OK, I have pretty much replaced all of my old CFL bulbs in the house with new 9 W LED bulbs. They still produce some warmth, though. My question is this: Which produces most of this heat? Is it mostly produced from the LEDs in the bulbs, or from the conversion of the 120 VAC current into current suitable for the LEDs, and in what relative amounts?
The power supplies are close to 90% efficient - most of the heat is from the LEDs themselves, which are only 25% - 30% efficient or so.
Years ago, we would use infrared LED illuminators with tube-type video surveillance cameras. The efficiency of the LEDs was much lower than today and the units had huge heat sinks to help dissipate the heat produced solely by the LEDs. This was true even when the units were DC-powered by a separate power supply.
LEDS are efficient at producing light, so require low power, but what heat they do generate needs to be dissipated to protect the circuitry. This is still a design issue and cheaper designs may skimp on this and have a shorter life.
I used to think of LEDs as very efficient, until someone wired up an ultra-high output LED to a circuit board and cranked it up to full power. It got so hot that it melted the solder holding it onto the board, and fell out. This cut the circuit and turned off the LED, which was a good thing, because that sucker was bright.
LEDs ARE more efficient at turning electrical energy into useful light that we can see, because most of its output doesn’t go into the infrared, as with incandescent bulbs. But fluorescent lights are still more efficient. The edge LEDs have is that they’re physically robust. You can bounce an LED “bulb” with a plastic housing off the ground, while compact fluorescent will shatter, scattering mercury.
We moved into a new house about two years ago and except for a couple CFLs the previous owner didn’t consider taking with him, all of the lamps had to be installed so we did so with LED bulbs. My brother bought a carton of twenty at CostCo; they were by Feit so I don’t know how cheap they might have been but at least it’s a brand you have heard of. So far, four have failed. Two were lights that were on a fair bit but base down, two in lights used maybe 200 hours but were base up; none of them anywhere near the 50,000 hours the box promised. I dunno if we’re seeing the beginning of a bathtub curve or not but the failures were replaced with dollar store lamps.
Back in the day I had trouble getting the promised hour out of base up CFLs and besides the durability CM mentions, there’s the PITA of disposing them properly to keep their – admittedly small amount – mercury out of the environment. I saw a cite that even if the lamp’s mercury escaped, it was smaller amount than that emitted by coal-burning power plants during it’s lifetime due to their efficiency. I was dubious of the claim.
I didn’t realize they were so low. Do you know the efficiency of tungsten incandescent?
This also surprises me. I have been replacing my CFLs with LEDs when they need replacing. Part of the reason is efficiency but a bigger part is I am expecting them to have a longer life. Hasn’t always been true, though.
The last time I went light-bulb shopping, a couple of months ago, for a given “equivalent incandescent rating” (i.e., brightness), the LED bulbs were all lower wattage than the compact fluorescents. And I don’t think they were fudging the numbers, because the only one I’ve installed so far actually seems to be brighter than the incandescent that was in that fixture before. Which would mean that LEDs are more efficient than compact fluorescents.
It’s difficult to compare because it depends upon definitions. And I notice that the websites are somewhat biased, but it appears that LEDs have gained significantly over compact fluorescent bulbs in recent years. The compact fluorescents have been phased out in their favor, although I suspect a large part of the favor for LEDs is that they’re less fragile and don’t contain mercury. (They also don’t require any sort of warm-up, and work well with dimmer switches) But by a lot of measures LEDs are now more efficient that compact fluorescents. So you’re probably going the right way.
Incandescent lamps are somewhere between 2% and 10% efficient. A “long-life” (undervolted) lamp has horrible efficiency, while a studio Photo lamp might be approaching 10%, at the expense of very short lifespan. Halogen lamps are better, but I don’t think they get past the 10% range.
Interestingly, I also recently got an “efficiency package” from the local electric company, with a variety of low-power-consumption bulbs and a couple of other doodads. All of the bulbs were LED, except for the three-way bulb, which is still fluorescent. I’m guessing that that’s because an LED three-way would have trouble getting enough heat rejection?
I have designed a light bank in the past and the official factory figures for GE halogen projector lamps were 90% infrared, 1% ultraviolet and 9% visible light. At that time the low voltage projector lamps were the most efficient you could get. They had dichroic coatings on the reflectors to allow IR to pass through to the rear and only the visible light was reflected.
Dennis
I know it used to be true that, for white light, fluorescent was more efficient than LED. I would like to know if this is still true. I have heard folks mention white LED is now more efficient than fluorescent, but I would like to see some numbers.
While LEDs are more efficient at producing light and produce less heat per watt than stone age type incandescent bulbs they also have much less surface area to dissipate the heat they do produce. The situation is improving as high rate blinking and using more LEDs running at less than capacity reduce the problem. It would be a great thing to solve all the heat dissipation problems because it is only the heat that reduces the life of the devices from what would be virtually a lifetime.
Old school (10 yrs ago) LED rule of thumb: The majority of heat was produced from power supplys. At that time, the LED outputs were minimal, tending to run cool and the supplys were unsophisticated and ran hot. Nowadays, the opposite is true. Power supplys are much better, and the outputs of the LEDs have increased tremendously. IIRC: The LED power/heat curve isn’t linear. Higher output LEDs tend to run at a dis-proportionately higher temperature than the lower powered ones. Now the LED “bulb” units (in commercial fixtures at least) require substantial heat sinks in and of themselves.
From Wikipedia:
Commercial LED A19-replacment lamps are running at 85-100 Lumens/Watt. Higher CRI lamps are less efficient. If you are willing to put up with slightly lower CRI light, then you can find lamps in the 125+ lumens/Watt range. Raw LEDs are approaching the theoretical white-light efficacy limit of 300 lumens/Watt.
Philips claims a 200 lumen/Watt lamp: Philips and Dubai unveil world's most efficient LED bulb
One thing I’m unclear on…
Are the comparative ratings tossed about here (and in mfgrs. specs) “apples to apples” so to speak?
In other words, are we talking pre-power supply, or post-power supply current draw specifications? The difference could be important in determining efficiency. Not to mention different “qualities” of light (wavelength).
What you want is “wall-plug efficiency”
Yes, comparing just the bare emitters (LED, Fluorescent tubes, Sulphur-globes, etc.) isn’t very helpful. The stated lumens/watt on commercial lamps is wall-plug efficiency, and includes power supply losses.
Note that some cheap (and not-so-cheap) LED fixtures use inexpensive power supplies that have reasonable efficiency, but crummy power-factor. Probably not a concern for the home, but might be if installed in huge quantities in a commercial setting.
All over the country, they are still building office buildings & commercial stores with fluorescent tubes for lighting. They are cool, efficient, and good enough for their purpose.
They have several advantages for this use:
- they light up the whole floor area (not just certain parts of the room, like in houses).
- they are turned on in the morning, and stay on all day long (no switching on and off)
- they are mostly located out of reach, and tubes are replaced by trained staff (so fragility isn’t very important).
- they are cheaper for a contractor to purchase & install.
how are they measuring the luminous efficacy? the one disadvantage CFLs have is some of the power they consume lights the inside of the “swirl” and doesn’t contribute to lighting the surrounding area. LEDs can be arranged so they “throw” their light primarily in the desired direction.