# Different types of dimmers



## sparkiez (Aug 1, 2015)

Can anyone suggest an authoritative site / text / resource or want to give information on the various different types of lighting dimmers and how they function? I know that is somewhat of a broad subject, however we were discussing it at work and want some details into the functionality of the various types of dimmers.


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## HackWork (Oct 2, 2009)

In..


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## splatz (May 23, 2015)

It's a good question, I have turned up some good whitepapers etc., here is one:


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## MikeFL (Apr 16, 2016)

It will help us to help you if you tell us at least what kind of lights you're talking about.

In your office?

Parking lot?

MLB Stadium?

I ask because we make dimmers but there's plenty of ways to do each.


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## frenchelectrican (Mar 15, 2007)

sparkiez said:


> Can anyone suggest an authoritative site / text / resource or want to give information on the various different types of lighting dimmers and how they function? I know that is somewhat of a broad subject, however we were discussing it at work and want some details into the functionality of the various types of dimmers.


It will be nice if you are little more specific on what are you try to discuss the type of dimming system it is. 

there is a lot of different verison out there so it will help us a bit if you narrow it down some.


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## sparkiez (Aug 1, 2015)

Thanks for the responses so far. I understand the complaint about me being vague. This is very much an academic question. I don't have a particular type of dimmer I'm interested in. I'm interested in a bit more detail in how dimmers for different types of lighting function. Here are some questions that pop into my mind:

Can an incandecent lamp just be dimmed by reducing voltage (resistive dimmer type) I think this would be very inefficient.


Are LED's dimmed by adjusting their frequency / peaks / both?

Why can't you just reduce voltage to a driver in order to dim an LED?


What about metal halide or high-pressure sodium lamps? Can they be dimmed? Aren't they just incandescent lamps with a different gas, and elements of a different geometry?


I completely understand an annoying vague question, so I appreciate the help thus far. I also have not had a chance to read that white paper yet. I'm getting ready for inspections this week, so I'll get it done this weekend. I try not to spend all of my off time looking at electrical stuff.


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## 460 Delta (May 9, 2018)

I'll throw an old one at you, a dc saturable reactor.


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## Kevin (Feb 14, 2017)

0-10 volt dimmers
Electronic low voltage dimmers
Triac dimmers

Oh we're not listing dimmers? Google has lots of info on how dimmers work. There are certain dimmers for certain applications.

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## MikeFL (Apr 16, 2016)

Just on the 0-10V DC dimmers there is 0-10V, 10-0V & 1-10V dimming protocols. Common on LED lights.

There's also PWM (pulse width modulation) protocol. Another LED protocol. Also used for motor speed control, etc.

There's the old school rheostat which limits the current variably by changing the resistance. This works well with incandescent.

We have 3 major league baseball stadiums in our county. They use a company out of Iowa who controls the lighting. Throughout the day as the sun moves and the weather changes they are continuously changing the dimming as well as orientation of each fixture to produce the best television broadcast they can. Each stadium is effectively a large scale television studio. You could look them up if you want to know more about it.

Wal-Mart has a light sensor in a domed skylight in every store. They switch outdoor lighting on and off as a function of the sensor output. At a given light level they turn on the corners of the parking lot and signage. Other light level triggers the parking lot perimeter and landscape lighting. Yet another level triggers the parking lot infield. They also dim inside lights according to the outside ambient light level.

One of the oldest means of "dimming" involves having multiple fixtures on a pole and having multiple switch legs. For the most light, turn all the lights on. For less light turn some of the lights off.

To dim a hurricane lamp you rotate a knob which causes the wick to travel vertically. 

Not sure what your purpose of gathering this information is or who your audience is. Maybe give us that info and we can give you more info. Are you teaching a class? Does your boss want to know what options are available for a given application?



sparkiez said:


> Thanks for the responses ...
> 
> 1. Can an incandecent lamp just be dimmed by reducing voltage (resistive dimmer type) I think this would be very inefficient.
> 
> ...


1. We do that with the rheostat which limits the current by changing the resistance as you rotate the knob. As easy to understand as Ohm's Law.

2. There are many ways. Texas Instruments has a good paper discussing some of the means to do such. https://e2e.ti.com/blogs_/b/powerho...ghtness-adjustment-high-frequency-pwm-dimming

3. Are you asking if we could input 90V to a driver instead of 120V and dim the light that way? Something spec'd @ 120V needs to be tested to 90V to account for variations in voltage levels from the power source.

4. Not quite. 

Incandescent has N2 gas to prevent combustion of the filament. To have fire we need 3 conditions present: heat, fuel, oxygen. By evacuating O2 the incandescent bulb manufacturer allows the filament to glow but never reach combustion. To do a little test, break the glass off an incandescent and power it up to see how long it lasts (in a safe environment, of course).

HID contains a gas which glows when energized. That gas gets consumed, very slowly, over time.


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## 3DDesign (Oct 25, 2014)

I prefer Lutron; Adriana, Diva & Caseta.


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## sparkiez (Aug 1, 2015)

Thank you for the awesome information. I'll be sitting down this weekend (tomorrow morning with my coffee) and reading through those white papers and taking some notes. I'll bring questions I have back here. The purpose of this thread is primarily for my own curiosity. It occurred to me the other day that despite having installed a ton of different types of lighting, I have never really studied the topic much.



MikeFL said:


> 2. There are many ways. Texas Instruments has a good paper discussing some of the means to do such. https://e2e.ti.com/blogs_/b/powerho...ghtness-adjustment-high-frequency-pwm-dimming
> 
> 3. Are you asking if we could input 90V to a driver instead of 120V and dim the light that way? Something spec'd @ 120V needs to be tested to 90V to account for variations in voltage levels from the power source.
> 
> HID contains a gas which glows when energized. That gas gets consumed, very slowly, over time.


Thanks for the link to the paper and the detailed response.

3. Yes, was looking at adjusting the voltage going to the driver. Now, I was under the impression that LED's are frequency based, and the other colors of the light emitted were based on the band-gap of that particular material, and thus the quantity of light emitted is tied to the frequency. This is also where I see PWM on the driver output being an obvious way to dim the light.

I have some other ideas on how this works, but I would rather read through these papers and see if my questions are answered here.

Now, touching on 0-10V (or 10-0V) dimming, it seems to me that there is just that span, that is proportional to the frequency output of the driver. I've seen this in a system where there was one driver for multiple fixtures, or where there are multiple fixtures, and I can only assume that you parallel the (+) and (-) to the fixtures, and the dimmer is a variable resistance.

Now, for incandescent dimming, as you mentioned one of the older ways was to just vary a resistance to act as a current limiter. Wouldn't this setup just act as a voltage divider and dissipate power via heat in the variable resistance (and be pretty inefficient) ?


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## sparkiez (Aug 1, 2015)

3DDesign said:


> I prefer Lutron; Adriana, Diva & Caseta.



Those Caseta wireless switches are the bomb.


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## paulengr (Oct 8, 2017)

Very, very different technologies.

Incandescent lamps are dimmed by varying RMS voltage. You can use a rheostat (resistor) but at 50% losses at 50% power, efficiency is awful. There are variacs which are variable transformers. Not great efficiency but huge size for what they do. Real lamp dimmer for incandescent simply use an SCR circuit to chop the wave so that it varies the RMS voltage seen by the lamp very efficiently. With an SCR it blocks voltage until you apply a pulse to the gate to turn it on. It stays on until the AC current goes through zero which it does 120 times per second. In an incandescent lamp we have a solid filament which is basically a resistor. We are heating it so hot that it glows. Everything glows if it is hot enough. But also as temperatures go up so do chemical reactions like oxidation. If the smallest amount of oxygen is around it fails in seconds. The filament will slowly deform when it is hot (called creep). But the big problem and this goes for everything that has a glass bulb is that it is impossible to totally seal the glass/metal connection against leaks. This controls how long a bulb lasts. About 20 years ago inductive lamps hit the market that used induction to get power to the lamp. They easily ran 100,000-200,000 hours. They never caught on for various reasons so they went off the market.

Nothing is consumed in HID as such either. Again leaks at the glass/metal joint ultimately determine life. HID lighting includes metal halide, sodium vapor, mercury, fluorescent, neon, and for nostalgia lime lights. All of these are arc discharge lamps whether sodium or mercury or some other vapor. During starting with most of them the mercury or sodium is vaporized first. Then it creates a controlled arc. When an arc passes through it blows the electrons off the molecules. As the energized electrons return back to the molecules they dump the excess energy as light. With neon and sodium that’s the whole process. With mercury much of it is UV. This makes mercury lights purple. The right mix of halogen gas converts UV down to visible light and the light is more efficient. That’s the principle of the halogen (solid filament) and metal halide (mercury vapor) lamps. Fluorescent bulbs are also mercury lamps except it uses a phosphorescent paint to convert UV to visible light. The arc has a fixed minimum required voltage and they burn out with excessive voltage. The electronics keeps the current from running away. Obviously we can’t just increase or decrease voltage with arc discharging or it is very limited. Dimming means cutting the arcing time. This requires a sophisticated circuit that turns both on and off at the right time with a transistor. There are a bunch of ways these lamps “age” but in addition to leaking glass seals mercury and sodium vapor tends to accumulate in places other than the “boiler” so it gets lost stuck on the glass where it never boils and eventually the lamp fails.

Finally LEDs are actually DC diodes. There is a voltage drop in all diodes. When an electron hits the drop it loses energy. The energy it dumps is a specific frequency/wavelength/color. The voltage drop is the band gap. It is determined in manufacturing and cannot change. White LEDs (“all colors”) are sort of fluorescent technology reborn. They are blue LEDs with a white phosphorescent coating. Power diodes including LEDs including have a nasty property where the resistance decreases as they heat up so they can go into thermal runaway where as temperature goes up resistance drops which increases current which increases temperature which feeds on itself. So rather than voltage control the driver circuits normally maintain constant current to prevent damage from overheating. So varying the input voltage is going to mostly be counteracted by the driver circuit which is throttling current even as voltage fluctuates. LEDs turn on and off almost instantly. They can be dimmed by changing current but it’s not very linear. So pulsing them and varying pulse width is the way to go. There are two ways that they get a pulse command. Many commercial lights like 4 foot troffers take an external 0-10 VDC input. Vary the signal to vary output and in this case a simple potentiometer is the way it’s done. The electronics runs the LED at high frequency just so that it does not visibly flicker, say 100-200 Hz, and converts 0-10 V into a 0-100% pulse width signal. Most commercial office fixtures work this way. The option is inexpensive. The second way is for incandescent retrofits. Some drivers in Edison socket style lamps detect the chopped wave from a standard dimmer and pulse the LED to make it dim using the lamp dimmer pulses as a control signal. These are sold as so called dimmable LED lamps. So you can use your lamp dimmer and it “works”. They do work so-so but from my experience they don’t last very long. Poor driver quality.



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## MikeFL (Apr 16, 2016)

And the 0-10 is a control signal only. It does not drive the load.


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## sparkiez (Aug 1, 2015)

MikeFL said:


> And the 0-10 is a control signal only. It does not drive the load.



Right. That span (0 - 10)V is proportional to some frequency span. More or less light is emitted by varying the frequency. Just wanted to confirm that. Constant power to the driver and your switch varies a 0-10V signal.


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## sparkiez (Aug 1, 2015)

Just read paul's post as well. It seems that a lot of my conceptions about dimming are pretty spot-on. What brought this up was that the guys installed some cans that took triac, EVL or 0-10V dimmers. I was asked to figure out what needed to happen, but I couldn't give a definitive answer.

I'm still not sure how varying the voltage to the input of a driver would dim the driver unless the driver can just handle having less power delivered. I don't have the specific part number handy.


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## MikeFL (Apr 16, 2016)

Probably an op amp (talking to an op amp).
Output relative to input.


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## sparkiez (Aug 1, 2015)

MikeFL said:


> Probably an op amp (talking to an op amp).
> Output relative to input.



This won't be technically correct, but I don't think we need that for that conversation:

Driver gets power. Has some minimum voltage threshold to run.
Driver "senses" that voltage
Driver varies the output frequency based on the input voltage


You don't need specific values, such as 0-10, because as you said, with multiple op-amps it becomes a relative signal and as long as you have enough RMS power to keep the power electronics happy the driver functions as intended.


EDIT: Also, post 420


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## paulengr (Oct 8, 2017)

sparkiez said:


> This won't be technically correct, but I don't think we need that for that conversation:
> 
> Driver gets power. Has some minimum voltage threshold to run.
> Driver "senses" that voltage
> ...




It’s not frequency. It’s pulse width. So at say the frequency is 10 milliseconds or 100 Hz so it avoids visible flicker. 10% means on 1 millisecond, off 9 milliseconds. On 90% means on 9 milliseconds, off 1. If it’s on 50% and off 50% even if we go from 10 to 1000 Hz it’s still 50% output, All dimmers work on pulse width.

The “dimmable” drivers output a constant current or voltage during the time the pulse is on even though voltage is fluctuating so the current is jumping to compensate as voltage sags.


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## MikeFL (Apr 16, 2016)

It only takes about 30Hz to fake out human eyes.
Video is 30 frames per second.


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## sparkiez (Aug 1, 2015)

Thanks for all the information on this thread. It was a lot of help clarifying some of the underlying technology when working with dimmers. I just have one more question about these things.

So, I've noticed at times, that LED lamps will just barely be on. I've also seen it happen with CFL's if on the same circuit with LED's. It is also important to note that it was on switches that do not need a neutral. Is this due to voltage bleed-through on the switch?


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## Jarp Habib (May 18, 2014)

MikeFL said:


> It only takes about 30Hz to fake out human eyes.
> Video is 30 frames per second.


Many people's eyes.


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## Mack Fisher (May 27, 2019)

I have had the most problems with dimmers in rental units, the ceiling fans with lamp kits and the single gang dimmer for motor speed and lamp intensity. The renter goes out and buys a new (non-dimmable) LED or compact fluorescent and burns out the dimmer. My fix is to replace the damn thing with a conventional switch I make the same amount for the service call and a landlord gets a lower bill. I guess I’m just a evil person let him squint.


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