Light Emitting Diodes

Incandescent Bulbs

100-year-old Inefficient Light Technology

Incandescent bulbs use a 100-year-old technology that generates light by passing a large amount of electrical current through a small wire. This wire glows white-hot (almost) and radiates energy in all directions. A consequence of this method of generating light is that only 15% of the energy produced is visible light; the remaining 85% is dissipated as heat!

Out of the rainbow of colors that make up white light, you have to filter out all of the light, except the color you want the lantern to emit (i.e., a blue lens blocks or filters out all light except blue). In the end, very little of the energy emitted by the incandescent lamp is seen by the observer through the colored filter.

As illustrated above, for filtered interior incandescent bulbs, the intensity depends on the color. For blue, the filtered transmission is about 0.4%, for green, about 1%, and for red, about 1.5%. The rest of the energy is wasted in heat dissipation.

Compact Fluorescent Lamps

Convenient, but Fragile, Complex and Environmentally Hazardous

Compact fluorescent lamps (CFLs) were developed as a relatively efficient alternative to incandescent bulbs and many solar-powered outdoor lighting products utilize these lamps as their light source.

In short, fluorescent lamp technology consists of a thin glass tube filled with argon/mercury vapor. At each end of the tube are metal electrodes coated with an alkaline-earth oxide that gives off electrons easily. When a current is passed through the ionized gas between the electrodes, the fluorescent lamp emits ultraviolet radiation. The inside surface of the fluorescent tube is coated with phosphors, typically zinc silicate or magnesium tungstate. These phosphors absorb the ultraviolet radiation and re-radiate the energy as visible light. A fluorescent lamp will operate until the alkaline-earth oxide coating on its electrodes is depleted.

When starting a fluorescent lamp, the unit requires a "boost" in the form of a starter and ballast that provide up to four times the operating voltage in the beginning.

Disadvantages of CFLs:

• Unfocused illumination. Similar to incandescent bulbs, CFLs create unfocused light, and produce an uneven illumination. To compensate, systems using fluorescent lamps typically install reflectors to redistribute the output, which is inefficient and creates an additional level of complexity and cost to the product.

• High energy consumption. CFLs can consume up to 20 watts, depending on their application (although the tubes are listed at a lower wattage, it is important to consider that the driving ballasts use energy as well). This level of power consumption requires large, expensive solar modules and associated installation hardware to generate the required energy. In addition, large batteries are required for power storage and typical reserves are less than a week - this doesn't leave enough autonomy to compensate for seasonal or poor climatic conditions.

• Difficult to power manage. CFLs tend to be either "on" or quot;off". Although it is not impossible to adjust the output dynamically, it is a complicated process. This makes power management difficult, imprecise, or non-existant, which is a liability for solar-powered lighting products where the source of power varies according to seasonal fluctuations and prevailing weather conditions.

• Short operational life. The rated life of typical CFLs is about a year and products using them require regular maintenance. This increases the life cycle cost of the product in terms of servicing labor, storage costs and proper disposal (fluorescent tubes and their ballasts are considered hazardous materials).

• Temperature degradation. Manufacturers of CFLs conduct their rated life and light output calculations under ideal operating conditions and temperatures that usually do not reflect the actual environmental conditions. The performance and lifespan of CFLs is dramatically degraded by extremes in ambient temperature.

• Fragility. Another drawback with CFLs is that they are composed of fragile glass tubing. If the fixture is impacted with minimal force, the tube will break and the lamp will cease to operate. Moreover, the resulting glass fragments are sharp and dangerous.

• Hazardous materials.The EPA in the United States regulates the disposal of CFLs because of they contain highly toxic mercury. The ballasts are also regulated under the Toxic Substance Control Act (TSCA) and Comprehensive Environmental Response Compensation and Liability Act (CERCLA) because they contain PCB's and other toxic components.

LEDs

Efficient, State-of-the-Art Light Technology

At the heart of a Light Emitting Diode (LED) lamp is a silicon "chip" about the size of a grain of salt and made of a special blend of crystals. When a small electrical current is passed through the chip it generates light.

LEDs offer a number of technical advantages over any other type of lighting, including:

• The color of the light produced by LEDs is dependent on the combination of crystal materials that comprise the silicon chip. Therefore, LEDs produce only one color, as needed, for a particular light application. Almost all the energy required by the LED is usable as the intended color without the need for filters. Currently, LEDs are available in white, amber, red, green and blue output colors.

• Unlike incandescent bulbs or even fluorescent lamps, almost all of the energy used by LEDs is converted to light, rather than heat.
  

  As the examples in the graph above indicate, the luminous efficiency for an LED ranges from about 5% for blue to just over 20% for red, and almost no energy is wasted through heat dissipation.

• Furthermore, the shape of the LED package focuses the light without the need for additional optical components, making them more efficient and cost-effective at utilizing the light produced. The isotropic nature of incandescent or fluorescent lamps requires external optics to collect the emitted light and direct it in a usable fashion.

• The combination of these effects makes LEDs many times more efficient at producing light than incandescent bulbs or fluorescent lamps. In addition, the lifetime of an LED is about 100,000 hours (27 years assuming the LED is on continuously for 10 hours per day); this is about 20 times as long as the best incandescent bulbs (5,000 hours) and twice as long as the best fluorescent lamps (cold cathode CFLs are rated at about 50,000 hours).

• LEDs are extremely durable. Vibration or shock easily breaks the fragile filament in an incandescent bulb and the glass tubing of a fluorescent lamp. LEDs, on the other hand, are completely solid-state technology and are virtually indestructible!