Dimming is the process of controlling the amount of electrical power supplied to a light source. The four most popular methods for dimming LED lights are described below and cover 0-10Volt dimming, PWM(Pulse Width Modulation) dimming, Forward-Phase dimming(sometimes referred to a “Triac” or Incandescent Dimming) and Reverse-Phase dimming(sometimes referred to as an ELV or Electronic Low Voltage Dimming).
This method can use a number of devices to control the dimming. This requires additional low voltage wiring, but is more accurate than AC phase dimming.
0-10V dimming applies a direct current voltage (DC) between 0 and 10 Volts to produce light at varying intensity levels. At 10V, the lights controlled by the dimmer are at 100% brightness. At 1V, the lights are at 10% measured brightness, which may actually be perceived as 32% brightness. Read this blog post to find out why. At 0 Volts, it either turns the lights off or has the lights dimmed to the lowest possible level and a switch is required to turn the lights completely off.
0-10V dimming started as a method for dimming fluorescents but is also used on LED lighting today. It’s typically used in offices, retail spaces, and homes with fixtures that have an LED driver designed for 0-10VDC dimming input. While it can be used for RGB or RGBW color-changing lights, there are some limitations. Each of the three or four colors needs to be assigned a zone so that the controller can adjust the intensity of each color separately to produce a range of color possibilities. If the color changing lights require additional inputs beyond intensity, a different dimming method should be used. For applications like entertainment spaces and those epic Christmas light displays that inspire “Ditto” lights from the neighbors, it’s common for people to use DMX512 protocol products instead, allowing them to connect the lights to a computer.
Pulse Width Modulation (PWM Dimming)
PWM is a dimming method that is prevalent in LEDs that use constant-current drivers. This technique works by adjusting the duty cycle of the current, resulting in changes to the average current in the string. PWM is effective for accurate light dimming requirements, as it can handle high dimming ratios at 100 Hz (high frequency, so that the human eye cannot detect the flickering effect), with minimal effects to the LED color/color temperature. To achieve dimming, the LED is toggled at a very rapid rate. For instance, at the highest setting (full output), the LED stays “on” and is never toggled. At 75 percent dimming, the lights are only “on” 25 percent of the time. When plotted on a graph, shifts in current appear to be staggered, like a set of evenly spaced blocks or stairs without a long-term ascending or descending pattern (rates/values of dips/increases are constant).
This type of dimming is ideal for lighting systems that need to be dimmed below 40 percent in a very consistent manner. PWM is suitable for color-mixing requirements, due to its precise dimming properties. Lastly, it can be incorporated in electronic systems via direct digital control.
Also commonly knowns as “Triac Dimming”,”SCR Dimming”,and Forward Phase control dimming, Forward Phase dimming control is the most common form of phase dimming. It uses a silicon device, usually an SCR or a Triac, to turn the mains waveform on part way through its cycle. By varying the point at which the waveform turns on, we can alter the amount of power delivered to the load.
It is a the cheapest, relatively simple and widely available technology but a drawback is that it often causes buzzing.
The switching from zero to peak of the wave is enough to cause vibrations in the electronic components as a surge of electrons move each time. If the vibration is strong enough, the dimmer, and sometimes the lamp, will buzz.
Trailing Edge (ELV) is a more advanced technology designed to combat buzzing. It works in the same way as leading edge, by switching off the signal twice every wave, but it switches off the end of each cycle.
Trailing-edge dimming causes less buzzing because each time the wave is switched on, the wave is at the lowest strength of the cycle and gradually grows bigger.
As there is no sharp difference between off and the state when first switched on, and the current gradually increases there is less chance of a vibration being caused. Without vibration, there will be no buzzing.
The technology is widely available but the more complex electronics means that it is more expensive to manufacture.