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archived articles Retro-fit Reflectors How may times have you heard, "We can take two of the four lamps out of the fixture, add a specular reflector and you'll get the same light level?" I've lost count. This is simply not true. But with the rush to save energy across the country, many facilities and business owners have believed in miracles and bought these systems. You can't halve the number of lamps and achieve the same average maintained footcandles. The numbers just don't add up. The existing system the Luminaires may be 15 years or 20 years old, or even older, and the many light loss factors have reduced the manufacturer's initial rated lumens. The lamps have depreciated, some may even be burned out, the lens has yellowed, and dirt has accumulated on the lens, lamps and reflector. A good lighting designer always considers maintained light levels, not initial light levels. Rarely are maintained lumens calculated when a retrofit reflector is added the luminare, so the comparison of these two systems is not apples-to-apples. So let's compare two systems to determine the gain from this retrofit: the 4-lamp lensed fluorescent versus the 2-lamp lensed fluorescent with specular reflector. The total luminaire efficiency of a new 4-lamp luminaire can range from 65 to 70%. Take the four lamps times 3050 lumens/lamp times 65% luminaire efficiency (I'll be conservative) and the result is 7930 lumens delivered. Let's stop right here and examine total luminaire efficiency. If the above theory holds true, a 2-lamp retrofitted luminaire must have a total luminaire efficiency of 130 to 140% to deliver the lumen output of a 4-lamp luminaire. That's one impressive reflector system! Most retrofit systems have a total luminaire efficiency, not reflector efficiency, of around 80-85%. Two lamps times 3050 lumens/lamp times 85% luminaire efficiency (I'll be optimistic) and the result is 5185 lumens delivered. This is only a 15-20% increase in luminaire efficiency, and will produce 35% lower average maintained footcandles! The only consolation that most business owners have is their existing lighting system may be providing twice the IESNA recommended light levels, so a 35% reduction will still provide adequate light levels. To boost lighting back up to its original level, many retrofits will involve additional component changes. Often the lens is replaced to improve transmissivity and, if the lens has yellowed, color. But this change can be done without adding the retrofit reflector. Similary, other retrofits include a new 2-lamp T8 electronic ballast, which reduces the energy consumption even farther and is a good thing to do, but this also can be done without adding a retrofit reflector. So, should you consider the additional cost of a retrofit reflector system, or are there other, less expensive, ways to achieve a 20% efficiency gain from a lensed 2-by-4 fluorescent luminaire? One option is to use a high-ballast factor T-8 electronic ballast. Ballast factor is the ratio of actual lumen output of the lamp on a particular ballast to the rated lumen output on a reference ballast. Your present system of a magnetic ballast with F40 T12s has a ballast factor of 94%; using 34 watt energy-saving lamps brings the ballast factor down to 87%. All of the following ballasts are designed to run two T-8 fluorescent lamps and have high ballast factors. The only drawback to this reballasting strategy is that as the ballast factor goes up, so does the wattage, reducing energy savings. So what is the best choice? Well, all of hte above should be considered, but:
But remember it's your choice and your money, make an informed decision. |
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