It’s well documented that lighting electric loads can represent 20% to 25% of the total electricity used in industry, and that energy-efficient equipment can have a positive effect on any facility’s operations. Improvements in fluorescent technology (lamps, ballasts and luminaires) have led to opportunities for facility managers to leverage lighting as an energy-management tool. And that tool addresses operational and cost issues, as well as improvement in productivity, comfort and image.
The lighting industry continues to introduce products and technologies focusing on efficiency improvements from both a quantitative and qualitative standpoint. These innovations include advances in the fluorescent lamp/ballast technology, new generations of T-8 and T-5 lamps, and properly matched electronic ballasting. These enhancements are greatly influenced by the lamp/ballast combinations and their performance in a specific luminaire.
Energy-saving T8 lamps
The introduction of T8 technology in the early 1990s led to practical replacement of the less efficient T12 lamp system. Now energy-saving 25 W to 30 W lamps can replace standard T8 lamps and provide energy savings from 5% to 20% without a T8 ballast change. This provides an inexpensive retrofit alternative while keeping the good color rendition, high efficacy and long life advantages of T8 lighting.
Facility managers and end users need to understand the post-changeover performance in terms of light output and energy consumption. These new lamp technologies have varied light output ratings. From an application standpoint, a changeover should take into consideration the current quantity (light levels, uniformity) and quality (color, glare) requirements.
These lamps have similar efficacy performance levels, and thus the lumen percentage values represent the energy savings. The values should be used as representative figures because each manufacturer publishes different values and the actual energy consumption can vary depending on the lamp/ballast combination performance. Additional energy savings – as much as 35% – are possible by matching a specific ballast to the new T8 lamp versions where a ballast with a ballast factor (BF) of 0.77 operating three 25 W lamps delivers the lowest power consumption.
The “super” T8s feature improved components and manufacturing techniques that allow manufacturers to increase lamp lifetimes to more than 24,000 hours to 36,000 hours and raise light output levels by 10%. Note that fluorescent lamps have been rated at an average life (50% survival rate) of 20,000 hours under a duty cycle of three hours on and 20 minutes off.
Manufacturers have started publishing longer lifetimes when operating these lamps on duty cycles that are more representative of their actual operation (10 hours to 12 hours per day). Another way to improve lamp lifetime is to control the electrode sputtering during each start cycle. Program-start ballasts are thus preferred because they provide a much “softer” lamp ignition. Instant-start ballasts, on the other hand, reduce lamp lifetime by 15% to 25% if the lamp isn’t designed for that type of start.
The new T5 lamps have a 40% smaller diameter than a standard T8. This difference permits the use of more compact housings with optimized optical designs. Furthermore, T5 systems provide optimum light output at 35°C ambient temperature, which is 10°C greater than the peak light output performance of T12/T8 lamps. This behavior allows T5 systems to operate closer to their optimum light levels when enclosed in a fixture, resulting in more delivered light.
T5 systems are offered in high-output (HO) versions, which require fewer components to achieve the required light levels on the work-plane. Manufacturers and research organizations publish data comparing light output and wattage consumption of various two-lamp T8, T5 and T5HO systems. The advantage of fewer luminaires is possible only if the luminaires are able to control glare.
Selecting the appropriate lamp/ballast combination has become more complex because of the multitude of offerings. This is an advantage for the end user and specifier. Electronic ballasts perform better than magnetic units. The reason is reduced ballast losses and high-frequency operation. Coupled with controllability and dimming management, electronic ballasts help drive the industry to a 100% electronic market, as mandated by government regulations. In fact, the market has embraced electronic ballasts as the preferred choice for additional reasons such as reduced noise levels, flicker-free operation, controllability of harmonic distortions and power factors, to name a few.
Using the table data for a typical 10 ft. by 12 ft. luminaire spacing, it’s possible to achieve 0.6 W/sq. ft. energy loads with a three-lamp T8 system using the low ballast factor version. Moreover, using an energy-saving F25T8 lamp would produce 0.5 W/sq. ft. energy loads. Another design option would be to consider selecting a high-light output system (ballast factor of 1.2) and luminaire spacing of 14 ft by 16 ft. With adjusted spacing, these systems can yield 0.5 W/sq. ft. energy loads, but with fewer luminaires and reduced investment.
Recessed luminaire optics
The two types of luminaire optical designs for interior spaces are directional and diffuse. Directional lighting uses the optics from the reflector housing, coupled with the optics from the louvers (aluminum baffles), which are parabolic in shape and act as a glare shield.
Diffuse lighting systems usually have higher efficiency ratings (>85%), but will “throw” light everywhere with less control of the distribution. The occupants of the space might be subjected to glare.
Indirect lighting, a type of diffuse lighting design, is reported to be easier on the eyes and a preferred lighting system. The efficiency ratings are low (<50%) because the luminaires reflect off the ceilings. They should be evenly distributed to avoid excessive luminance. Like an overcast day, indirect lighting can provide a calm, diffuse light without highlights or shadows.