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In the world of LED lighting, dimming is an important consideration. We take a simplified look at what is dimming, the different methods to dim LED lights, how they work, as well as the various types of LED dimmers that need to be compatible for a successful outcome.
Our comprehensive, yet quick and easy guide to dimming basics.
Table of Contents
Dimming is the method of reducing the output of light from an artificial lighting source. When a lighting fixture or bulb is dimmed, the lumen output of the light source is decreased, lowering the lighting levels in a room.
Dimming can be used for a variety of purposes, such as reducing energy consumption, creating different lighting effects, or extending the life of light bulbs. In lighting design, there are two main types of dimmed lighting: active dimming and passive dimming.
Active is where the power to the light source is actively reduced and there are many ways of doing this, while passive relies on a material that absorbs light to reduce the output.
Dimming works by reducing the amount of power that is supplied to the light source controlled in a number of ways, commonly using a wall mounted dimmer switch. These days smart phone or tablet apps are popular whilst sophisticated systems integrate wider building control through wall mounted touch screens.
The overall light output is reduced by reducing the voltage to the LED or by reducing the reducing the AC current.
LED is now the primary source of lighting and it can be dimmed. However, LED requires careful planning and there are a variety of types to be aware of.
Most LEDs in use today are constant current or constant voltage and require a power supply called a ‘driver‘ to convert the AC current from a lighting circuit into a low voltage DC current that is suitable for the type of LED chips being used in the fixture.
When dimming lighting, the driver has to be compatible with the control method being used in the room or building.
The driver is either incorporated internally in the product or you have to pair a suitable external driver with the LED fixture or series of fixtures being installed.
Many LEDs come with built-in drivers that allow them to be dimmed using one of the many methods available.
To dim an LED with an internal driver, you will need a compatible dimmer switch, and be sure to check that it is indeed dimmable. Internal drivers cannot be accessed or replaced without potentially nullifying the warranty.
The reason internal dimmable LED drivers are used is to provide a space-saving and often more aesthetically pleasing solution, as well as reducing installation costs.
Lighting fixtures with internal dimmable drivers include:
If your LED does not have a built-in driver, you will need to use an external driver with a compatible dimmer switch.
External dimmable drivers are used when an internal driver is not suitable or practical. They are also useful when upgrading older lighting to LED, or when installing new lighting in a large area where multiple fixtures will be used.
The reason external dimmable LED drivers are used is that they can be located away from the light source, often in a more convenient location. They are also easier to replace if they fail.
Lighting fixtures with external dimmable drivers include:
There are various ways to reduce power from reaching a light source and each of these methods have been adopted within interior and exterior lighting schemes.
Phase control is the most common type of dimming used with LEDs. It works by reducing the amount of time that the power is supplied to the light source. The duration of the power cycle is shortened, which reduces the overall light output.
There are two types of phase control: leading edge and trailing edge.
Leading-edge phase control reduces the power at the beginning of the cycle instead of the end. This can result in a smoother effect and is often used with low-voltage LEDs.
Leading-edge dimmers have traditionally been more popular than trailing-edge ones. They have been around for a long time and are usually used to dim traditional incandescent and mains halogen light bulbs. This makes them better for higher wattage bulbs with capacities up to 1000W, but they can also work with LED light fixtures but rarely acceptably across the whole of the dimming curve.
Trailing edge phase control dimmers are the opposite of leading-edge phase control dim. The power is reduced at the end of the cycle, which can result in a more abrupt effect.
Trailing edge dimmers existed before LEDs were a useful light source but particularly became popular in the age of LED as it’s a method of shortening the alternating current to the light source was proven to be more tolerant to the lighter loadings of LED.
0 to 10 volt dimming is a control method used mostly in architectural and commercial lighting. It sends a unipolar signal (two wires) from the controller to the driver, which then sets the power output to the light from 0 to 100%.
0-10V Dimming works by passing low voltage power through a resistor to create a voltage drop and dim the light.
0-10Vdc was a standard control signal in the lighting industry and it is still used with DALI lighting systems.
The 1-10 volt control system is commonly used in commercial lighting applications. It is the same method as 0-10V, using a pair of wires to send a signal from the controller to the driver that is separate lighting power wires, which then sets the power output to the light with a brightness from 10-100%.
PWM Dimming is Pulse Width Modulation and a type of DC dimming.
PWM is a type of digital dim that works by rapidly turning the light on and off. The speed at which the light is turned on and off determines how bright it appears to be.
PWM creates the illusion that the light is reducing when it’s actually just being turned off and on really quickly.
DALI is a digital protocol that is used to control lighting. It allows for the dimming of LEDs and other light sources using a variety of methods, such as 0-10V, trailing edge and leading-edge.
Digital Addressable Lighting Interface (DALI) is a two-way digital communication protocol that allows lighting fixtures to be controlled and monitored individually or in groups.
DALI is often used in commercial lighting applications, but it is also becoming more common in residential applications.
Some LED fixtures come with built-in dimmers. These are often 0-100% dimmers that can be used to dim the light output of the fixture. However, not all fixtures with built-in dimmers are compatible with all types of LEDs.
Built-in dimming is a feature that some LED light fixtures have where the dimmable function is built into the fixture. This means that there is no need for an external dimmer or controller. Eg, with a touch dim table light.
A leading edge phase control dimmer is a type of 0-100% dimmer that reduces the power at the beginning of the cycle. Leading edge phase control dimmers are often used with low-voltage LEDs and can result in a more gradual dimming effect.
A trailing edge phase control dimmer is a type of 100-0% dimmer that reduces the power at the end of the cycle. Trailing edge phase control dimmers are often used with high-voltage LEDs and can result in a more abrupt dimming effect.
Retractive switch is a type of dimmer that uses a physical switch to control the light output. Retractive switch dimmers are often used in residential applications and can be used with a variety of different light sources, including LEDs, incandescent, and halogen bulbs.
Push to dim is a type of dimmer that uses a physical button to control the light output. A depress of the button cycles through the levels of light output, while a hold of the button turns the light off.
A rotary dimmer is a style of dimmer that uses a physical knob to control the light output. Rotary dimmers will utilise 1-10V, trailing-edge or leading-edge protocols.
A slide dimmer is a type of dimmer that uses a physical slider to control the light output and use a variety of protocols.
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