Compliance with energy codes has become a regular part of the design process for lighting designers in recent years. Prior to the release of the 2004 version of the ASHRAE/IES 90.1 standard for energy codes, it was easy to design lighting without worrying about bumping into code limits. This was because codes had not yet caught up with energy-efficient technologies and current design practices. The ASHRAE 2004 standard was significantly more stringent in its limits on the total amount of connected lighting load allowed. It is still possible to produce quality lighting design under these limits, but much of the headroom went away. Frankly, you can’t be sloppy anymore, and this is a good thing. So, less energy use, more code compliance work for lighting designers – happy ending, right? Well, maybe.
Let’s look at the structure of U.S. energy codes as they apply to lighting. They aren’t really energy codes, they are more like power codes. The main way that U.S. energy codes regulate lighting is by limiting the amount of power (watts) that your lighting system can use. This is done by giving you allowances for maximum lighting power density (LPD), measured in watts per square foot, for various building or space types. In other words, the amount of power you can draw with every light in the building turned on at full output – but it is the rare building that has every light turned on 24/7.
Energy = Power x Time, so an energy code needs to take power (watts) and time into consideration. This is why we pay for electrical energy by the kilowatt-hour (energy), not by just the total wattage of all the devices connected to the meter (power). To be fair, current energy codes do have provisions that address the time variable of the equation – but they only do it by requiring automatic controls to shut off the lights when not needed. There is no quantification or metric of what those controls get you in energy use reduction. A building with lights on 20 hours per day is treated the same by code as a building with lights on 10 hours per day. A building with the most rudimentary code-minimum controls is seen as identical to a building with sophisticated occupant-sensing and daylight-responsive controls.
We can see why lighting power as the metric for building lighting energy-efficiency is deficient, but is this a big problem? Yes, and here is why: energy use of our buildings must be reduced radically – the push to do that by improving the performance of envelope, HVAC, and lighting is strong and growing stronger, and rightfully so. For example, the energy bill working its way through Congress, at 1,000-plus pages, contains a section to institute energy codes enforceable at the Federal level with a target of 55% energy reduction (over the 2004 code baseline) by 2018, and 75% by 2030. Serious stuff! So when looking at lighting, the obvious thing is to just keep reducing the lighting power allowances, right? Wrong! The use of more efficient lamp and fixture technologies alone can’t achieve these targets. If we just keep pushing down power allowances, lighting quality will suffer and we will find ourselves sitting in dark rooms or bland white rooms lighted with bare, glary light bulbs. To truly reduce lighting energy use we need to figure out a way to write a code that actually regulates lighting energy, not lighting power.
Photo Credit: Isaac Bowen