Dimmers

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Introduction

Dimming of lighting equipment requires specialized control hardware that is based on the source type to be dimmed. Standard incandescent systems require very simple voltage control, while fluorescent lamps require special dimming ballasts. Different source and ballast types determine the type of control hardware required. For ballasts, this is dictated by the source type and/or the control protocol being used to communicate between the lighting control equipment (wall box controls, scene controllers and other devices) and the dimming ballasts. The different source type and control options that may affect the dimming hardware required include at least the following:

  • Line voltage incandescent and halogen
  • Low-voltage halogen with magnetic transformers
  • Low-voltage halogen with electronic transformers
  • Fluorescent (0-10V dimming ballasts)
  • Fluorescent (two-wire dimming ballasts)
  • Fluorescent (three-wire dimming ballasts)
  • Fluorescent (digital dimming ballasts)
  • Dimmable CFLs
  • Dimmable LEDs

A wide variety of wallbox dimmers are available with internal hardware to dim individual loads up to the rated wattage of the control device. At higher wattages, or when multiple circuits must be dimmed, dimming racks or panels are typically employed. In these situations, the wallbox device simply signals the dimming modules in these panels to modify the voltage or power delivered to the lamps. For retrofit screw-base compact fluorescent lamps (CFL’s) and Solid State Lighting (LED) sources, the sources must be rated as a dimmable source and the dimmer must be compatible with dimmable CFL and LED sources. Older and standard incandescent-rated dimmers may not be compatible with these retrofit lamps. Many current dimmers state they are compatible with these new dimmable energy saving sources.

As electric light sources are dimmed, lighting energy is reduced. With filament lamps (incandescent and halogen), light output drops faster than input watts to the lamp, causing the source operate at a much lower efficacy. With fluorescent sources, the lumen output to power curve is very linear, running from maximum output and power to a minimum light output of approximately 1 to 5% for modern dimming ballasts, which requires approximately 20% of full input power. Check manufacturer’s data for actual values.

Section Key Resources

Lead Author(s): Rick Mistrick

HID

The dimming of HID lamps has received significant attention recently due to requirements in many energy codes for multi-level zone control. Both 0-10V and stepped ballasts are now available for metal halide and HPS lamps to accommodate these codes. Stepped HID dimming often provides dimming to 50 percent power, which corresponds to approximately 30% of full light output. Step-dimming ballasts operate by switching the capacitors that are applied to the lamp circuit using internal relays. For continuous dimming, dimming below 50% power can result in reduced lamp life and is not recommended.

Not all HID lamps are dimmable. Certain types of HID lamps can only be dimmed in a base up burning position (or within 15 degrees of this position), while others can be dimmed in any burning position. Consult manufacturer’s data if stepped or continuous dimming of HID lamps is being considered.

Another requirement when dimming HID lamps is that HID lamps must be started at full light output and operate at full output for 15 minutes prior to being dimmed.

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Lead Author(s): Rick Mistrick

Solid State (LED)

LED sources are powered by a driver, which provides direct current (DC power) to the individual LED chips. When applied on a standard incandescent dimmer, the power delivered to the driver is altered, typically by cutting out a portion of the sine wave. To work properly, the LED driver must be designed to operate under these conditions. Some LEDs that are capable of operating on incandescent dimmers can be dimmed down to approximately 15-30% of full light output. Below this point, the LED driver does not receive enough power to operate properly. To achieve lower levels of light output, LED drivers can be designed to modify the power delivered to the LED chip. These typically receive unaltered power from the electrical system along with a signal, such as a 0-10V signal or some other control protocol signal, and then provide the appropriate pulse width modified power to the LED to dim the source.

Section Key Resources
  • No publications specific to this section have been listed.

Links

Lead Author(s): Rick Mistrick

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