Dimmer switches are a somewhat common form of light switch which allows you to control the light beyond on/off by instead giving you the option to put it at a brightness somewhere in between.
Seeing as dimmer switches are able to make the light produce a dimmer light than its 100% capacity, that means it should theoretically save energy, right?
The energy-saving capabilities of a dimmer switch depend on multiple factors such as the type of light bulb being dimmed and sunlight compensation, but in general dimmer switches are expected to save around 5-20% of the energy used on lighting with 14% being standard for commercial buildings.
While this is the general answer there are a lot of nuances that go into how much energy a dimmer switch can actually save you when used optimally.
- 1 How Much Energy Do Dimmer Switches Save?
- 2 How Dimmer Switches Work
- 3 Factors That Determine The Effectiveness Of Dimmer Switches
- 4 Summary
How Much Energy Do Dimmer Switches Save?
While the expected energy savings from using a dimmer switch are normally anywhere between 5-20% there is more to it than just that. The amount you save is dependent on a lot of different factors.
The Relationship Between Light Output And Energy Consumption
The first thing to understand regarding dimming and energy savings is the relationship between a bulb’s light output and the energy it consumes. In order to make sense of this we first need to differentiate light bulbs and put them in two different groups. The different groups are:
- Resistive light bulbs
- Electronic light bulbs
This simply refers to the way the bulbs function as electrical loads. Resistive electric loads are electrically “pure” in that they function by having an increased electrical resistance, which helps them produce heat in this instance.
This group includes incandescent bulbs and halogen bulbs, where the resistive load is a tungsten filament which heats up to immense temperatures due to its high electrical resistance and therefore produces light. Click here to read more about Tungsten Filament In Light Bulbs.
As for electronic light bulbs, we are referring to bulbs that don’t follow the characteristics of resistive loads with the use of electronic components. This refers to bulbs such as LEDs and CFL bulbs.
Resistive Bulbs (Incandescent & Halogen)
When it comes to resistive bulbs the brightness of the bulb is directly proportional to the energy it consumes. This is because resistive loads have a natural relationship between the volts and current that goes through it, meaning that the resulting light produced ends up being proportionate.
This is also likely the origin of why people commonly refer to light as a unit of power (W) instead of Lumens (lm), which is a more accurate way of describing a quantified amount of light. Because when the relationship between light and power is linear it doesn’t make a difference which unit you use, so the unit which is actually used in calculations became the more popular choice.
Electronic Bulbs (LEDs)
As for electronic bulbs, the brightness of the bulb is not proportionate to the light it produces. CFL and other fluorescent lighting are generally not meant to be dimmed, so we can exclude them when referring to their dimming characteristics, leaving us with LEDs to discuss.
The perceived brightness of an LED relative to the power we supply it with actually works out to be somewhat logarithmic in nature.
Our eyes perceive an LED which is powered at 25% of its max power to be close to its maximum light output. This means that there is a large discrepancy between how much the LED is actually powered and how bright we perceive it. To read more about this phenomenon and the nature of this characteristic I’d recommend you have a look at the article linked here.
In order to counteract this effect most LED drivers supply the LED with power with the opposite “polarity” to how our eyes work. This offsets the effect of irregular light increments, meaning that the light from an LED dimmer then becomes perceived as linear.
Dimmer Switches vs Traditional Switches
Knowing how most lights end up being linear in their light production in relation to their brightness, how does that actually affect their energy savings compared to regular light switches?
Since the light produced by a bulb is directly proportionate to the energy it uses, it means you save as much energy as the light is dimmed. If you dim the bulb to 50% of its maximum brightness it will also save 50% of the energy it would normally use at maximum light.
Knowing this, the amount of energy you save when using a dimmer switch will also depend on how often the lights are being used.
For example, it is common for offices to have an active time of 2500 hours per year. If the lighting for an office that follows this is dimmed to 80% of its max capacity we end up only using energy which would normally only get us 2000 hours of illumination.
That said, when doing an analysis of energy consumption for buildings it’s common to use a multiplier of 0.86, which implies savings of 14%.
Benefits Of Using Dimmer Switches
Other than saving energy there are also plenty of other benefits to using dimmer switches. One is that you are able to regulate the lighting to the level you desire, instead of constantly having the full power of the bulb shine like it would using a toggle switch.
Another benefit is that dimmer switches are actually likely to make your lighting last longer.
The reason why dimmers make light bulbs last longer is because of the heat buildup. Every light bulb produces some level of heat, all of which affects the bulb negatively as excess heat causes the bulbs to deteriorate and be damaged quicker than if they were cool.
Because of this, dimmer switches help these bulbs last longer. When the power of a bulb is lower than its maximum capacity it will generate less heat, and therefore cause it to last longer. This is similar to being able to do a short but fast sprint compared to a long endurance run.
How Dimmer Switches Work
To fully understand how dimmer switches have the capability to save energy we should first look into how they work in the first place.
There are multiple different ways a dimmer switch may work since there are multiple different types of light bulbs which all function best with different forms of dimming. That said, there are a few methods which are fairly common. The absolute most common way dimmers work is through a process called PWM.
PWM stands for Pulse Width Modulation and it refers to the way the dimmer modulates the width of the sine wave pulse that the electrical current has. If you decrease the wave it will subsequently decrease the brightness of the light due to some of its power per second being cut off.
There are two ways PWM dimming is done, which are leading edge and trailing edge dimming. This simply refers to if we are modulating the leading edge or the trailing edge of the sine wave.
While this is the absolutely most common way dimmers tend to work there is also AWM dimming, which means Amplitude Width Modulation. This refers to the dimmer modulating the amplitude of the wave, meaning it flattens it out to a desired level in order to decrease the brightness.
Click here for my article How Are LED Bulbs Dimmed where I explain PWM and AWM dimming in more detail.
Factors That Determine The Effectiveness Of Dimmer Switches
Now that we’ve established the function of dimmers we can begin to look at some factors that determine how effective they end up being at saving energy.
The Type Of Light Bulb
The first thing to consider is the type of light bulb you are dealing with. The reason this is important is that all light bulbs aren’t dimmable.
For example, fluorescent bulbs aren’t meant to be dimmed and LEDs are often non-dimmable too. Click here to read my article Which Light Bulbs Are Dimmable And Which Ones Aren’t? to get a better understanding of which bulbs tolerate dimming.
Another factor to consider is the efficiency of the bulb itself. For example, you can have a 7W LED bulb and a 60W incandescent bulb which both produce the same amount of light.
If you theoretically dim both of these bulbs by 50% you would save roughly 30W on the incandescent bulb and 3.5W on the LED one. Because of this, dimmers become increasingly more effective the less energy efficient the bulb itself is since 30W is far more energy saved than 3.5W.
Another factor which can determine how effective a dimmer switch will be is the ability to make use of natural daylight.
In light design and energy consumption calculations, there is the term “daylight compensation”, which describes the ability of a building to utilize the natural incoming sunlight in conjunction with the installed lighting.
The way this works in practicality is that you dim the lights when there is sufficient incoming sunlight, meaning that you use the sunlight to “compensate” for some of the lightings you would otherwise supply with the installed lights.
This helps save energy since you aren’t using electrical energy to produce light and instead make use of sunlight. The amount this saves depends on factors such as how many windows are in the room and its geographical relation to the sun, but this method can also save another 10% of the energy used.
The last factor to consider is absence detection. While most dimmers don’t normally have a function for this, there are dimmers on the market which are either programmable to turn off after a certain amount of time or that have a built-in absence detection system.
Detecting the absence of people in a space is extremely useful for saving energy since the most wasteful light is active light in areas where there are no people.
Therefore, using absence detection in conjunction with dimmers can also save a lot of energy. When this principle is used to its maximum potential we can expect energy usage to drop by around 18% (0,82 multiple), which is a number stated in the European Standard EN 15193-1.
Yes, dimmer switches can save energy when used optimally. The expected energy savings from using a dimmer switch are normally anywhere between 5-20%, with 14% being a standard number used to calculate energy savings for commercial buildings.
However, the actual amount of energy saved depends on a variety of factors, such as the type of light bulb being dimmed and sunlight compensation.
Additionally, using a dimmer switch allows you to regulate the lighting to the desired level and can have other benefits beyond just energy savings.