Michael Lane LC

archived articles

Common Areas
February 1997

With the lighting operating 24 hours per day in the common areas of apartments, condominiums, and hotels, can energy efficiency be balanced against cost, quality and style?

One-hundred watt A-lamps dot the center of the corridor, 10 feet apart, as you walk down the hall. A utility auditors dream right? From an energy standpoint yes, all we have to do is retrofit the luminaires with twin 13 watt CFLs and the energy bill will drop by two-thirds. The utility is happy, because they reduced the owner's utility bill and can now sell the power to another client. The client is happy, because the power bill went down, the luminaires don't need to be relamped nearly as often, and maybe the utility helped pay for the installation. The contractor is happy, because they completed another job and got paid. But what about the occupants of the space, are they happy? If the occupants are not happy, how long will the owner be happy?

First, I think that retrofitting the incandescent luminaires to compact fluorescent is a great idea. The color of the CFL is more than acceptable for most installations. The maintenance reduction is fantastic--750 - 1000 hours for standard incandescent, versus 10,000 hours for the CFL. Even at 1000 hours, the incandescent will last only 42 days on average. The CFL on the other hand will last 417 days on average. As a personal note, I installed a screw-in CFL that lasted over 2 years on continuous burn. Yes there are long life incandescent lamps that can last 12,000 hours, but what about light output?

Which leads to a important consideration, lumen output. All too often in the zeal to save energy light output is not considered. According to table 1, the correct CFL replacement for a 100 watt incandescent is 26 watts. Also notice that the long life incandescent lamp has a lumen output comparable to slightly less than a 75 watt incandescent. In that case the 105 watt long life incandescent could be replaced with a 18 watt CFL resulting in a 82% energy savings.

So now that the correct wattage replacement has been chosen, will it fit into the luminaire? Over the past few years CFL's have gotten smaller and smaller. Still, many downlights, ceiling-mounted luminaires and wall sconces defy retrofit. Even if the CFL fits, how does the luminaire efficiency change? That is a tough question to answer, the luminaire was not designed around the CFL so it probably will not produce the same light output. Even if the luminaire efficiency is the same, what about the lighting distribution? I'm sure you all have seen the downlight or wall sconce with the CFL sticking out of the luminaire. Very efficient!

Speaking of lighting distribution, where is the best place for the light in a corridor situation? My vote would be on the walls or the ceiling. Downlights that just light the floor can be very dramatic, but what about safety, and the sense of security? Light on the walls and the ceiling will go much farther in producing a secure feeling space than light just on the floor. Light on the walls and ceiling will also reduce the contrast between the luminaire and its surroundings, reducing disability glare.

Often the best choice is not to retrofit, but to replace to a new luminaire. Manufacturers today are producing a significantly greater variety of downlights, ceiling luminaires and wall sconces that use the CFL than ever before. Yes, new luminaires cost more than retrofitting the existing, but what is the real cost? New luminaires are designed around the CFL shielding the lamp from view, most of the time, and producing proper lighting distribution and luminaire efficiency. Should you really retrofit that 20 year old luminaire? Hasn't it already had a useful life?

Remember our first example, the 100 watt incandescent to 26 watts of CFL. Even though we provided the same initial lumens in the retrofit, because the luminaire was not designed around the CFL we may not get the same lumens out of the luminaire. We need to do the retrofit, due to energy concerns, but weight all of the issues and talk seriously with the client about new products. You may still decide to retrofit, and that's okay. Because either way we get the energy savings, and that's the most important issue, isn't it?