High-quality task lighting
High-quality task lighting
Electronic high-frequency ballasts offer several advantages over standard electromagnetic ballasts: Besides improving the efficacy of a lighting system by up to 25%, they do not produce the flicker and noise characteristic of conventional ballasts, which may make building occupants tired and give them headaches.
Possibilities for improving efficacy and reducing flicker and noise from luminaires providing task illumination at the workplace are often neglected. Some European manufacturers have recently commercialized luminaires for task lighting equipped with electronic ballasts. Here are some examples of different strategies:
The Swedish/Norwegian luminaire manufacturer Luxo/Jac. Jacobsen recently presented a luminaire with a CFL and electronic ballast and advanced reflector design. In addition, the manufacturer also has responded to some of the potential problems of electromagnetic fields (EMF) associated with fluorescent lighting systems. Here, we use the popular word "electromagnetic" for both electric and magnetic fields. Hence, the abbreviation EMF. In the case of high-frequency ballasts for fluorescent lamps, EMF includes both Band 1 (ELF-Extremely Low Frequency: 5 Hz to 2 kHz) and Band 2 (VLF-Very Low Frequency: 2 kHz to 400 kHz).
The luminaire was developed to meet the ergonomic specifications used in a NUTEK project for efficient office lighting. These requirements were developed in part to satisfy requirements regarding EMF levels set by important office equipment specifiers such as the Swedish Public Building Agency. Although there is no proof today that EMF can have adverse effects on health, some people consider themselves hypersensitive to these fields. As a precaution, many Swedish employers have decided to see what can be done to address these matters at a reasonable cost.
In the Luxo luminaire, extremely low values of EMF-far below the already low requirements-were achieved by making the following simple modifications, which all are claimed to add only marginally to the cost of the luminaire.
- The whole luminaire is grounded. This includes the reflector and all other metal parts, as well as the housing which is made of metallized plastic.
- A high-quality bi-polar switch ensures that no current remains in the luminaire after it has been switched off.
- The power-supply cable is shielded.
As for the reflector, it is specially designed to distribute the light asymmetrically from the side (maximum light levels are ~0.45 m from the light source) in order to avoid glare problems. The horizontal position of the luminaire is fixed to avoid tilting and associated reflections on computer screens as well as direct glare. The lamp comes in 18-W and 24-W versions.
Another luminaire marketed with ergonomics as the argument can be found in Germany: The light source manufacturer Osram normally does not manufacture luminaires, but at times the company releases a product to inspire luminaire manufacturers. This time, Osram's message to luminaire manufacturers is to use electronic ballasts for task lighting, an application that the luminaire industry is slow in adopting. The Osram luminaire is equipped with a 26-W CFL. In the press releases accompanying the lamp, ergonomic issues and fancy design are emphasized more than energy efficiency and environmental friendliness. And to add respectability to the argument, the picture of the lamp also depicts a medical doctor writing in her patient journals.
A third example of task lighting with electronic high-frequency ballasts comes from the Belgian luminaire manufacturer Etap. They have even named their luminaire Ergolum, to stress ergonomic improvement. This model is a pendant luminaire that integrates three separate optical components:
- indirect, ambient lighting is provided by uplights
- CFLs provide direct task lighting from two directions. The carefully designed reflectors and glare shields distribute light in a way that ensures high illumination levels and high contrast while reducing glare.
Since the luminaire is made for different room sizes, the indirect lighting section comes in two versions, one for 1x32-W long fluorescent tubes, and the other for 2x32-W tubes.
The luminaire can be outfitted with a daylight-dependent dimmer for the indirect part (that also compensates for lumen depreciation) and with occupancy sensors for the part providing direct illumination. The luminaire is also outfitted with independent switches for all three sections. This combination of control technologies and independent switching should make the lighting system more user friendly.
Nils Borg
See also:Electronic Ballasts: Relief for the Senses (IAEEL 1/96)