Lighting is one of the most popular applications for solar power, whether it be for small home systems or city street lights. But light is difficult to sell because it is poorly understood and hard to measure. Our eyes adjust to available light levels, so our perception of “bright” is constantly changing. It is also difficult to compare lights based on their wattage. For example, people frequently ask for a “250 watt solar street light”. In this case, the wattage (250) doesn’t tell us anything about how much light is required. Similar light levels might be attained by using a much more efficient lamp that consumes 60 watts, for example.
In general, solar lights are not as bright as AC lights – partly because their power consumption is much less and partly because they are designed so that they do not waste as much light. This can become a problem where both AC and solar lights are installed close to each other. The human eye adjusts to the brighter AC light, making the solar lights appear very dim. Check this article out Economist article for an interesting view on the subject.
One of the most popular solar light technologies is compact fluorescent (CFL) lamps, also called “energy saving” lights. These lights are widely used for AC lighting, but are also available in 12v for direct solar applications from a 12v battery. CFL lights use electric current to excite gas inside the lamp, which makes the lamp glow. Every CFL also has a ballast which converts the input voltage to the correct voltage to “fire” the lamp. Remember that AC lamps have a ballast meant for AC voltages, and they should not be confused with 12vdc lamps.
The most fashionable form of lighting today seems to be LEDs (light emitting diodes). These are solid state devices that send current across a diode to make a bright, piercing light. One of the challenges with LEDs is dispersing or diffusing the light across a wide area. Although many manufacturers have entered the LED business, we have found that many make unreliable or ineffective lights. After much experience, we only use one manufacturer for our LED street and area lights because we believe they have addressed many of the issues relating to temperature, diffusion and voltage.