Lighting technology
Lighting technology has advanced rapidly in the past decade thanks to new innovations in LED technology in Lighting. LEDs, short for Light-Emitting Diodes, have seen widespread use since their commercial introduction nearly six decades ago as simple indicator lights for items such as control panels, stereos and various other types of electronic equipment. Today, LEDs have progressed to the point where they are fulfilling some of the most demanding lighting applications on the planet.
While the basic concept behind the technology is similar to that of most other lighting types, there are significant differences in how LED technology operates compared to all other lighting types. Understanding these differences is important when shopping for LED lighting options, especially for those who are replacing existing traditional fixtures such as those using fluorescent, HIDs and incandescent technologies.
LED's Works
As mentioned previously, Light-Emitting Diodes work along the same basic concept as traditional lighting sources – they generate light by electrical current flowing through them. This is where the similarities end however. Unlike traditional lighting sources which rely on heat or a chemical reaction in order to produce illumination, LEDs rely on a semiconductor for their light source. This is a unique technology that offers significant technological benefits and far greater potential for continuous advancement.
To explain how LEDs work, it is important to first understand what a semiconductor is and how it functions. Semiconductors are materials with varying ability to conduct electrical current. Light-emitting diodes are some of the simplest types of semiconductor in existence. Most semiconductors have impurities added to them in order to allow electrons to flow through, since on their own pure semiconductor material is a poor conductor. When a semiconductor has impurities added, this is referred to as doping.
Generally speaking, these semiconductors are made of aluminum-gallium-arsenide (AlGaAs). When this material is doped, it can either add free electrons or create holes in the material where electrons can go. When a semiconductor has extra electrons, it is known as an N-type material since it has extra negatively charged particles. When there are extra holes in the semiconductor, it is known as a P-type material since it effectively has extra positively charged particles.
The basic construction of a diode consists of a section of N-type and P-type material bonded together with electrodes on each end. In this arrangement, electricity is only conducted in a single direction. With no voltage applied, a depletion zone is created between the P and N type materials, restoring the semiconductor to its original insulating state where no electrons or electricity can flow.
In order for the depletion zone to be removed, electrons must be moved from the N-type area to the P-type area, as well as the holes in the reverse direction. Once this occurs through a significant enough voltage, the depletion zone is removed and the charge moves across the diode. It is this interaction between the electrons and holes that generates the light seen in an LED. Specifically, the light generated by an LED is actually a result of the release of photons from the movement of these electrons from one orbital of an atom to another. The greater the distance between orbitals, the greater the energy released by an electron during the interaction and the higher the frequency of light produced. Inversely, the shorter the distance between orbitals, the lower the energy released during the interaction and the lower the frequency. Lower frequencies are often in the infrared portion of the light spectrum which means it is invisible to the human eye.
This variability in an electron’s orbital change is responsible for the wide range of color temperature options available in LED lighting today. Compared to traditional lighting with fixed or restricted color temperatures, LED,s offer a nearly endless range of possibilities for every type of bulb. In fact, certain LED fixtures offer the option for the user to easily switch between different color temperatures.
Overall Construction
Outside of the semiconductor diode, there are several other key components of an LED that are required in order for it to function. These include the leadframe made up of the post and anvil, the reflective cavity, wire bond and the epoxy lens or case. Certain LED designs may include additional parts or have further sophistication, but all contain these basic parts. Below is a detailed list of each of these components.
Leadframe – Outside of the semiconductor die, the leadframe is the heart of an LED chip. This consists of an anvil, which is negatively charged and holds the semiconductor material itself, and the post, which is positively charged and contains the wire bond which provides current into the die. These two components of the leadframe do not physically touch, and are only connected via the wire bond.
Reflective Cavity – This is a reflective material that surrounds the semiconductor die, directing all light outwards towards the lens. It is usually many times larger than the die itself.
Wire Bond – This is the tiny filament of wire that runs from the post to the center of the semiconductor die, providing it current.
Epoxy Lens/Case – This provides protection and structural stability to the LED unit, rigidly affixing all components in place. It offers a degree of impact protection, as well as significant vibration resistance, which is critical for industrial or high performance applications.
Sub-Types
All Light-Emitting Diodes are built on the same basic principle and components. However, there are some significant differences in the design between these different technologies, which are detailed in the following diagrams.
Standard Diode – This is the most basic form of LED, and also the oldest. It involves a relatively straightforward circuit consisting of an anvil and a post, with a wire bond electrically connecting the post to the semiconductor material in the anvil. All of these components are encased in an epoxy resin lens/housing, with anode and cathode connections ready for easy soldering to a board.
SMD LED – Short for “Surface Mount Device”, these LEDs are unique in that instead of being individual parts that are manually soldered to a board, they are actually mounted onto the board itself. One of the biggest advantages of this design is that the LED mount acts as a heat sink, allowing higher current flow and higher efficiency, generating more light.
