LEDs (light emitting diodes) are solid-state lighting devices that produce light when a forward voltage is applied. An LED consists of a semiconductor diode packaged in a clear epoxy or silicon gel. The diode contains two slightly different materials: a P-type semiconductor and an N-type semiconductor. The P-type semiconductor has “holes” created by a lack of electrons, producing a positive charge. Conversely, the N-type material has an excess of electrons, resulting in a negative charge. The P- and N-type semiconductors are placed in direct contact in the diode and the region where they meet is referred to as the PN junction. When an electric current passes through the device, electrons flow toward the P region and holes flow toward the N region. Near the PN junction, electrons and holes combine and the electrons shed the extra energy they acquired from the electric current. This energy is released in the form of a photon, the basic unit of light. In this way, an LED emits visible light.
The energy of the photons corresponds to the color of the light emitted. In the visible light spectrum, blue and purple light results from the greatest energy emission whereas yellow and red light is a result of the lowest energy emission. By utilizing materials with different band gaps, engineers can alter energy emission and thus the color of light produced by an LED.
Unlike other lighting technologies, solid state (LED) lighting as an emerging technology in the general lighting industry is just at its beginning – a kind of new frontier. As the industry continues to evolve and mature, LED lighting brings with it a bright future. But, until the future arrives, we live in the Wild West where there are few rules, few standards, and little enforcement within the industry. Many luminaire manufacturers have emerged with LED lighting products trying to stake a claim. Some are dedicated to furthering LED lighting’s future while many are just trying to cash-in. Until law and order becomes the norm, consumers are left with the difficult challenge of trying to determine which products are best suited for their applications.
To complicate matters, choosing the right LED lighting product is akin to buying an automobile which comes in all shapes and sizes and performs differently in various environments. Like the automobile, LED lighting is a complex system with many options and features that are chosen to fit differing applications. There is no “one size fits all” product. Consumers have many criteria to consider when selecting the right LED system.