120 VAC Lighting & Inverters by Richard Perez Regular AC lighting devices are the most commonly used. These devices vary greatly in efficiency. Most homes, even AE homes, are required by building codes to be wired for 120 VAC. This article concentrates on getting the best values in 120 VAC lighting appliances when powered by the batteries and inverters used in home style AE systems. So Why Use the Inverter? Lighting devices are prime candidates for inverter supplied electricity. Lights spend an average of over 4 hours per day operating. They generally consume just a few hundred (or less) Watts of power. Running a 120 VAC power source is just not practical for such low powered and continually used appliances. If you are not using 12 VDC for your lighting, then your only other easy choice is 120 VAC. Since most AE sources are low voltage DC, the inverter is necessary to convert the low voltage DC to 120 VAC. The use of the inverter for lighting also has another advantage. Most already existing homes are not wired to accept 12 VDC. If you consider the cost of retrofitting a home for low voltage wiring, then the use of standard 120 VAC lighting devices and an inverter is a reasonable and cost effective alternative. The inverter allows usage of the already existing wiring and fixtures without modification. This saves considerable money in comparison with a complete rewire job requiring destruction of the walls and installation of specialized wiring. In general, if you are building a new AE powered structure, it is more cost effective to wire the structure for 12 VDC lighting. If you are dealing with a structure that is already constructed and wired for 120 VAC, then using an inverter and the already installed lighting fixtures is much less expensive than ripping apart the walls and installing new wiring. Incandescent vs. Fluorescent Once you have decided to use 120 VAC for your lighting, then the next choice is whether to use incandescent or fluorescent lighting. The situation here is the same as we discussed in the lighting article in Home Power #1. Fluorescent lighting offers you the same light at about the quarter the cost of incandescent devices. This is true even if the higher initial cost of the fluorescent fixture is considered. The primary cost of lighting in alternative energy homes is not the lighting fixtures or the bulbs, but the energy it takes to power the lights. As AE users, we pay many times the cost of utility produced electrical power. It pays us to buy efficient appliances even though they may be initially more expensive to purchase. What really counts is where you put it... Regardless of the type (or voltage) of lighting you choose, the technique for efficient application remains the same. If you want to save on energy used for lighting the first thing to think about is the position and size of the light. Spot lighting, especially in work areas such as kitchens, desks, and work benches, is most effective. Spot lighting focuses the light where it is needed. This allows usage of lower wattage lights while still maintaining acceptable illumination where it is needed. The idea is really quite simple. Consider sitting at a desk and reading a book. We could use a 40 watt incandescent desk lamp at a distance of say 1.5 feet from the book for illumination. Or we could use 440 watts worth of light bulbs on the ceiling, some 5 feet above the desk, to provide the SAME AMOUNT of light on the book. That's over ten times the energy being consumed to provide the same illumination on the book laying on the desk. Light is radiant energy, and as such, obeys the inverse square law of radiation. This means that every time you double your distance from a light source, the intensity of the light is divided by four. So give your AE system a break and use spot lighting wherever possible. Locate all sources of light as close as possible to where they are needed. It is much more efficient to place several smaller spot lights around a room for illumination than it is to use a single large light source on the ceiling. I like to think of this concept as "The Moving Light". The idea is to have several low intensity (thereby low wattage) light sources around a room wherever they are needed. There are only one or two of these lights burning at a time. Where are they burning? They are burning WHERE YOU ARE. The light follows you around the room because you switch off the light in an area when you move to another. The Moving Light. You save energy by not illuminating areas that don't need light. This idea is a corollary of the ancient American Indian proverb, "White man build big fire stand back; Indian build small fire, sit on top."-- Indian Tom via George F. Wright, Agate Flat OR. In some cases area lighting is desirable. Most area lighting fixtures are designed with shades, valences and other light diffusers/reflectors. These are designed to prevent the relatively intense (high wattage) light from directly striking our eyes. This technique, while interior designer approved, wastes a hell of a lot of energy. If you are using area lighting dispense with valences and diffusers and use lower wattage lighting units. The best place for area lighting is the ceiling in the center of the room. Use area lighting minimally, only as an occasional supplement to spot lighting in areas of interest and activity. If you use area lighting, with its high intensity requirements, install fluorescent types for their high efficiency. So the most important factor in any lighting system, whether 12 VDC or 120 VAC, is the sizing and positioning of the fixtures. Put the light where you need it, keep the wattage down, and turn it off when you don't need it. Do these three things and you'll save energy. Incandescent Light Bulbs & Inverters Incandescent lightbulbs are perfectly happy when powered by inverter produced electricity. These lightbulbs are resistive loads to the inverter, and even the crudest inverter can handle them with ease. When computing the wattage consumed by an incandescent lightbulb powered via inverter be sure to add an additional 10% for the inverter's inefficiency. The incandescent lightbulb itself is an efficiency engineer's nightmare. Over 90% of the electrical energy we put into the bulb is wasted as heat, with only about 6% being converted to usable light. This very low efficiency means that we should keep the wattage of our incandescent bulbs as low as possible. Experiment with your incandescent bulbs. If you've been using a 75 watt bulb in a lamp, then try a 60 watt or 40 watt bulb. You may find that the lower light intensity is perfectly acceptable. The human eye automatically adjusts itself to the amount of light available. Provide too much light and the eye's pupil contracts and lets less light into the eye. Fluorescent Lights on the Inverter Fluorescent lights are inductive loads to the inverter. This means that their usage with inverters is subject to certain vagaries, or what engineers call "glitches". Inverter manufacturers are attempting to provide a reasonable facsimile of conventional 60 cycle sinusoidal electricity coupled with high inverter efficiency. In fact, all square wave and modified sine wave inverters offer only an approximation of sinusoidal energy. The energy they produce is not IDENTICAL with commercial electricity. How close this approximation is varies very widely from inverter to inverter. Some types will power fluorescent lighting with no problems, while others will not. From personal experiences we have determined that the following three inverter makes will power most standard fluorescent lighting: Trace, Heliotrope and Heart. Depending on the type of fluorescent and inverter used the light may buzz during operation. Well, in fact all fluorescent lights, even those operated on the grid, buzz somewhat. With some inverters this buzz can be loud enough to be annoying. The three inverters mentioned above provide the minimum amount of noise at the light. The best type of fluorescent we have found for quiet inverter operation are the rapid start ballastless types. We also prefer the warm white type of fluorescent tube for its more frequency balanced light. The electronic ballast used in many fluorescent fixtures is designed for sinusoidal power input. It is not designed for the modified sine wave power output of today's super efficient inverters. Standard fluorescent ballasts will run hotter, be less efficient, and shorter lived when used on inverter produced electricity. This is one more reason to use the rapid start ballastless type of fluorescent lamps. They are not only quieter, but also more efficient and longer lived. Several readers of Home Power have written to us mentioning potential health hazards involved in fluorescent lighting. To date, I have yet to see any hard scientific evidence that supports these claims. While I am not particularly a fan of the light produced by fluorescents (its not balanced in frequency output and hard on my eyes), I use them because they are so efficient at their job. If anyone has any real evidence supporting the claim that fluorescent light is damaging to our health, then please write us. We'll print this information if it is scientifically supported. In summation, the prime reason to use 120 VAC lighting in AE systems is to use already existing wiring and fixtures. Those considering building a new AE home should consider dual lighting systems, both 12 VDC and 120 VAC. This offers maximum efficiency and flexibility. The most efficient form of lighting is spot lighting rather than area lighting, regardless of voltage or lighting type. The most efficient type of commonly available 120 VAC lighting is the fluorescent. So give your system's lighting a second glance and save some energy!