if LED lights are so efficient then why do they get almost as hot as incandescents?

[BirdDad]

mine get too hot to handle and I have tried from three different manufacturers.

 

[KWiklund]

There are still inefficiencies in the electronics and that results in heat. However, it is still much less heat that is generated in an incandescent bulb. For example, the filament in an incandescent bulb is heated to about 2500 degrees Centigrade, and it is the heating itself that produces light. The processes that produce light in an LED bulb are much more efficient, but heat is still produced since no conversion is 100%.

 

[AD5MB]

the ratio of light produced versus heat produced is where the efficiency can be found

 

[LoveMachine]

Try twisting out an incandescent after it's been on for >10 minutes. Blisters on the fingers. An LED certainly won't be comfortable, but no trip to the burn ward.

 

[Jeff7]

Incandescent: A filament is heated to a few thousand degrees. It gets so hot that it puts out visible light. The objective here is to ensure that that hot filament stays safely inside the bulb, mainly so that it doesn't set your house on fire. That's why you'll see the warnings on fixtures: "Do not use exceed a 75W bulb in this fixture." If you do, there can be excessive heat buildup in the fixture to the point that it will be damaged, or you'll have a fire.
The overwhelming majority of energy going into an incandescent light is turned into heat right away. A very small amount of it is turned into visible light.

LED: The junction temperature of the emitter itself is usually going to be rated to a maximum of somewhere around 135°C (275°F), but it's preferable to keep the emitter below 85°C (185°F). The cooler it can be kept, the longer it will maintain its light output. So with LED, the idea is to get as much heat away from the emitter as possible. That's why you'll end up with a hot casing of an LED lightbulb. The casing is hot because it's trying to dissipate the heat of the electronic driver circuit and of the LEDs themselves. The unfortunate fact is that the common Edison screw-in socket was not made with the goal of efficient heat transfer in mind. LED lights have to do whatever they can to keep the emitters cool. Early on, this meant simply using fewer LEDs and driving them with less power, so those lamps were often dim. (Or some manufacturers would simply run the LEDs at excessive temperatures, resulting in greatly diminished product life.)
This is a lamp that looks like it was designed with LEDs in mind. The reflector should have been designed assuming a single emitter source at the base, rather than a bulb in the middle, and there's a big heatsink in the back.

Why is it still hot? LEDs also aren't very efficient when you look at energy-in versus energy-out and visible light. I've got a design guide here from Philips (I work with LEDs) that was published in 2010. It shows that LEDs convert 15-25% of the incoming energy into visible light. The rest of the energy is lost as heat, either due to internal voltage drop in the die, or because the emitter die itself is highly refractive, which causes some of the generated light to reflect back into the die rather than leave. That light strikes the die and heats it up.
That's for a white LED. A white LED is made up of a blue emitter with a phosphor coating. The blue light hits the phosphor coating, which in turn fluoresces and emits yellow light. Some of that light is simply absorbed though, which heats up the phosphor. Some of the blue light also passes through. Your eyes see this mixture of blue and yellow light as white light.

So you've got heat losses in the electronics to regulate the power that the LEDs need, losses in the emitter die, and losses in the phosphor. To keep all of that stuff running properly, the heat needs to be removed.
Even after all those losses, LED is still better than incandescent.




Your LED bulb also feels hot because it's likely made of aluminum.
If you have a block of warm wood and a block of warm aluminum, both at the same temperature and warmer than body temperature, the aluminum will feel much warmer than the wood. That's because the aluminum is a better thermal conductor. The wood is an insulator. So the aluminum is going to freely dump its thermal energy into your hand, whereas the wood is not able to.
It's the same reason why a metal pot sitting unused on a shelf will feel colder than a plastic container in the same room. The metal is a good conductor, so it will more freely absorb thermal energy from your hand, and that in turn cools down your hand and the nerves in it, which makes it feel colder than the plastic of the same temperature.

 

[inachu]

I own 10 LED lights and they are not hot at all.

 

[Revolution 11]

To add to Jeff7's comments, the current efficiency of LEDs is around 15-25%. But you can expect that figure to rise. Current cheap mass-market 60W-equivalent LEDs are around 70-100 lumens/watt.

We are already approaching 200 lumens/watt in the next two generations of LEDs. The theoretical max efficiency for LEDs is around 300 lumens/watt. The max theoretical efficiency for an ideal light source (Green light at 555 nm) is 683 lumens/watt.

 

[Red Squirrel]

It's not the LEDs that get much hot it's the power converters. It still ends up using less power than other lights though but they could be even better if there was a central DC conversion point that then powers each LED in the house instead of each bulb having it's own power converter.

Idealy they should make a lighting standard where you have a central rectifier at the electrical panel with it's own breakers for LED lighting circuits. -48v nominal (could run at -54 to enable adding backup batteries) would probably be a nice voltage.

I don't think the light bulb companies would be for such a standard though. You'd practically never ever have to replace a bulb again once you decide on your lighting and install them. Even now I don't think it's that often that a LED fails. The converters arn't THAT complicated so not that much that can fail. Maybe capacitors.

 

[probedb2]

I've found it to be the electronics around it that get hot or fail, even the more expensive ones. The LEDs themselves are never hot. The electronics need decent heat sinks really and the better quality bulbs seem to make this part of the design of the bulb. It works well for bayonet style bulbs that I use.

 

[edro]

The LEDs get very hot.
55C, 85C and 105C are common industry design guidelines, but that is not nearly as hot as an incandescent filament.
The housing is a heat sink, so it will be hot.
A hot heat sink is a good thing. It means the heat sink is doing its job and the LED heat is being pulled away well.

But don't worry, as long as the LED bulbs are made by a decent manufacturer, they will be well within their temperature limits.

60W incandescent lamp bases are rated to at least 200C, so you have nothing to worry about.

 

[William Gaatjes]

In terms of saving energy, a led lamp is a good investment. I pay very little for my electrical bill, and still i get money returned every year simply because of my energy efficient electrical appliances. If you want to save money and the environment, it does make a difference.

 

[John Connor]

Florescent lights create heat too, but nothing that will burn your hand I reckon.

 

[Berliner]

Also LEDs are smaller, which in turn will concentrate the heat to a smaller surface.

 

[ctbaars]

I own 10 LED lights and they are not hot at all.

Here too. I have a digital dimmer. Sometimes my bathroom is too bright for me so I use my digits to unscrew a bulb or two of the three in the fixture. They get hot if on for a while but I have no trouble handling them in the socket. Don't try this with incandescent bulbs.