Yes, Virginia, LED's Do Get Hot

[jim6918]

If you were ever under the assumption that LED’s do not create heat like incandescents, I am here to tell you that you are so wrong it could be dangerous. I have always noticed how cool LED strings operate, so much so in fact that I often have to bring them into a warm place just to get them flexible enough to unwind new sets. Apparently LED rope lights create a hell of a lot of heat.

This past Sunday, I cracked open a roll of LED warm white rope light just to check out the color. I did not unwind the lights from the 150 foot roll. Again not thinking of any heat issues I left the roll plugged in while I puttered around the garage. I went in to eat a quick dinner and when I came out I smelled burning rubber. I tracked it to the LED roll and noticed that the plastic roll was starting to soften. Well, to make a long and darn expensive story short, the roll of lights was nearly at a flash point, and I am pretty sure that I caught it only minutes before the whole things would have burst into flames inside a closed attached garage with two vehicles.

I have always taken extra care with my Christmas display, making sure that there are no electrical issues that could cause a fire, and here I nearly burned down my house just by something so stupid. You can never be too careful.

Well, it all adds up to a very expensive lesson; at least all I have to replace is a $225 roll of LED rope light.

[-klb-]

One of the big differences in LED and incandescent lighting, is that incandescent sheds much of its heat as Infra Red light, which heats up stuff away from the bulb. LED lights do generate much less heat, but shed almost none of it as IR light. So nearly all the heat they produce is heating things up locally. So air cooling is important to the LED lights. You can get by with much a much longer plugged in time on a roll of LED rope light than incandescent, but yes, it is still not something you want to do for more than a few minutes.

[LOR Staff]

There is an easy way to remember this:

If it uses electricity, it generates heat. No exceptions.

If you think about it at the atomic level, and I'm no scientist, so this is going to be a bit simplistic, heat is nothing more than the measurement of how fast things (atomic particles) are moving. If electrons are moving, then by definition they have heat. If you force them to move, for example you push them through a semi-conductor to produce light, you increase the amount of heat.

Yes, LEDs run COOLER, but they do not run COLD.

[Dennis Cherry]

Even LOR with the CCR's states you should not operate the Ribbons while coiled up, Why? Heat.

Rope lights are next on the list to not operate coiled up. Reason? Heat.

Do not blame the LED's.

[jim6918]

Even LOR with the CCR's states you should not operate the Ribbons while coiled up, Why? Heat.

Rope lights are next on the list to not operate coiled up. Reason? Heat.

Do not blame the LED's.

Not blaming the LED's by any stretch. A totally stupid act on my part.

[Dennis Cherry]

Not blaming the LED's by any stretch. A totally stupid act on my part.

That's OK.

Just did not want new members think LED's normally get hot enough to catch on fire.

[Orville]

As much as folks want to believe LED's generate some heat, they really do not. They do run cold, IT IS NOT the LED itself that generates the heat, it is the CIRCUITRY behind the LED that creates the heat and the fires, I've been using LED's in projects for many years, they have never gotten hot providing the proper current ~AC~limiting circuitry is in place.

I bought an LED replacement bulb when they first came out, it would screw in to a standard C7 night light fixture, this LED fixture got RED HOT, which should never occur! So I took it back and got my money back on it. As an LED bulb should always be COOL to the touch, never hot and shouldn't even be moderately warm. And the newest ~AC~ night light LED replacements are very cool to the touch, they don't even get remotely warm, which means the circuitry to drive the LED off 120VAC has been redesigned to work properly WITHOUT that heat generation. {unfortunately ti seems the Halloween. Christmas LED strands and LED Rope Light manufacturers still haven't gotten this exactly right}.

Where the heat comes from is in the design of the circuitry that drives them, especially if ~AC~ powered and using rectifiers to convert that ~AC~ to either half or full-wave DC to run the lights on 120VAC is where the heat is first generated, and since these "blobs" generate heat, if they are coiled, that heat is now impacted in a way that there is no air flow around the circuit that controls the LEDs themselves.

I've noticed this with just about every LED strand of lights I have, the blob is the warmest part of the strand, if coiled that little blob gets even hotter, but the LED itself is never hot or even moderately warm to the touch.

In the case of rope light, the circuit is more than likely embedded inside the rope itself, this also creates more heat from the blob because there is no true air-flow inside the rope tube, otherwise it wouldn't be weatherproof. Unfortunately when coiled, this heat is entrapped even more and so, the rope LED gets hotter and hotter until it reaches the point of starting to melt the rope exterior rubber and possibly start a fire when left in a coiled position. It's also why I never test or leave anything in a "coiled" position, but stretch it out..

But that's why heat is something to definitely take into consideration when using LED items or building LED projects, the better airflow you have around the LED, the less likely of a heat or failure issue of the LED itself.

BTW: this is the "condensed" version as there is a lot more to it than this, but trying to keep this as short as I can and within a nutshell.

[LOR Staff]

The AC/DC thing is incorrect.

ANY movement of electrons, be they ALTERNATING or DIRECT generates heat. NO EXCEPTIONS. Ok, there is one exception: a PERFECT conductor will not heat up when electrons move through it. As of right now science has not found a perfect conductor, and 'Super' conductors:

1. still generate heat
   
2. are still exotic enough to not have found their way into normal people's hands
   

Now, it is true that most rectifiers/transformers/current limiting resistors and the like can be more ineffient than an LED would be, and that is why those are 'warmer' than the LEDs themselves. But that is not always true.

If you care to test this, I have some CREE led modules that I will be happy to hook up with nothing more than a current limiting resistor and 3 D-Cell batteries. I'll grab hold of the resistor and batteries, and you can grab hold of the LED's heat-sink. First one that screams looses

[Santas Helper]

I'm just curious. If Jim is from Colorado, why did he mention Virginia? Is that state form or female form?

Might explain the heat-up

[james campbell]

I'm just curious. If Jim is from Colorado, why did he mention Virginia? Is that state form or female form?

Might explain the heat-up

maybe that means they stay cool in Arizona

[edvas69]

By powering up lights or cables that are coiled up is like creating a big electromagnetic coil, now if electromagnetic coils are left on with no solenoid piece in the middle then these get very hot and will burn out. So the same theory applies to rolls of LEDs, and extension cables. The more coils and the tighter the coils radius the more heat that will be generated.

[jim6918]

I'm just curious. If Jim is from Colorado, why did he mention Virginia? Is that state form or female form?

Might explain the heat-up

Ha Ha Ha. Thanks I needed a good laugh out of this situation.

[Max-Paul]

I consider only one of the above to be close to the truth. Gents first lets not forget even LED rope lights rely on resistors to limit the current flowing through the LEDs. yes the leds will produce some heat, but the majority of the heat will be in the resistors. There is ZERO inductance effect causing heat. Even the CCR uses resistors. IR emissions is questionable so I wont discount this as a possible effect. But again the resistors are the main source of heat in rope lights. Take a close look at your rope lights. And you will see that it is not just one resistor per meter or what ever the length is between cut marks. So, lets say that the section requires 5K ohms and 1.5 watt rated resistance. What they will do is select a resistance value close to 625 ohms and 1/8 watt. But any time voltage is restricted by some form of resistance. The voltage and current through that source of resistance will heat up.

Sorry but after posting this, I felt that more needs to be said. Lets say that you have 30 bulbs or 30 LED over a 30" cut length. Now lets say this is a white LED and ican rope light. White LEDs drop 3.3v per LED. So those 30 LED summed will come to 99V. The peak voltage not RMS that your volt meter reads is like 150vpk. So those resistors need to drop 51 volts @ .02A. Watts law says voltage X Current = watts. So in this case we are looking at 1.02 watts.

Ok, lets look at an Ican rope light. Each bulb is rated at say 5 volts. So 5 X 30 = 150 volts. Wont need any resistors. But we would need to look at the power drop across each bulb. It is safe to say that the current draw is going to be higher than .02A. Lets just pull a number as an educational guess. I am going to say close to .05 might be higher. So, 5 X .05 = .25 watts each bulb. While a white LED is 3.3v X .02A = .066W per LED

Edited August 22, 2012 by Max-Paul

[edvas69]

I consider only one of the above to be close to the truth. Gents first lets not forget even LED rope lights rely on resistors to limit the current flowing through the LEDs. yes the leds will produce some heat, but the majority of the heat will be in the resistors. There is ZERO inductance effect causing heat. Even the CCR uses resistors. IR emissions is questionable so I wont discount this as a possible effect. But again the resistors are the main source of heat in rope lights. Take a close look at your rope lights. And you will see that it is not just one resistor per meter or what ever the length is between cut marks. So, lets say that the section requires 5K ohms and 1.5 watt rated resistance. What they will do is select a resistance value close to 625 ohms and 1/8 watt. But any time voltage is restricted by some form of resistance. The voltage and current through that source of resistance will heat up.

Sorry but after posting this, I felt that more needs to be said. Lets say that you have 30 bulbs or 30 LED over a 30" cut length. Now lets say this is a white LED and ican rope light. White LEDs drop 3.3v per LED. So those 30 LED summed will come to 99V. The peak voltage not RMS that your volt meter reads is like 150vpk. So those resistors need to drop 51 volts @ .02A. Watts law says voltage X Current = watts. So in this case we are looking at 1.02 watts.

Ok, lets look at an Ican rope light. Each bulb is rated at say 5 volts. So 5 X 30 = 150 volts. Wont need any resistors. But we would need to look at the power drop across each bulb. It is safe to say that the current draw is going to be higher than .02A. Lets just pull a number as an educational guess. I am going to say close to .05 might be higher. So, 5 X .05 = .25 watts each bulb. While a white LED is 3.3v X .02A = .066W per LED

You are correct mutual inductance doesnt play a direct part in the heating. For some reason i had that thought until i looked it up. The best description of why this happens may be found here http://uk.answers.yahoo.com/question/index?qid=20100520125802AAs2Ufo

[-klb-]

The other thing, is that while LEDs are way more efficient at turning electricity into light that incandescent, and even fluorescent, they still only turn about 30% of the power into light. The remaining 70% goes into heat. But you are putting out 10 times the light for the energy compared to incandescent, so you are generating less than 10% as much heat for the same light. But again, that heat is localized, and only cooled by conduction.

Yes, the limit resistors and wiring contribute to the effect, but by the time you are dealing with high power LEDs, just by themselves, they are putting out enough heat that you have to heat sink them, or they thermally destroy themselves.

[Guest Don Gillespie]

Jim the most important thing in all this is that you caught it before it did any damage, thanks for bringing it to everyones attention, even though some people think it will be ok we always seem to learn a new lesson, glad your ok and nothing got burnt down.

[magish01]

Okay, after reading all the above, I think my feeble mind understands.....something about LED's gets hot enough to possibly start a fire. Don't really think it matters what actually causes the heat. Don't leave items coiled and on as flames could be a result.

Except in Arizona. That place is HOT! So everything else seems cool.

[Santas Helper]

I'm still waiting on the Virginia thing.