Let There Be Light by Alan Trautman & Richard Perez Welcome to the first column about appliances and alternative energy systems. In the coming months we will be discussing a myriad of appliances and their application in alternative energy systems. From refrigeration to TVs, stereos to vacuum cleaners, we will cover it all, both AC and DC. The emphasis in this column will be on what is efficient, works and is cost effective. We are going to start with probably the most useful appliance Man has ever developed, the appliance that turns night into day--Lighting. Lighting is not only Man's first appliance, it is the most common. Lighting appliances are one of the prime reason to invite electricity into your household. In time past, men used to huddle around the campfire for its light and warmth. As technology developed man burned a variety of fuels to produce light. This worked OK, but was smelly, dim, and dangerous. In modern times, man has used the most versatile form of energy to make his light-- electricity. This article is a discussion of lighting devices for use in alternative energy systems. Here we are primarily concerned with getting our lighting chores effectively done with the minimum energy expenditure. Lighting can be accomplished in alternative energy systems in two ways-- low voltage DC, or 120 VAC through the inverter. In this article we will limit ourselves to 12 VDC lighting. Tune in next month for a discussion on 120 VAC lighting via the inverter. In the world of 12 VDC lighting, we basically have two choices-- incandescent or fluorescent lighting devices. Let's examine the incandescent 12 VDC lamps first. The fine and wonderous selection of 12 VDC incandescent lights come to alternative energy systems from their very close electrical cousins, the automobile and the recreational vehicle. Automotive lamps offer the alternative energy user a wide selection of lights. Everything from very dim to superbright is available, and it all consumes 12 VDC directly from the battery. In general, small auto lamps produce between 50 and 400 lumens. The Lumen is a scientific standard for measuring the visible light intensity. For reference, a standard 23 Watt automotive stop light produces about 400 lumens of light output. The incandescent lamp emits light because the electronic motion through its filament heats the filament to a white hot state-- it incandesces and gives off light. The main problem with heating materials to incandescense for light production is inefficiency. Most incandescent lighting is less than 10% efficient. In other words, 90% of the input energy to the incandescent light makes heat rather than visible light. Table 1 is a spreadsheet showing the operating characteristics of a variety of small automotive incandescent lamps. This table is arranged with the higher light output lamps first. All lamps are named with their automotive identification number. Note that this table gives us several types of information about these lamps. The lamp's wattage (input power consumption), light output in Lumens, efficiency in Lumens per Watt, longevity (in operating hours), cost, and information about the cost of operating the lamp. The information related to operating cost comes in two forms--dollars per 1,000 hours of operation, and dollars per Lumen per 1,000 hours of operation. One thousand hours of operation is roughly equivalent to about a year's use. The figures relating to cost all take the lamps longevity into account. For example, if the bulb is rated to last 200 hours, then we assume that five bulbs will be used during the 1,000 hour period. These cost operating figures point out some interesting information about using incandescent bulbs. The purchase cost of these lamps is insignificant compared to the cost of the power it takes to run them. Most alternative energy systems produce their electrical power at between $0.65 and $1.75 per kiloWatt-hour. Since this is much greater than the $.07 per kiloWatt-hour that the commercial grids charge, one must be aware of the great importance of efficiency. We have used the power cost at $1.00 per kiloWatt-hour as our standard, and this cost reflects an average for most small alternative energy systems. Note that a 1073 car stop light bulb produces 402 Lumens of light, while consuming some 23 Watts of power to produce this light. This means that the light costs $.07 per lumen per 1,000 hours of operation. It costs the alternative energy user $28. to power and buy one of these lamps for 1,000 hours of lighting. This includes both the cost of five lamps (the 1073 has a lifetime of 200 hours), and the energy to power the lamp over the 1,000 hour period. The 1073 is relatively efficient as incandescent lamps go. It produces about 17.45 Lumens per Watt of input energy. What Table 1 tells us is that the automotive incandescent lamps are more efficient the larger light output they produce. Look at the table and see what we mean. The 1073 outputs 402 Lumens at 17.45 Lumens per Watt, while the smaller 89 bulb produces 75 Lumens at 10 Lumens per Watt. This is standard for all car bulbs, the larger they are, the more efficient they are. The larger they are, the more overall power they also consume. So, the alternative energy user is present with some minimum-maximum type choices. It is a situation of balancing the amount light you need with the amount of power you wish to consume. Note that although the smaller bulbs are less efficient, they cost less to operate over a 1,000 hour period. They also put out less light, and this is the reason that they are cheaper to operate. If you are considering using 12 VDC automotive bulbs in your system, then use this simple rule of thumb to select your bulbs. First of all, consider the amount of light you need for a particular job. The 400+ Lumen lamps are more than adequate for reading or close work when located within 5 feet of the area being viewed. The smaller sizes may also be adequate if located closer to the work. In alternative energy systems, it is not practical to use large area incandescent lighting. Instead, place the light as close as possible to where it is needed. If area lighting is used at all, it should be of a more efficient type than incandescent lamps. After you have determined the amount of light you require, then browse through the table until you find the one that offers the lowest operating cost over a 1,000 hour period. For example, let's say that we need a reading lamp with some 200+ Lumens of light output. The table gives us six choices of bulbs to use. The number 1141 bulb can deliver the light at the lowest operating cost, some $20. per 1,000 hours of light. Note that the 1141 has a rated lifetime of 500 hours, so you'll use up two of them within the 1,000 hour period. One of the major advantages of automotive bulbs is their availability. They are everywhere. Their fixtures can be purchased from RV stores, or you can scrounge sockets for them from automotive junk yards. Consider the two filament bulbs, like the 1034, used in car tail lights. The high output filament is the stop/directional signal lamp, while the low output filament is the running/tail light. The socket for this bulb can be had inexpensively at just about any junkyard or auto parts store. If both filaments are wired to a two position switch, the user can select either high or low lighting to suit his immediate need. Your usage of automotive incandescent lamps is limited only by your imagination. So have fun, make a trip to the junkyard or RV supply and see what you can dig up. Remember, if it works in a car or RV, then it will work on your 12 VDC battery system. Incandescent lighting is bright and initially cheap, but alas, it is also very inefficient. Considering the expense of electrical power in alternative energy systems, it is more cost effective to use more efficient types of lighting. Fluorescent lighting is the next step. For the same light output, fluorescent lighting averages over 4 times more energy efficiency than is incandescent lighting. Again refer to Table 1. Note that the fluorescent lamps have much greater efficiencies (Lumens/Watt) than the incandescent types. This is due to the physical principles behind the fluorescent's operation. While the incandescent lamp makes light via heat, the fluorescent does not use heat to make its light. Instead, fluorescent particles within the lamp are stimulated into light emission by excitation with high voltage electrons. This process is much more efficient and has only minimal losses as heat. The fluorescent lamp does require high voltage in order to operate. This means that if the lamp is to be powered by low voltage DC, then a mirco-inverter must be used. This micro-inverter is a miniaturized electronic inverter which steps the 12 VDC (from the battery) up to the 100+ volts required to drive the fluorescent tube. The micro-inverter is located within the light fixture, where it presents no hazard to users. The cost of the micro-inverter is the principle reason why the 12 VDC fluorescent lamps cost more that their 120 VAC cousins. Note that Table 1 gives us a choice of many different intensity fluorescent lamps. Some of these tubes are very bright, and these are the type to consider for area lighting. Only the fluorescent lamps have great enough efficiency to be used in large area illumination. If you are screwing it to the ceiling, then it had better be fluorescent. The cost of operation of these lamps is much lower than incandescent lamps. Cost analysis of fluorescent lamp usage is not as simple as that for incandescent lamps. The fluorescent fixture has a much higher initial cost. We have based our calculations on a fixture lifetime of 7.5 years. This is about what we are personally experiencing. Most fluorescent tubes are rated with lifetimes in the several thousands of hours. However, our personal experiences show us that about 1,000 hours is an average lifetime for a tube run on micro-inverters. So, all cost calculations relating to the fluorescent lamps are based on a fixture life of 7.5 years and a bulb life of 1,000 hours. Let's compare the operation cost of two light sources, the 1073 incandescent bulb, and the F8T5/CW fluorescent tube. Both these light sources put out about 400 lumens of light. The 1073 lamp consumes 23 Watts, while the F8T5/CW tube consumes 10.24 Watts. That's right, the fluorescent tube produces the same amount of light with about half the energy consumption. In terms of operating cost over a 1,000 hour period, the F8T5/CW fluorescent costs $19.07, while the 1073 lamp costs $28.09. Even considering the initially higher cost of the fluorescent lamp and its fixture, its greater efficiency makes it pay for itself by reduced power consumption. The story is about the same for other incandescent versus fluorescent lamps, the fluorescent saves us money every time. Consult Table 1, the fluorescents average $.03 per Lumen per 1000 hours of operation, while incandescents average $.12 per Lumen per 1000 hours of operation. The Bottom Line is that the fluorescents are a FOUR TIMES better deal for your lighting dollar than are the incandescents! Low voltage fluorescent lighting is manufactured by a variety of companies. Don't be mislead by shopping strictly by cost. The quality of the micro-inverters and fittings in the lights varies greatly from type to type. High quality 12 VDC fluorescent lights will cost you about $30 to $50 each. Such lighting will last for years and will be warranteed for 2 years or more. It will be quiet and will not interfere with your radios and TVs. Our cost estimates here are based on high quality lighting. Don't waste your money on poorly designed and cheaply made 12 VDC fluorescents. These will fail rapidly, interfere with electronics, and are not cost effective. In conclusion, if 12 VDC is used to directly power lighting, we have two basic choices-- incandescent or fluorescent. Incandescent lighting is initially cheap, but expensive to operate because of its inefficiency. Fluorescent lighting requires a higher initial investment, but quickly pays for itself by saving energy. In general, we recommend using fluorescent light wherever possible, and especially in all lights that operate an hour or more daily. Next Month, 120 VAC lighting powered by inverters.