Michael Lane LC

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Energy Codes
November 1995

Do you live in a state that has energy codes? California, Massachusetts, New York, Oregon, Washington, and other states have existing energy codes that restrict the total amount of energy that can be used in a lighting system. For years designers in these states have had to design lighting systems that meet these maximum lighting power density requirements (measured in watts per square foot) while meeting IESNA recommendations for illuminance levels, and providing a quality lighting environment.

However, if you live in or work in a states that does not have an energy code, are you free to design the lighting system however you wish, without regards to energy efficiency? Not any more. The Energy Policy Act of 1992 requires all states to demonstrate that the energy-efficiency requirements of their commercial building codes, meet or exceed the requirements of ASHRAE/IESNA Standard 90.1-1989. Standard 90.1-1989 was developed in the early 1980's, so by today's standards these requirements may not be very stringent.

Are these energy codes a bad thing? Well, some may think these codes are restrictive, because you can no longer use whichever light fixture you want, wherever you want. To others it means having to actually DESIGN the lighting; no more "cookie cutter" projects. And to others it jeopardizes the lighting quality of the space.

Energy codes mean that the new lighting technologies are finally becoming main stream. T8s are replacing T12s as building standard for new construction. I will be very happy when I no longer have to explain T8 technology to designers and end-users. Electronic ballasts are less expensive, more reliable, and provide more design options with dimming and low, normal and high ballast factor options. If designers would just use the combination of T8s with electronic ballasts instead of T12s with energy-saving magnetic ballasts, initial energy consumption would be reduced by around 28% or more. This 28% reduction may be sufficient to meet many energy code requirements. Compact fluorescent are being used in place of incandescents for general lighting in corridors and lobbies. A typical two lamp13 watt compact f luorescent (1800 initial lumens) luminaire can replace a 100 watt incandescent (1750 initial lumens) luminaire in most downlighting situation.

For example let's look at a 20,000 square feet office building with a 3-lamp (F40T12) 2-by-4 parabolic fluorescent luminaire on energy-saving magnetic ballasts spaced on 8-by-10 foot centers. This luminaire would use 1.67 watts/sq.ft., which happens to meet ASHRAE/IES Standard 90.1-1989 of 1.72 watts/sq.ft. assuming there is no task lighting. But the 1.72 watts/sq.ft. limit includes "both permanently installed lighting plus supplemental task related lighting provided by movable or plug-in luminaires". Task lighting could easily use 0.5 watts/sq.ft. (one 4-foot fluorescent luminaire per work station) which will reduce the allowed ceiling lighting to 1.22 watts/sq.ft.

Several options meet this lower power density requirement. Thirty-four watt energy saving lamps with energy-saving ballasts, would lower the energy use to 1.31 watts/sq.ft., though this may not be sufficient to meet the code requirements depending on the amount of task lighting. Additionally the light level would be reduced by around 14%. A second option would be to use electronic ballast with the 34 watt lamps . This is a poor choice, because if you are going to buy an electronic ballast, you should use the better-performing T8-electronic ballast-and-lamp combination due to its better performance characteristics. The T8 lamp with an electronic ballast uses around 1.16 watts/sq.ft. without reducing the light level.

RE80 T-8 Fluorescent Lamps

With the demise of the F40 T12 cool-white lamp, due to the 1992 Energy Policy Act, it is time for designers embrace the T8. The T8 fluorescent lamp has been available since the early eighties and is far superior to the 34 watt energy-saving lamp that many end-users want to use. But remember that the T8 lamp requires a 265ma ballast, and the T12 requires a 430ma ballast. Running a T8 on an existing T12 ballast will dramatically reduce lamp life and can increase energy use by around 24% (I tested two T8s on a T12 energy-saving magnetic ballast using 107 watts).

As a comparison, the RE70 (70 CRI triphosphor) T8 lamp produces 2570-2600 mean lumens (81.25 lumens/watt) compared to a mean of 2280-2300 lumens (67.65 lumens/watt) for the cool-white 34-watt energy saver. For even higher light levels the RE80 T8 lamp produces 2650-2850 mean lumens (89 lumens/watt).

If we look at the 20,000 sq.ft. office example from above, an assumed a CU (coefficient of utilization) of 75% and a LLF (light loss factor) of 75%, the RE80 T8 lamp would provide 60 average maintained footcandles. The same system using the RE70 T8 lamp would produce 55 average maintained footcandles, and would require about 9% more lamps, ballasts and luminaires to provide the same 60 footcandles. The 34-watt energy saving lamp system would produce only 48.5 average maintained footcandles and require 20% more lamps, ballasts and luminaires to provide the same light level as the RE80 T8 lamp. The added cost of the T8 ballast and lamps, if there is one any more, will be easily be made up in the fewer luminaires needed to light the space.