Plant Services - May 2008 - (Page 54) efficiency Lighting 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. Some lighting choices T8 lamp output Wattage 32 30 28 25 Lumen percent 100 95 90 80 Table 1. Light output as a function of power input for T8 lamps. Ballast performance System wattage (3 T8 lamps) Lamps 32W 30W 28W 25W BF = 0.88 83 to 88 78 73 66 BF = 0.77 72 68 63 57 T8 improvements 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 now publish longer lifetimes for operating these lamps on duty cycles more representative of their actual operation (10 hours to 12 hours per day). Another way to improve lamp lifetime is to control the electrode sputterDefinitions 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. Table 2. The ballast factor has a measurable effect on your lighting power consumption. Customized lighting F32T8 Electronic comparisons Balast factor 1.2 0.88 0.77 Three-lamp wattage 112 88 72 Relative light output (%) 136 100 88 Table 3. Output as a function of ballast factor. ing during each start cycle using program-start ballasts that 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 T5 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. Ambient temperature 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. The new T5 lamps have a 40% smaller diameter than a standard T8. This difference permits more compact housings with optimized optical designs. The T5 systems provide optimum light output at 35°C ambient, which is 10°C greater than for T12/T8 lamps (Figure 1). This allows T5 systems to operate closer to 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. Electronic ballasts Troffer A recessed fixture. Selecting the appropriate lamp/ballast combination has become more complex because of the multitude of offerings. www.PLANTSERVICES.com May 2008 54 http://www.PLANTSERVICES.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.