If you dim light does it consume less electricity?

[DNYANDEEP]

If you dim domestic lights using a standard dimmer switch, do you actually consume less electricity?

[AbydosOne]

7 minutes ago, DNYANDEEP said:

If you dim domestic lights using a standard dimmer switch, do you actually consume less electricity?

Yes.

[Eigenvektor]

Dimming works by either reducing voltage (DC), by rapidly turning it on/off (PWM e.g. LEDs) or in the case of AC by reducing the amount of AC cycle that reaches the light.

 

This means that either Watt = Voltage x Amps is reduced or the amount of time the light is actually on is reduced. And since the electricity you pay for is Watt x Hours (i.e. Wh) reducing either Watts or Hours will reduce the amount you have to pay.

[AbydosOne]

Just now, htimsenyawed said:

Interesting. I like my IoT bulbs because I can dim them without needing to fish new Romex with that 4th wire. Do they function the same?

Fourth wire?

[LAwLz]

It depends on the dimmer.

 

Old dimmers worked by being a variable resistor (a rotary rheostat). Those dimmers and light bulb combos will always consume the same amount of power because the dimmer dims the light by using up more or less power themselves (by being more or less resistive). In other words, if you dimmed the light, the dimmer itself would get hotter because that energy that didn't get sent to the light bulb was turned into heat instead.

If you had a 60-watt light bulb and dimmed it down to 50%, the dimmer would use 30 watts of power and produce 30 watts of heat.

 

Modern dimmers work by essentially turning the circuit on and off very rapidly. As a result, it ends up consuming less energy.

 

 

Unless you happen to have a very old dimmer, dimming your light do end up consuming less power.

[Eigenvektor]

1 hour ago, htimsenyawed said:

Interesting. I like my IoT bulbs because I can dim them without needing to fish new Romex with that 4th wire. Do they function the same?

An LED can be dimmed by either rapidly turning it on and off or by reducing current, both of which doesn't need more than power and ground. You're probably thinking of PWM fans, which have power, ground, tach and a PWM wire.

[Kid.Lazer]

@htimsenyawed

Even though the dimmer has 4 wires, doesn't mean you send all 4 to the device that is being dimmed. The Ground and Neutral wires will all tie together. The Hot (from your circuit breaker) will connect to the black wire on the dimmer, then the remaining wire(s) on the dimmer (brown, red, or black depending on brand/model) connects to Hot (black) on the device you're dimming. (all based on NA wiring colors)

Spoiler

 

[Eigenvektor]

8 minutes ago, htimsenyawed said:

I have no idea what a PWM fan is. Can you explain?

A fan whose speed is controlled by pulse width modulation. You can either control a fan's speed by changing its voltage or by using PWM (i.e. voltage remains constant). Those have four cables, two that supply power, one that is used to read the fan's current speed and one that is used to supply the pulses that turn it on/off.

 

A motor needs a certain amount of power to get going, so voltage controlled fans typically can't go slower than 40% of their max speed before the motor can no longer overcome the fan's inertia and stops. It might get going if you give it a push, but otherwise it'll be stuck in this weird state where it twitches a little but doesn't start to rotate.

 

A PWM fan, like a PWM controlled LED, rapidly turns power on and off, effectively giving the fan a push at full power every now and then. Depending on how many pushes you give it vs how long power is turned off, you can vary its speed in a much wider range than a voltage controlled fan.

 

Similarly varying voltage of an LED might have a negative effect on its color temperature. PWM on the other hand can result in visible flicker if the frequency of pulses aren't fast enough (https://www.waveformlighting.com/film-photography/an-introduction-to-flicker-free-led-strip-dimming). If you've ever used an old CRT at 60 Hz or below you know what I mean.

[Kid.Lazer]

1 hour ago, htimsenyawed said:

I'm not much an electrician, my buddy was a commercial electrician though. So you're saying that even with a regular 12/3 Romex I can use those switches by tying the appropiate wires together?

Yep.  Typically you only need 4 conductors in a residential 120v application if you A: are installing 3-way switches (2 or more switches controlling the same circuit) or B: want to control separate features of a single device (like a ceiling fan and light having separate switches.)

[BrandonLatzig]

8 hours ago, LAwLz said:

Modern dimmers work by essentially turning the circuit on and off very rapidly. As a result, it ends up consuming less energy.

I wonder then how one of my dimmers work, it has multiple steps, and I don't think that can be obtained by just turning it off and on again rapidly

[Eigenvektor]

4 hours ago, BrandonLatzig said:

I wonder then how one of my dimmers work, it has multiple steps, and I don't think that can be obtained by just turning it off and on again rapidly

Yes, it can. But as others and I have pointed out along the thread, there are multiple ways to dim. Could be using resistive dimming and switching between concrete resistors. Could be switching between concrete voltages. Could be using PWM and switching between specific profiles.

 

The way you dim with PWM is by rapidly turning it on and off and varying the relative length off the on/off cycles. If both are the same length, then you're at 50% brightness. If it is off 2/3 of the time and on 1/3 of the time you're at 33.3% brightness. Off 3/4, on 1/4 and you're at 25%. Off 1/4, on 3/4 = 75% and so on.

[Mark Kaine]

On 12/20/2023 at 5:01 PM, htimsenyawed said:

 

Every dimmer switch we sold at the hardware store I worked at (local, not Lowe's or anything) required white, black, red and green (ground). Nothing in my house has the red, so I don't have any dimmer switches.

 

Edit: I found this example which requires a fifth wire (brown) as well.

not true,  we have 3 wires here mostly, 4 max, and dimmers work just fine. 

[Mark Kaine]

44 minutes ago, htimsenyawed said:

I’m not sure which part of that statement was untrue, aside from my misunderstanding of electricity.

im just saying you don't need more than 3 wires? idk how it works,  i just know it does work.

 

 

(also no "ground" here,  and no issues... another myth, you don't need ground,  cause everything is already grounded to earth (the planet!) typically! )

 

¯\_(ツ)_/¯ 

 

 

ps: additional interesting information: electricity also doesn't "flow" thru wires at all - another bs myth kids learn in school >.<

 

 

 

 

[Mark Kaine]

1 minute ago, htimsenyawed said:

 

I'm having a hard time believing this one because of the use of ground rods when doing electrical installations. I know that when I worked at the hardware/lumber supply store, electricians would come in and usually get 3 ground rods for the electrical service.

eh, you need *3* wires,  yes. but you don't need 4.

 

ground/earth might just be a language issue... very confusing because its the opposite in us vs eu, for example. 

[Mark Kaine]

2 minutes ago, htimsenyawed said:

 

From my understanding of the ground rods, they're drove into the ground/earth and are tied into the electrical system of a house for the grounding of the system. Here is a good article about them that gave me the basis of my knowledge of them.

yes. but - you  don't need that - provided that's the thing you need for a "ups" to work.

 

in other words, a ups doesn't work here (because i only have 2 or 3?) wires, yet there's simply no issue,  the fuses in the house work just fine.

 

my electrician literally said "these lines have no ground"  (i think its what Americans call "earth" confusingly...) 

[Mark Kaine]

16 minutes ago, htimsenyawed said:

 

No, we call them ground as well. And the ground rods doesn't appear to be what you need for just a dimmer or a UPS, but to protect your electrical system from grid surges or electrical storms.

well, as said, i don't have the thing you need for a ups. however dimmers work just fine as said (i had 1 in this room for years) 

 

blackouts, thunderstorms, chinese faulty usb cables... pc is still going strong!  (although it would probably fry with a direct lightning strike anyways lol) 

 

as said, it also does trigger the fuses - which is the important part ("tested" with faulty Chinese power supply)

 

 

^ thats not to say i don't like Chinese products,  my favorite  brands are Chinese, like segotep, superflower, zeaginal, colorful... all top tier stuff!