Dimming Ballasts

Dimming fluorescent lighting instead of repeated switching helps to maintain lamp life. Dimming also saves electricity and reduces the demand on HVAC systems. Lighting output is adjusted to predetermined levels set during the commissioning process. A dimming unit smoothly varies the light output of electric lights by altering the amount of power flowing to the lamps. If daylight is less than the target illuminance, the control increases the lighting to provide the right amount on the work plane. Dimming controls in some situations save more energy than switching if they are linked to daylight and if lamps are dimmed at the start of their lifetimes to compensate for their increased output. Dimming controls are less obtrusive to occupants than switching, but a manual override is recommended in areas where occupants expect to have control. Switches can also used instead of dimmers, but this is not recommended except for limited applications because they are more obtrusive and may use more energy than dimming switches. High frequency dimming produces the greatest savings in all but the most well daylit rooms. A problem with photoelectric switches is rapid switching on and off when daylight fluctuates around the switching illuminance. This can annoy occupants and reduce life. Various techniques have been developed to reduce the amount of switching. Multi-level switching control uses two switching illuminances, one at which the lights are switched off and another, lower illuminance level at which the lights are switched on. Photoelectric switching with a time delay can also introduce a delay in the switching process.

Dimming ballasts replace non-dim ballasts in fluorescent fixtures, improving the energy performance and flexibility of any space.

Dimming is important because the human eye responds to low light levels by enlarging the pupil, allowing more light to enter the eye. This response results in a difference between measured and perceived light levels. A lamp that is dimmed to ten percent of its maximum measured light output is perceived as being dimmed to only 32 percent. Likewise, a lamp dimmed to one percent is perceived to be at ten percent. Descriptions of different levels of dimming follow:

• One percent architectural dimming provides very fine light level control to users for aesthetic effect or for very stringent lighting or audiovisual design criteria. Architectural spaces often have a strong focus on aesthetics and comfort, creating an environment that portrays class and distinction. Architects and designers create these spaces for maximum versatility and require subtle control of the lighting. Room types: theater, auditorium, lobby
• Five percent high performance dimming offers energy savings, aesthetic appeal, and space flexibility, allowing users to operate their lights at 100%, 5%, and anywhere in-between. Room types: meeting rooms, classrooms.
• Ten percent lighting management dimming works well for a classroom, cafeteria, or office lighting application. To maximize the benefits of a lighting management system, use dimming ballasts. Ten percent dimming is ideal for use in any space where saving energy is a primary goal. Room types: most spaces including classroom, library, cafeteria, meeting room, graphic art workstation, office, corridor/stairwell, utility room, restroom

Manual dimmers are available for incandescent, fluorescent, and certain high-intensity discharge (HID) sources. Both step and continuous dimming are available for incandescent fixtures. Multiple dimming methods are available for both fluorescents and HIDs, though HID dimming is limited by color rendition and flicker problems. Experience has shown that manual controls are not used effectively. Many occupants leave electric lighting on once it is switched on even if the illumination from daylight is at a level that would be considered adequate if the occupant were entering the space. Today, there are a number of light control systems that can cap the maximum light level provided by a manual dimmer, reducing the electricity used when lights are left on. Energy savings cannot be realized in daylit buildings unless the electric lights are dimmed or switched in response to the amount of available daylight. The energy savings achieved with daylight-responsive lighting controls will depend on the daylight climate, the sophistication of the controls, and the size of the control zones. An evaluation of currently available responsive control systems is presented in the International Energy Agency Solar Heating and Cooling (IEA SHC) Application Guide. This evaluation has shown that daylight-responsive systems used up to 40 percent less than non-controlled systems. Cooling load reductions have also been noted, which can save an additional two to three percent of electrical energy consumption. Savings can be larger than 40 percent especially in toplit spaces. In hot climates, the cooling savings can also be larger.