so I decided to try some led bulbs from walmart—- the 8.5w non dim marbles were pretty cheap so why not? well I was totally surprised by the “dimming” when they are turned off—-not instant like I expected but more like when you turn off an incandescent high beam on a car. why is that happening?
LED’s run on DC current, so the bulb has a AC to DC power supply in the base which includes a filter capacitor so that the LED’s don’t flicker 60 times per second. For this to be effective the time constant for the circuit has to be substantially larger than the frequency period (16.67 ms for 60Hz), typically on the order of 10 times. So when the current is switched off, the capacity slowly discharges through the LED array. My thumbnail says it should take about 1/3rd of a second from time you turn the switch off until the LED is effectively “out”.
aaah. ok I had no idea … the bulb/globe is cool
but the lower portion is HOT. thanks for the info!
Transforming 120v AC to 12v DC (seems to be a common used voltage) produces some heat. How hot it gets depends on the heat sink design and build quality.
As an electrician I’ve been against installing most of the common “screw in” type LED retrofits for some time because of the problems most manufactures have had with trying to fit a heat sink that works into a universal preexisting space and still producing a product that will sell at a price most people can stomach. A lot of preexisting fixtures were not designed with the proper airflow for the heat sinking, think of the ones with a globe that covers the bulbs. In the early days I’ve seen the bulb bases get hot enough to burn up the lamp socket. Often I have to make sure the customer understands my warranty only covers my work and installation and they have to go to or have me go to the manufacture for product warranty.
As an LED enthusiast and supporter I try out all kinds of do-dads and new gimmicks. With my electrical background I can geek out and make sure I keep an eye out on them. Just like we do on our flashlights modifying or trying to fix problems as the arise.
In the past few years the technology has started to gain ground and I’m seeing more and more easily accepted priced products that are of better quality. Still nothing I will stand behind 100% as a drop in and forget it but its looking better.
Some LEDs also glow slightly for a second or two after the power’s turned off, I think that’s called “persistence” — it’s a characteristic of some of the phosphors used.
yes the heat concerns me but then again I havent felt an incandescent bulb in a while, so it might just be that I’m used to the cfl’s being so cool…
I’ll probably get out the temp probe on my DMM and see what it is at, and then compare it to a 60w incandescent.
Joel, when you are taking temps would you mind also measuring a CFL? It would be interesting to know incan, CFL and LED.
I’ve not yet known of a fixture socket fail due to LED bulbs and If it did, it would have similarly failed with an incan. Think this through- an Incan is around 30% light and 70% heat so a 100W incan makes 70W heat. IIRC the equivalent LED bulb uses around 13W (don’t quote me on that, on my first cup of coffee this morning) and it’s far more efficient. But for the sake of argument let’s say it turns that whole amount of energy into heat. It’s less heat than the equal Incan
With an Incan, the metal base and glass globe are glued together so the entire surface is a heat sink. With a LED bulb less than half that surface area for sinking exists so the heat at the base might possibly be double. In our 100W example above that’s still a maximum of 26W heat possible from the LED bulb and we’re still well below the Incan’s 70W of heat- and this is still totally discounting the LED’s far higher efficiency.
I install lots of fixtures in my work. I too have seen plenty of fixtures with apparent heat damage to the sockets but I’ve been seeing that for decades, long before LED and CFL bulbs came along, therefore that is not being caused by the LED bulbs but by substandard fixture sockets. I’ve noticed that trend correlates to being found mostly cheaper fixtures, even open ones where air circulation can aid cooling. Moreso with the newest cheapest ones being sold at the ‘big box’ stores (which are almost all made in China BTW). So IMHO this problem is unrelated to LED bulbs and those sockets would have failed regardless.
Given all this I’d love to see the results of an actual test comparing the heats of the different technologies of bulbs, both overall heat and that of the socket areas. I’d be surprised to find anything different than what I stated above. Definitely subscribed!
Phil
It all comes down to wattage…
An incandescent bulb is pretty muchly, nothing more than a space heater at a rated wattage. Most sources I can find rate incans at 3-10% efficiency.
A 60W incandescent bulb will be dumping about 55W of wasted heat back into your home.
A 60W-equivalent LED bulb (using the $2 bulbs from Lowe’s), operates at 9-10W only. Even if these bulbs were operating at 0% efficiency (i.e., no light at all), you would still end up with only 10W worth of heat-energy. That’s the same amount of heat as you would get from a 10W-driven XM-L flashlight left tailstanding in a room.
This is why I prefer the CFL/LED bulbs. In East Texas, Summers are long, with daytime temps over 100°F/40°C, nighttime temps over 80°F/27°C common.AC is needed for at least six months every year. The benefits from using the LED bulbs stack.
You have the initial electricity cost savings due to the reduced wattage of the LED bulb.
Then, you have additional comfort due to the reduced heat levels. (I hate sweating while working under the heat of incandescent bulbs. My first LED bulb purchase was to replace the GU-10 halogen bulbs in kitchen track-lighting due to the heat directly on my head while working in the kitchen.)
Next, that extra heat has to be removed from the house via Air Conditioning. Every watt of heat that has to be removed has a price. AC units are rated in BTUs. A small 6000 BTU air conditioner would be roughly about 600W. Things get confusing at this point maybe someone can correct me if I’m wrong… From this page:
http://www.theunitconverter.com/btu-hour-to-watt-conversion/6000-btu-hour-to-watt.html
6000btu = 1758 watts. This seems to indicate that AC units are actually fairly efficient to me. IF I UNDERSTAND THIS CORRECTLY: A 6000 btu air conditioner is able to remove about 3W of heat per watt of power it actually uses.
So, if I have three sixty watt bulbs in that room, and replace them with LED bulbs,
I would reduce power by fifty watts each for a 150W reduction.
That would combine with an extra fifty watts in reduced AC usage, for a total of 200W savings, in the summertime.
(all with some nice estimation and rounding for easy math.)
I hope someone can correct me if I’m wrong…
There are two numbers. SEER is the ‘energy efficiency’ of the system. That is the ratio of British Thermal Units (BTU’s) cooling per watt of energy consumed. It is an awful unit because outside the USA, almost no one utilizes BTU’s any longer and consists of a hodgepodge of non-standard units. It isn’t an International Standard Unit. ISU. For the record a BTU is approximately 252 calories (which is a standard unit). A better measurement of efficiency is Coefficient of Performance. This is quite literally the ratio of energy moved to energy consumed, and SEER of 10 is roughly a coefficient of performance of 3. The best AC units these days can get close to twice that, but these units are very expensive, although it you live in climates with long AC seasons they probably have a reasonable pay back period.
In any event the rule of thumb is that each warm body in the room is about 400 BTU/Hour, and as another poster has pointed out, an incandescent light is a space heater that happens to produce some light as a fringe benefit. Consequently in environments where there is a long AC season, there is an effort is often made not to use incandescent lighting. Fluorescents are typically 80 lumens per watt, and if you don’t like Fluorescents it is probably because you have never used high CRI fluorescent lighting. It costs a lot more than the $1 per F40 bargain basement lamp. I owned a house in Phoenix that was lit primarily with GE SPX series Fluorescent lights. I used to buy them by the case at $9 per lamp, and I had to buy them from the local GE wholesaler as most lighting places didn’t want to carry them. They were too expensive. They were designed for use in commercial setting where the color rendition was very important. IIRC they had a CRI in the high 80’s.
The two main drawbacks to CFL’s are toxicity when broken and lack of dimmability. The second also affects LED lights though some are dimmable if you find the right combination of components. The first one is the major problem, and I feel that in time (perhaps this decade) the E27 type CFL’s will be regulated out of the market too. It is entirely impractical to leave a room for a half hour when a CFL breaks to allow the mercury-laden gasses time to dissipate as is recommended. In workplaces that could have serious effects- how would you like your needed ambulance or fire truck to be delayed because dispatch had a broken light bulb event? Silly?- nope, in fact OSHA requires that response. With the rapid advancement of LED lights CFL’s are already outdated and given the state of public opinion regarding environmental concerns the CFL’s have no chance for a future unless they can be economically made non-poisonous or unbreakable, and that does not seem to be in the cards.
As to the thermal properties of lighting, you must also consider the advantages of co-produced heat, In cold climes incandescent lighting is a bonus providing needed heat along with light. Electrical resistance heating is the most efficient conversion of power into heat, far surpassing heat pumps and anything flammable as 100% of the input power turns into heat. At night you turn lights on because of the darkness so Incans also help compensate for the drop in temps at night automatically, and only if that room is in use. From a ‘systems’ approach that is a hard combination to beat.
While I think we would all agree than well-informed consumers should be allowed the choice of what works best for them, the reality is that this isn’t going to happen. LED lighting is the future, perhaps the only future in lighting as LED’s can now provide almost any kind of lighting you want with more and better coming along soon.
Phil
While there are advantages of co-produced heat, you need to keep in mind that it is very expensive co-produced heat. The process of converting fuel into electricity has a thermodynamic efficiency on the order of 20%, so to produce 1kwh of heat, you need to burn 5kwh worth of fuel. It is far more efficient to simply the burn the fuel where you need it for heat, instead of in a power plant, and shipping it across hundreds of miles of wire. Let me put that into perspective for you. 100,000 BTU will require 30Kwh of electricity, at today’s rates that is about $3.00. If you want to do it burning No.2 heating oil, that is about .7 gallons, or about $1.10. If you want to produce it using natural gas (based upon a delivered cost of about $7/Mcf), the cost is about 70 cents. In short, it is a very expensive way to heat, and you are far better off using more efficient lighting, and burning fuel oil or natural gas to produce the heat. A good heat pump in mild weather can probably extract the 100,000 BTU’s for about $1 worth of electricity, as long as the temperature outside isn’t too low. However once the temperatures get below freezing, Heat Pumps perform very badly. That’s why you tend to see them only in places with very mild winters, and even then you may find they are supplemented with resistance heat. My first house in Arizona had a 5kW strip line heater that was on a timer. If the heat pump had to run more than 20 minutes at a time, the output was supplemented by the 5kW heating elements, which did ugly things to my electric bill.
s
You’re introducing costs as a factor here, and they have no direct relationship with pure efficiency. If you want to factor in costs then we have to consider the entire costs including planetary concerns, environmental impacts, loss of lives in the process of making or extracting and transporting the energy, as well as the loss of non-renewable resources. Those remain incalculable. In the end, producing heat for climate control costs something wherever you get it from and those costs will always vary. I’d simply like the option of having some of my heat come from my lighting in the winter through the easy-to-use and timely means of switching on a light during the dark hours even if it costs a bit more. I heat with electricity already anyway, and in the way I do that it is the cheapest heating option I have available to me here.
There’s another issue for me too. I’m a radio nut and only incans produce no appreciable RFI; any CFL’s or LED’s near my radio equipment causes interference with my reception thus reducing it’s usefulness to me. This is one place where so far only incan lighting is a workable solution until somebody makes better RFI-shielded LED bulbs. And I think we will have that before too long but for now we don’t. When you really get down to it, that is my sole concern regarding the future of lighting. I’m already using LED bulbs almost house-wide and I love ’em. I use one in a drop-light at work sometimes, and there’s no beating their unbreakability, safety, and total reliability in that role. I’m all for LED’s and efficiency (including costs); I just want the other possible options left for me to choose when they will work better for me and my uses.
Phil
Wait, what?
100% of the electricity turns into heat. No friction losses from motors or compressors, no incomplete combustion, no lost heat going up the chimney, no dynamic losses in blowers or ducts (or leaky ducts either).
There’s no magic that can let you exceed 100% efficiency. Factor in the atmospheric heat that a heat pump takes in along with the power it uses and it won’t be close. Don’t equate efficiency to cost or comfort- they’re different things.
Just because something sounds wrong and seems crazy doesn’t mean that it is.
Phil
That is, unless you’ve drunk the Propaganda Kool-Aid.
A lot of readers here don’t have the Science or Engineering background to be able to tell the difference between bullshit and fertilizer, and will believe whatever a charismatic presenter (PC for “Snake Oil Salesman”) tells them. It makes me sad to see how many of my fellow human beings — ostensibly the “pinnacle of Evolution” — can’t tell the difference between a Law (e.g. Thermodynamics or Momentum) and a political opinion written by some priest-class wannabe who believes s/he has the right to “rule” over us inferior “morons”.
It doesn’t take a degree- it only takes FOFY: +f+ind +o+ut +f+or +y+ourself. Only the led can be misled and I can err enough on my own without anyone else’s help thank you!
I almost signed up here as “Phaedrus” instead of “SawMaster”. That might be a more fitting screen-name :-/
Phil
Friction losses ARE heat. 100% of any energy released will become heat eventually. It is one of the laws of thermodynamics. The only question is when and where it become heat. I stand by my comment that electric heating is grossly inefficient because overall thermodynamic efficiency of the generation process is only about 20. The result is 80 of the energy consumed to produce it ends up warming the cooling pond, heating the wires, and heating the atmosphere. So while electric resistance heat converts 100% of the energy received into heat, that 100% only represents about 20% of the heat produced by a thermal powered generating process (fossil fuel or nuclear). Solar power isn’t any better. I have no information on the efficiency of wind turbines or hydroelectric.
Let me know when you find someone successfully selling a furnace that is only converts 20% of the fuel into useful heat (and 80% goes up the chimney). You can now buy natural gas powered heating plants that convert upwards of 90% of the energy in Natural gas into useful heat.
When you factor in the generating efficiency for electricity you’re affecting heat pumps (which run on electricity) and your gas or oil furnace too (which need electricity for control circuits, pumps, igniters, thermostats and blowers). None of that is calculated into the advertised efficiency ratings, plus those numbers are taken directly at the air handler or heat unit’s output- once you send the output down the ducts some of that efficiency is lost. Also those numbers usually don’t include the blower/filter system with it’s inherent losses but rather are inferred from what their engineers see the as optimum airflow rate.
As to your friction into heat thoughts, that only counts when it is in the ducted airflow of the unit. With a heat pump, the compressor and it’s motor are outdoors and that co-generated heat is wasted- it does not enter the interior. It stays outside.
Yes, today’s heat systems are far more efficient than those of just 20 years ago. Great advances have been made in that area. But the one type which has not changed is electric radiant heating because there is really no way to improve it- you can’t improve on 100% and that is why it is the same.
I’m not going to argue the point further (especially since it’s derailing someone else’s thread now). Just find out for yourself- the details, specs, and data are available online for the whole schmeel. Compare apples to apples and you’ll discover what I did. I had to be convinced too 
Phil
Most of the “heat” from an incandescent lamp is emitted as infrared light. Incandescent lamps are actually very efficient at producing light, around 80% or something like that; just most of the light is invisible.