More heat than light? Incandescent vs CFL vs LED

Status
Not open for further replies.
Joined
Sep 25, 2009
Messages
18,133
Location
OH
Everyone knows that a lot of the electricity consumed by an incandescent lamp is resolved into heat.
This is also true of CFL and LED lamps, with both requiring heat sinks that do get quite warm in use. I had always thought that LED lamps would remain quite cool in use and I was always wrong about that.
My guess is that the primary energy savings in moving from incandescent to CFL and then LED lamps was in reduced heat output relative to the output of light.
If this is so, are there lower heat emitting lighting systems on the horizon which could be far more efficient?
 
Good question and I have hoped there would be.

LED's have to be Pulse Width Modulated (PWM) by switching transistors so the switching transistors do dissipate a certain amount of heat, but the overall circuitry verses light output is still a more efficient system in my view.

9.8 Watts power consumption verses 60 Watts for the same or greater (and more pleasing) light output is plus in my book.
 
Originally Posted By: MolaKule

9.8 Watts power consumption verses 60 Watts for the same or greater (and more pleasing) light output is plus in my book.


Agreed on both counts.
Really like LED lamps and never was as fond of CFLs although we still have a few in service. We even have a few vintage incandescent lamps where they see almost no use, like in closets.
 
They all have there place. I'm waiting for light emitting panels that can be built as a wall and use 10w for the whole wall and last 50 years
laugh.gif
 
I don't think we've ever gotten a decade of use out of any CFL, but in fairness they were the best energy saving option of the day when introduced as well as for a number of years thereafter.
Only recently have LED lamps become cheap enough to be a viable choice. If you happen to get a bum one, you just replace it for the couple of bucks they now cost, cheaper than sending it off to get a warranty replacement.
Back in the day, one kept stocks of incandescent lamps on hand since they had much shorter lives than any CFL much less LED lamp.
 
The problem with CFL, and I suspect LED too, is the power electronics. We know fluorescent tubes last a LONG time... But the electronics are where both the (generally poorly mitigated/managed, resulting in low life) heat source is, and thus the reliability issues stem from.

I guess with LED, since the light is more of a point source and much smaller area than a tube, the manufacturers took more liberties to make larger heatsinks that should enhance life, hopefully. So far, so good.
 
Originally Posted By: JHZR2
The problem with CFL, and I suspect LED too, is the power electronics. We know fluorescent tubes last a LONG time... But the electronics are where both the (generally poorly mitigated/managed, resulting in low life) heat source is, and thus the reliability issues stem from.


This is exactly what the issue is. As they had to lower the cost of them as time went on, the quality declined at the same rate. Old, well built CFLs lasted a long time. I'm not saying they were an awesome light source, but they lasted much longer than today's flimsy, super light weight units.
 
LEDs are increasing efficiency at a very good rate ... the units available in five years will generate half the heat for the same light output at those available today, and those are very much advanced over LEDs of the past.

If you lose a light source this morning, you need to replace it today, not five years from now. So use what is available.

It should be noted that light efficiency is based on the assumption that heat is an unwanted side effect of operating the device. If you live in a northern climate, or you have lighting in an area of the home that is unheated but less than 68F, then the heat output is ** wanted ** output, not unwanted output. Thus the least efficient type is now 100% efficient, as both the heat and light are wanted output.

Electrical heating is 95% or better in efficiency. If you have one of the latest super-high efficiency natural gas furnaces you can equal that. Where electric heat is inefficient compared to the most recent Natural Gas heater technology is at the Power Plant, which can be as little as 70% efficient but also could be higher, depending on how your local utility generates electricity. Now it's a matter of your Natural Gas heater (how old is it?) versus your Power Plant (is it nuclear? Very efficient) as far as what is least damaging to "the Planet". Older furnaces can be less than 70% efficient.

If the area is one that uses supplemental heat ... ie you have a Natural Gas furnace and the lamp is in an area heated by that furnace, then changing to a more efficient bulb will mean you will use more Natural Gas to replace the lost heat provided by the lamp. So you have gained nothing; you reduce one bill and increase another for the same net result.

Ideally you would use incandescents in winter and switch to LEDs when the air temperature is above about 70F, and back to incandescents in the fall. But of course regulators realize no-one will do this, so they ban incandescents and conveniently fail to mention the increase in winter heating load that will result.

As always, it's not the information you get that matters, it's the information held from you that matters.
 
Originally Posted By: edwardh1
the lighting industry should be ashamed of the cfl hoax, "it will last 10 years etc etc.


I have CFLs going 13+ years right now.

The biggest issue was old housings and wiring that was slightly out of spec. CFLs, and LEDs to a degree, are sensitive to off voltage and/or fluctuating voltage, esp for the cheaper ones. I installed all new housings and rewired my house after we bought it. Never had issues with CFLs burning out early and even have some on my porch where they are not rated for yet still going 10+ years later.
My oldest VFLs are ones we used at out last house and brought with us. They have got be at least 13years old but many are still going. Many died due to using in the old housing/wiring and/or being painted when we gutted the place.
 
Originally Posted By: Johnny2Bad
LEDs are increasing efficiency at a very good rate ... the units available in five years will generate half the heat for the same light output at those available today, and those are very much advanced over LEDs of the past.

If you lose a light source this morning, you need to replace it today, not five years from now. So use what is available.

It should be noted that light efficiency is based on the assumption that heat is an unwanted side effect of operating the device. If you live in a northern climate, or you have lighting in an area of the home that is unheated but less than 68F, then the heat output is ** wanted ** output, not unwanted output. Thus the least efficient type is now 100% efficient, as both the heat and light are wanted output.

Electrical heating is 95% or better in efficiency. If you have one of the latest super-high efficiency natural gas furnaces you can equal that. Where electric heat is inefficient compared to the most recent Natural Gas heater technology is at the Power Plant, which can be as little as 70% efficient but also could be higher, depending on how your local utility generates electricity. Now it's a matter of your Natural Gas heater (how old is it?) versus your Power Plant (is it nuclear? Very efficient) as far as what is least damaging to "the Planet". Older furnaces can be less than 70% efficient.

If the area is one that uses supplemental heat ... ie you have a Natural Gas furnace and the lamp is in an area heated by that furnace, then changing to a more efficient bulb will mean you will use more Natural Gas to replace the lost heat provided by the lamp. So you have gained nothing; you reduce one bill and increase another for the same net result.

Ideally you would use incandescents in winter and switch to LEDs when the air temperature is above about 70F, and back to incandescents in the fall. But of course regulators realize no-one will do this, so they ban incandescents and conveniently fail to mention the increase in winter heating load that will result.

As always, it's not the information you get that matters, it's the information held from you that matters.
When you're promoting an agenda you can't put out all the information and water down the narrative. Incandescents are always bad all the time. I wonder what the ACTUAL overall energy savings are in a colder climate.
 
Originally Posted By: Jimzz
Originally Posted By: edwardh1
the lighting industry should be ashamed of the cfl hoax, "it will last 10 years etc etc.


I have CFLs going 13+ years right now.

The biggest issue was old housings and wiring that was slightly out of spec. CFLs, and LEDs to a degree, are sensitive to off voltage and/or fluctuating voltage, esp for the cheaper ones. I installed all new housings and rewired my house after we bought it. Never had issues with CFLs burning out early and even have some on my porch where they are not rated for yet still going 10+ years later.
My oldest VFLs are ones we used at out last house and brought with us. They have got be at least 13years old but many are still going. Many died due to using in the old housing/wiring and/or being painted when we gutted the place.
I have some CFLs that have lasted a long time. Also had some that didn't. Unless the ones I currently have last 30 years the avg life isn't going to be that great. The one bulb design that seems to be the worst life is the halogen replacements. That experiment of mine failed.
 
Last edited:
This is a good point.
For about six months of each year, the byproduct heat of any lamp is desirable and clearly must radiate into the heated spaces of the house.
Never really thought of it that way, but it seems that the heat generated by any lamp isn't a waste at all, although I suspect that it's cheaper to obtain the same BTUs from our boiler than it is from our lighting.
 
The gentleman sitting next to me on the airliner was an executive at Phillips LED lighting division. He claims that they have white LED's with nearly 300 lumens output per watt. Possibly coming in a few years. That kind of efficiency would make an LED 60w equivalent bulb consume only about 3 watts.
 
Impressive, but we expect rapid improvements in electronics, which LED lamps are.
More impressive to me is that you actually got into a discussion of lighting efficiency with a seatmate on a commercial flight.
How in blue blazes did that happen?
 
Originally Posted By: Cujet
The gentleman sitting next to me on the airliner was an executive at Phillips LED lighting division. He claims that they have white LED's with nearly 300 lumens output per watt. Possibly coming in a few years. That kind of efficiency would make an LED 60w equivalent bulb consume only about 3 watts.


Best I've seen so far is about 8.5 watts for an 800 lumen bulb so that'd be pretty good. You normally just go by the electricity used for the same amount of light. Typically on a CFL 60 watt, it was either 13 or 14 watts and anywhere from 9-11 watts on an LED. If they're on 24/7, eventually even if the CFL is free, the LED is cheaper. I have some CFLs that are about 11 years old. Key to those is that they're on 24/7 as back hallway lights and I think the building has only lost power a couple of times. Basically they didn't wear out because they were never really turn on and off much at all. I actually have a spare one of those bulbs and it was only rated for 6000 hours, it's probably pushing 100k hours.
 
Have they figured out how to take the blue tint out of the LED light ? I get the CFL Sylvania bulbs in a soft white from Lowes. They put out kind of a yellow'ish light. Easy on the eyes.
 
Originally Posted By: Merkava_4
Have they figured out how to take the blue tint out of the LED light ? I get the CFL Sylvania bulbs in a soft white from Lowes. They put out kind of a yellow'ish light. Easy on the eyes.


Most definitely. This was the struggle years ago. Any color rendering you want now.
 
Originally Posted By: Johnny2Bad
LEDs are increasing efficiency at a very good rate ... the units available in five years will generate half the heat for the same light output at those available today, and those are very much advanced over LEDs of the past.

If you lose a light source this morning, you need to replace it today, not five years from now. So use what is available.

It should be noted that light efficiency is based on the assumption that heat is an unwanted side effect of operating the device. If you live in a northern climate, or you have lighting in an area of the home that is unheated but less than 68F, then the heat output is ** wanted ** output, not unwanted output. Thus the least efficient type is now 100% efficient, as both the heat and light are wanted output.

Electrical heating is 95% or better in efficiency. If you have one of the latest super-high efficiency natural gas furnaces you can equal that. Where electric heat is inefficient compared to the most recent Natural Gas heater technology is at the Power Plant, which can be as little as 70% efficient but also could be higher, depending on how your local utility generates electricity. Now it's a matter of your Natural Gas heater (how old is it?) versus your Power Plant (is it nuclear? Very efficient) as far as what is least damaging to "the Planet". Older furnaces can be less than 70% efficient.

If the area is one that uses supplemental heat ... ie you have a Natural Gas furnace and the lamp is in an area heated by that furnace, then changing to a more efficient bulb will mean you will use more Natural Gas to replace the lost heat provided by the lamp. So you have gained nothing; you reduce one bill and increase another for the same net result.

Ideally you would use incandescents in winter and switch to LEDs when the air temperature is above about 70F, and back to incandescents in the fall. But of course regulators realize no-one will do this, so they ban incandescents and conveniently fail to mention the increase in winter heating load that will result.

As always, it's not the information you get that matters, it's the information held from you that matters.


There is an exception to your story and that is if you have a heatpump based heating.
Heatpumps provide much more than 100% efficiency in heat per watt of electricity used by including the outside environment as part of the thermodynamics equations. Most heatpumps should have at a minimum of over 100% efficiency except in the most extreme climates.

If you are doing the thought experiment of switching your light bulb type in the name of efficiency, this doesn't make sense, you should instead think even further outside the box (literally thinking outside the house as a closed system) and jumped to a heatpump based heating solution, which then renders all that busywork of swapping lightbulbs seasonally a moot point.
 
Last edited:
I'm quite interested in the power plants that can be "as little as 70%" efficient...there's scarce few that are even knocking on 70%.

Using lights to heat your house doesn't make sense when you can use gas (and certainly yes, heatpumps).

But as I explained to author Paullina Simons, over lunch in NY one day, 10 150W incandescents running 24/7 is both a poor way to heat a house, but a massive double burden the day you need the air-con.
 
Status
Not open for further replies.
Back
Top