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LED lights and dimmer switches

Matty1973

Critical Thinker
M
Joined
Mar 27, 2005
Messages
253
The "Banning Incandescent Light Bulbs" thread has become quite large and covers quite a lot of different areas but one question that has been raised a couple of times and not been answered as far as I can see relates to dimmer switches with LED's. If the mods feel this is best answered as part of the main thread then please merge it but may be you could wait a few days for it to be answered so I can clearly see the opinion before it gets lost in that thread.

I have a dimmer switch in my living room with halogen bulbs - these use 50W so I thought I would try LEDs (2W). I hear from many sources that these can not be used with dimmer switches but the reason behind is not so forth coming.

My experience is that three of the bulbs seem to work fine and one comes on at half brightness. This seems to be the case regardless whether the dimmer switch is set at full/half/less.

So my main question is whether it is dangerous to use dimmers with LEDs?

I assume not since it is only 2W. So if it is not dangerous does it cause damage to the LED or is there any other side effect I should worry about? I thought there was a chance the LEDs would not function at all, but in general they seem fine - the one at half brightness may be because I bought relatively cheap ones from ebay.
 
The main reason is that the dimmer switches generally do phase blanking. The voltage of standard AC crosses the zero voltage line 120 times per second. Phase blanking stops the voltage at zero and holds it there for a variable amount of time (depending on the setting) before letting it rise to where it should be . The amount of energy sent to the bulb is lowered. Incandescents don't mind this; their thermal energy fills the gaps. LEDs operate on DC, not AC, so the whole approach is wrong for them.
 
Matty1973 said:
The "Banning Incandescent Light Bulbs" thread has become quite large and covers quite a lot of different areas but one question that has been raised a couple of times and not been answered as far as I can see relates to dimmer switches with LED's. If the mods feel this is best answered as part of the main thread then please merge it but may be you could wait a few days for it to be answered so I can clearly see the opinion before it gets lost in that thread.

I have a dimmer switch in my living room with halogen bulbs - these use 50W so I thought I would try LEDs (2W). I hear from many sources that these can not be used with dimmer switches but the reason behind is not so forth coming.

My experience is that three of the bulbs seem to work fine and one comes on at half brightness. This seems to be the case regardless whether the dimmer switch is set at full/half/less.

So my main question is whether it is dangerous to use dimmers with LEDs?

I assume not since it is only 2W. So if it is not dangerous does it cause damage to the LED or is there any other side effect I should worry about? I thought there was a chance the LEDs would not function at all, but in general they seem fine - the one at half brightness may be because I bought relatively cheap ones from ebay.
Click to expand...

Dangerous? I ruined a $30 LED 40 watt light because of this curiosity. It died pretty quickly. This LED lamp was not rated for dimmers. I can't see how it would create a fire given the hefty aluminum base these things have.What I do because of the high cost of the LED units, if that circuit has a dimmer, is take it out and put a standard switch in.

But there are some reports of fires with CFL. Those have cheap plastic bases that holds the voltage conversion circuit, and they need to create a way higher voltage. LED only needs about 6 volts.

For any supposedly rated "dimmable" and this means LED, halogen and the CFL - do not expect either the same range of dimming or the changes in color which occur with incadescent. CFL seems to go from 40% to 100% for example, while incadescent goes from 1% to 100%.

Also, note that there are some special dimmers for use with CFL. You replace the bulb with a CFL, then you replace the old dimmer with a new one.

Finally, there are actually some old dimmers around that are just a big resister with a sliding contact. They should be basically thrown away.
 
LED lights can be dimmed, by varying the current flowing through them. I am not aware of any commercial lighting product that works in that way.
As was pointed out previously most light dimmers work by adjusting the duty cycle of the AC waveform presented to the device. As the mains (US) of 120v has to be stepped down to the low voltage needed for the LED it is usual to have a constant current source built into the interface.
As you turn down the dimmer, usually by changing the phase angle to a thyristor, the LED power converter copes just fine until there is insufficient energy to maintain operation. The effect will thus be: full,full,full,full,dim,off,off,off.
The angular spread of the full/dim/off transition is probably too fine for most dimmer switches.
There is not a safety issue with this, by the way.
What is needed is a circuit that converts the average incoming supply to a variable current source for the LED. That is relatively trivial to implement, but I have not seen any impetus to offer that capability.
I have an LED ring illumination device for one of my microscopes, and I built a variable current source for it running off 12v DC. I can adjust the brightness to a fine level.

V.
 
I'm glad that it appears there is no danger in what I am doing.

I am not to worried about being able to dim the LEDs - more concerned whether I need to go to the trouble of having to replace the dimmer with a on/off switch (the wires are quite short so it was quite difficult installing the dimmer - having to change it again is something I would rather avoid if possible - especially if in a year or two I would need to reinstall the dimmer once dimmer friendly LEDs becomes cost effective)

Verde said:
As you turn down the dimmer, usually by changing the phase angle to a thyristor, the LED power converter copes just fine until there is insufficient energy to maintain operation. The effect will thus be: full,full,full,full,dim,off,off,off.
The angular spread of the full/dim/off transition is probably too fine for most dimmer switches.
V.
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This interests me. I wasn't sure if there was a dim period between the full and off. Since one LED is currently dim I was thinking it was defective rather than to be expected when used with a dimmer. Although why it is only one bulb I'm not sure.

To put it all in perspective the LEDs I bought were $15 for 4 including shipping so quite cheap really. They are warm/day light and 30 LEDs per bulb.
 
Matty1973 said:
This interests me. I wasn't sure if there was a dim period between the full and off. Since one LED is currently dim I was thinking it was defective rather than to be expected when used with a dimmer. Although why it is only one bulb I'm not sure.
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The dim part is like falling off a cliff; you may be able to land half-way down but don't count on it being the same each time.

It sounds like you had a duff bulb. Probably the regulators were split across the LED banks, and one was defective. We are still a long ways from having high power individual LEDs, so pretty much all commercial bulbs use multiple devices, and the associated current sources add to the complexity.

I have most of my external lights replaced with LED units. They are all in fixtures that need wrenches and screwdrivers to remove the ornamental covers, so it was more a matter of convenience rather than cost. I used to have to replace the incandescent bulbs every few months; the LEDs have lasted for several years.

V.
 
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bikerdruid said:
has household LED lighting gotten practical yet?
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Yes. I've replaced all my old CFLs with LEDs and I am extremely happy with them. I bought them at the local Albert Heijn (a Dutch supermarket chain) for 25 euro a pop. Considering that they'll last 25 years instead of the half year or so that 50 cent incandescents last, that makes them cheaper even if you don't consider they use 10 times less energy. The quality and quantity of the light seems far better than my old CFLs. I think it is gorgeous. I can't really compare them to incandescent lights because I haven't used those in a long long time. Their light probably isn't exactly the same, but who cares about that anyway... Incandescent bulbs didn't produce the exact same light as the candles they were meant to replace and nobody cared. My LED bulbs are supposedly dimmeable too, I just don't care about such nonsense.
 
Verde said:
We are still a long ways from having high power individual LEDs, so pretty much all commercial bulbs use multiple devices, and the associated current sources add to the complexity.
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Hmmm. . .is anyone working on a dimmable LED bulb that dims by turning off individual LEDs? I realize this wouldn't use a regular dimmer switch, but would require that stuff built into the bulb and/or fixture. However, I think the future of home lighting will involve a lot more remote control anyway. . .


Anyone know if what I'm saying is at all feasible?

Home wiring especially in older homes is always a little bit of a history lesson. Before I re-wired my entire c. 120 yr old house, I had some bits of grounded romex roughly vintage mid-'70s, some ungrounded encased wiring, and some very old knob and tube wiring. (For that matter, when I went to install light fixtures in two rooms where there hadn't been any ceiling fixtures, I found gas lines running to where very old lights used to be.)
 
bikerdruid said:
has household LED lighting gotten practical yet?
a few years ago, there was very limited choice and the price was high.
can anyone link to a selection of lights for home use?
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Selection has gotten considerably better in the last year. For example, this is what Lowes now carries:
http://www.lowes.com/pl_LED+Light+Bulbs_4294801193_4294937087_

I recently bought a few of the UtiliTech 40-watt equivalents (~$10 each). They seem to put out about as much light as the 60-watt equivalent CFL's. But they aren't perfect. The color is on the cool side (I'd prefer a warmer light), and they also throw light primarily in one hemisphere. I mounted three of them in a ceiling fan light pointed downward, and that actually didn't work so well because it left the ceiling depressingly dark, so now I only have two mounted there and have a third CFL to keep the ceiling illuminated. There are higher-power LED's that have a much better angular spread, but they cost a lot more ($30+).

If you're still running with incandescents, it's not a bad time to try out a few LED's and seeing if they work for you. But while even a $40 LED bulb can pay for itself over a lifetime compared to an incandescent, if they drop to $20 next year, you won't have saved enough money in the mean time to justify the premium. So it's still early to switch completely unless the cheaper LED's satisfy you.

If you're using CFL's and are satisfied with them, I'd say the price is definitely too high to justify switching out working bulbs, though you might consider replacing dead bulbs.
 
An online retail company with a name similar to "ThinGreek" (but with an extra k and no r)* sells a $40.00 5-watt LED bulb that has dimming and color setting via a remote control. Probably not as convenient as using a wall dimmer for room lighting (especially where one wall dimmer would control several fixtures), but it might fill a need.

Respectfully,
Myriad

*Actual name concealed to conform to the new Rule 6.
 
bikerdruid said:
has household LED lighting gotten practical yet?
a few years ago, there was very limited choice and the price was high.
can anyone link to a selection of lights for home use?
Click to expand...

Very reasonable. Check out a deal extreme, it's a Chinese supplier with free shipping and just about anything you want for next to nothing. There's hundreds, maybe thousands of LED products, anywhere from single LED turn signal lights to multi-die LED flood lights.

If you're inclined to tinkering it's amazing what you can do with LED's. I purchased a 12V IR remote control unit for $6. It's designed for use with these RGB LED strips but works with any 12V LED light. It has a multi-function strobe, flash, fade and dimmer. With that and a little conductive paint I've made some remote controlled poster/painting lights that are virtually invisible.

The CREE LED's, the ones they use in flashlights, are extremely efficient and extremely bright, a 5mmx5mm LED puts out 1000 lumen at 3000ma and is rated for some 100 000 hours.

I'm speculating, but I can imagine in the not too near future AC lighting will be a thing of the past. I can see a separate 12V or 3V DC system emerging dedicated to lighting and perhaps computers and peripherals. It's safer and requires a lot less copper wiring.
 
JoeTheJuggler said:
Hmmm. . .is anyone working on a dimmable LED bulb that dims by turning off individual LEDs? I realize this wouldn't use a regular dimmer switch, but would require that stuff built into the bulb and/or fixture. However, I think the future of home lighting will involve a lot more remote control anyway. . .


Anyone know if what I'm saying is at all feasible?
Click to expand...

It's actually rather easy to dim individual LED bulbs, and to do so in a continuous and well-controlled manner. The problem is that you really want to do that with separate electronic controls while keeping the line voltage unchanged, and you can't do that through an Edison socket with only two connections. There are ways around that, but they would be more expensive. For example, you could simply put a radio receiver in each bulb, and a radio controller as either a remote or possibly built into the wall. In fact, such a thing already exists:
http://www.amazon.com/Multi-Color-E...ZSEG/ref=sr_1_1?ie=UTF8&qid=1306712365&sr=8-1
It's a multi-color LED bulb with a remote control to adjust color AND brightness, as well as a few effects like strobe. I don't know what the cost premium would be for adding this to standard LED bulbs, though, so that might be a problem.
 
Myriad said:
An online retail company with a name similar to "ThinGreek" (but with an extra k and no r)* sells a $40.00 5-watt LED bulb that has dimming and color setting via a remote control. Probably not as convenient as using a wall dimmer for room lighting (especially where one wall dimmer would control several fixtures), but it might fill a need.

Respectfully,
Myriad

*Actual name concealed to conform to the new Rule 6.
Click to expand...

Actually I think the remote I'm speaking of works with the light you're talking about and you can get them on eBay for $7 now. (they have about 40 RGB LED's in them?)
 
3bodyproblem said:
I'm speculating, but I can imagine in the not too near future AC lighting will be a thing of the past. I can see a separate 12V or 3V DC system emerging dedicated to lighting and perhaps computers and peripherals. It's safer and requires a lot less copper wiring.
Click to expand...

It's safer because you don't need to worry as much about shorts, but I don't think you're right about it requiring less copper. In fact, since many appliances would still run off of 120V AC for the foreseeable future (like vacuum cleaners, microwaves, power tools, etc), it seems like you'd need MORE copper wiring to run a parallel low-voltage system. Furthermore, the gauge of wire needed is determined by the current, not the power, and dropping the voltage will increase the current. I'd like to see a low-voltage home standard happen, and it might be worthwhile, but I doubt you're going to save on copper by doing so.
 
Ziggurat said:
It's safer because you don't need to worry as much about shorts, but I don't think you're right about it requiring less copper. In fact, since many appliances would still run off of 120V AC for the foreseeable future (like vacuum cleaners, microwaves, power tools, etc), it seems like you'd need MORE copper wiring to run a parallel low-voltage system. Furthermore, the gauge of wire needed is determined by the current, not the power, and dropping the voltage will increase the current. I'd like to see a low-voltage home standard happen, and it might be worthwhile, but I doubt you're going to save on copper by doing so.
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I'm just thinking you don't need to run AC in the ceiling.

Like all the fluorescent lights in the ceiling, replaced with multi-die CREE's running off tiny 2 wire DC? You'd never have to change them.

That can all be done with 2 wire 16 gauge probably.

Just thinking outside the box here.
 
JoeTheJuggler said:
How do they work for you? How do you like them?
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I bought the cheapest ones (30 LEDs instead of 60 LEDs) and they are not as bright as the 50W halogens they replaced but they are good enough to light the room. The colour of light seems fine - not harsh as I feared.

The main reason I bought them was the halogens were over heating and burning out on a very regular basis. So far the LEDs have not burnt out, although as I mentioned before one of the four bulbs I purchased only comes on at half brightness so I will see if the company will replace it. I plan to try a packet of the 60 LEDs too.

Overall I am impressed by them.
 
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