The importance of dimming
Dimming can be used to enhance the ambiance of a space, increase visual acuity, and customize lighting based on the task. A single fixture can be dimmed to many levels, allowing one fixture to be used for multiple applications while minimizing the number of products to specify for a location.
Dimming can be used along with occupancy sensors and daylight harvesting to save energy while still meeting the lighting needs of a space.
In addition, LED is the only lighting technology that gets more efficient as it is dimmed. Dimming even increases the lifespan of LED products.
Types of driver controls
There are different kinds of dimming controls. One way-controls (phase dimming, PWM, 0-10V) are simpler, but two-way controls (DMX and DALI) allow for greater functionality.
The majority of installed dimmers are phase dimmers. Phase dimming involves clipping part of the sine wave to deliver less power to the light source, resulting in a dimmed light. There are two types phase dimming.
Forward phase (leading edge) dimming was commonly used for incandescent and halogen lighting. The front of the wave is clipped. This type of dimming is suitable for inductive and restive loads such as incandescent bulbs and magnetic ballasts.
Reverse phase (trailing edge) dimming clips the back of the sine wave. This is suitable for capacitive loads such as LEDs. Forward phase is not suitable for these loads since the capacitors do not have time to charge, resulting in flickering light.
Pulse Width Modulation (PWM) is a method of dimming that turns the light source on and off, faster than the human eye can see. When the light is on longer than it is off, it appears brighter. When it is off longer than it is on, it appears dimmer.
This method requires separate AC power and control signal. LEDs themselves dim using PWM, but the fixture doesn't necessarily support the varying input. Often, the fixture receives an input in the form of a voltage which tells the control circuitry how much to modulate the LED.
0-10V dimming has a pair of wires with a differential of zero to ten volts. When this value is 10V, the light runs at maximum brightness. 5V results in 50% brightness.
There are two different standards which function the same, except the minimum value is either 0V or 1V. In fixtures where the minimum is 1V, the light will be at 10% without actually shutting off. In fixtures where the minimum is 0V, the fixture will turn off if dimmed all the way.
DMX & DALI
DMX and DALI (Digitally Addressable Lighting Interface) are two-way communications that differ in their topology. They both allow for control of a large number of individually-addressable fixtures. Neither of these protocols are proprietary, allowing them to be used on fixtures from virtually any manufacturer.
The ease of programming DMX512 makes it widely used in theatrical and architectural lighting, such as schools, gymnasiums, auditorium, and churches. There is a master controller and each device needs a decoder to translates to the correct "language" for the device.
Luminaires can controlled as an individual fixture or as a group. These communication protocols allow for RGB control and movement of fixtures where applicable.