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.
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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 (Table 1). 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 (Table 2) 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 (Figure 1). 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.
Table 3 provides several choices for a three-lamp T8 system, which is the prevalent lighting specification for new construction of typical offices and commercial spaces.
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.
New luminaire optics have been developed around the reflection properties of T8/T5 lamps in recessed 2 ft by 4 ft housings. This enhancement controls the brightness into the higher viewing angles.
New designs for two-lamp units can compete with typical parabolic three-lamp units. These designs deliver optimum light distribution, appeal and better energy loads. Additionally, this controlled light output can produce excellent lighting for vertical surfaces by illuminating the upper parts of the surrounding walls to eliminate the cave effect that parabolic luminaires produce.
Technology improvements in fluorescent lighting
New generation of T8 systems:
- Energy-saving 25W to 30W F32T8 systems
- T8 improvements (such as lamp lifetimes above 24,000 hours to 36,000 hours and >10% light output)
Introduction of new T5 systems
- Leading to smaller and more compact luminaire housings
- Availability of high-output versions (fewer luminaires required in the space to deliver the same light output)
Fluorescent electronic ballasts
- Increased offerings (more options)
- Varied levels of performance in terms of light output and energy consumption (low/standard/high)
New recessed luminaire housings
- Advantages of optically enhanced lighting (less glare, better uniformity in work-plane)
- High efficacy (>90%) versus typical troffer performances at 70% to 85%.
Ballast factor (BF)
The ratio of delivered lumens from the specific lamp/ballast combination to the rated lumens of that same lamp on a laboratory-standard reference ballast. Lamp manufacturers publish the latter figure as the lamp’s rated initial lumens, whereas ballast manufacturers publish BF ratings for every specific system combination.
Average lifetime ratings
The 50% survival rate of a batch of lamps. The fluorescent lamp industry determines this lifetime rating using rapid-start circuits and a standardized testing cycle of three hours on and 20 minutes off. Manufacturers now publish different lifetime ratings that represent different burning cycles (10-hour to 12-hour “on” cycles) and different starting circuits (instant start versus rapid start).
Lamp diameters (T8 versus T5)
Fluorescent lamps are identified by a number that indicates the diameter of the lamp in eighths of an inch. For example, T8 refers to an 8/8 or 1 in. diameter lamp.
Graph 1 depicts the normalized light output performance of each lamp versus the ambient temperature against a maximum percentage of 100%. In open, parabolic and indirect/direct luminaire housings, the ambient temperature the lamps experience can be 10°C to 25°C higher than room temperature because of the lamp’s heat release inside the fixture. Typical enclosed luminaires (lensed troffers) have higher temperature gradients that reduce light output to below 70% for T8 lamps.
A recessed fixture.
Open plan office area
The following is an example of a layout using the latest developments in lamp, ballast and recessed luminaire technologies.
- Approximate room size: 9,600 sq. ft.
- 10 ft x 12 ft luminaire spacing - 80 luminaires
- 2.5 ft work-plane with 80/50/20 reflectances
- Ceiling height - 9 ft
- Lamp lumen depreciation - 0.95
- 3,100 lumens/lamp (High output T8 lamp)
Electronic ballast components
- Two-lamp energy consumption - 59W (BF=1.0)
2x4 recessed luminaire
- Luminaire dirt depreciation - 0.94
- Two-lamp F32T8 optically enhanced housing
Light technical characteristics
- Average illuminance - 41.4 foot-candles
- Uniformity (max./min. - 3.28)
- 0.5 W/sq. ft.
1. Bleeker, N., Lighting Efficiency Technology Update, adapted from 2006 GlobalCon presentation, 2006.
2. Bleeker, N., Benefits of Energy-Efficient Lighting, Energy Engineering, Volume 90, No. 6.
3. Akashi, Y., NLPIP, National Lighting Product Information Program, Lighting Research Center, Lighting Answers: T5 Systems, 2002, Vol. 6, Issue 1.
4. Bleeker, N., D. Gross, and S. Johnson, Performance Studies of Fluorescent Systems, Illuminating Engineering Society of North America Annual Conference: Technical Papers, Minneapolis, 1988.
5. Houser, K.W., Tiller, D.K., Bernecker, C.A., and Mistrick, R.G. (2002). “The subjective response to linear fluorescent direct/indirect lighting systems.” Lighting Research and Technology, 34(2).
6. Vasconez, S., Ballston Spa High School (2001), DELTA Portfolio Lighting Case Studies, Vol. 3, issue 2.
7. ANSI/IESNA RP-1-04, “American National Standard Practice for Office Lighting,” p 24.
Figures: Day-Brite Capri Omega Lighting
Nick Bleeker is director of business development at Day-Brite Lighting in Tupelo, Miss. Contact him at [email protected] and (662) 620-6702.