for another 5 minutes. So that's not going to blow it.

Not necessarily. LED failure mode is typically thermal. I've run insane currents through ancient T 1-3/4 indicators by grinding back the case, affixing a heat sink, and short pulse duration.

IMO, 5 minutes is not an indication of longevity operating at any particular continuous voltage and current. Conversely, you can achieve the appearance (due to persistence of vision) of increased intensity with modulation.

Not certain how different the chemistry is today, but it used to work out more of less linear: continuous current x, or 2x at 50 percent duty.

 

[Nigel Goodwin]

As stated, as ubiquitous as .. well, "white" fluorescent light. The tube actually producing "white" from phosphors excited from UV mercury discharge.

They do, and it's why the brightness of fluorescent tubes drops sharply from new, EXACTLY as Plasma TV's do - which is what causes screen burn on Plasma, and why it's only a worry while the set is still pretty new, once it's 'run in' the chance of screen burn is pretty well zero.

And I agree his 5 minute test proves nothing, although I'm pretty puzzled as to what he's trying to do? - they are SM LED's, end of story.

 

[audioguru]

I have heard that some new white LEDs use an ultra-violet LED and a phosphor. When you scratch off the phosphor then you might be blinded by the ultra-violet emission that you cannot see.

 

[gary350]

I have been looking for LED lights in a tape roll on Ebay but can not find them what is the correct name for those? I think they come in 25', 50', 100' rolls.

 

[Nigel Goodwin]

I have been looking for LED lights in a tape roll on Ebay but can not find them what is the correct name for those? I think they come in 25', 50', 100' rolls.

These aren't the same thing, they are replacement LED's for the crappy LG TV panels.

Most of the tape roll LED's are multi-colour and based on the WS2811, thus requiring a controller, which they usually come with, along with anice little remote control (or you can make your own with a PIC or Arduino).

 

[Visitor]

Most of the tape roll LED's are multi-colour and based on the WS2811, thus requiring a controller, which they usually come with, along with anice little remote control (or you can make your own with a PIC or Arduino).

Ahhhh, no. Most common are RGB LEDs and single color LEDs.

 

[Faradave]

Oh hey guys. Well, I wasn't testing longevity, in my experience when an LED burns out it happens quick, it suddenly gets real bright then the little prongs turn orange and then it's dead. That's the kind of blowout I meant. And yeah that's not a tape, I pulled those out of broken TVs. Since you asked what I was using them for I'll show you but warning, it's rated R

Inappropriate images deleted by Moderator.


I know, you can see the light source too well. If I had left the diffusers on, not enough light gets into the plexiglass. It's my first time doing something like this. After I start it I realized I should have put red LEDs in the bottom and blue LEDs in the top.