Types of LEDs
Traditional LEDs are usually available in 3mm, 5mm, and 10mm which denotes the size of the LED in diameter. These older types of LEDs are typically used where size and brightness are not as important, such as indicator lights or automotive gauges. Traditional LEDs usually have a rounded half-circle top, which focuses the light forward. This is sometimes called "bullet" or "normal". They are also available with a flat top, which disperses the light forward. Finally, they are available in an inverted design, which disperses the light in all directions. The LED design varies by the application, since each design has a different light output effect. To make it easier to identify them, many manufacturers use colored bulb bases whenever possible. These traditional LEDs last a long time, but are prone to failure when too little or too much power is used. They are also the least bright type of LED, and have been replaced with newer technologies for most applications.
Suface-mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto the surface of the printed circuit boards (PCBs). The electronic device produced in this method is called a suface-mount device (SMD). In the industry, SMT has largely replaced the through-hole technology construction method of fitting components with wire leads into holes in the circuit board. An SMT component is usually smaller than its through-hole counterpart; the anodes and cathodes are completely flat. A difference in SMD LEDs versus standard ones is the number of light sources, sometimes called "chips". The highest quality is 3-chip, for which there are 3 anodes and 3 cathodes on each individual SMD chip. Effectively, each 3-chip LED is actually 3 LEDs, in one "package."
These SMD LEDs have quickly replaced traditional LEDs in almost every automotive bulb application, due to their smaller size in relation to the amount of light output. Similar to traditional LED-bulbs, most manufacturers use a colored bulb base to more-easily identify the color of the bulb. SMD LEDs last a very long time, but are prone to failure if too little or too much power is used, and they require a higher level of construction quality in order to ensure all soldering is perfect- since the connection points on the LED are much smaller, it's much easier to make a mistake compared with older LEDs. As they are higher in brightness, SMD LEDs also produce more heat in operation, requiring proper design to ensure longevity.
The newest type of LEDs are known as high-power LEDs. These LEDs are the same technology as an SMD type LED, but are thicker, allowing for greater current, and more light. These are usually described in terms of the maximum power dissipation, in watts. These chips can vary in size and shape. Commonly, high-power LEDs will be referred to as "Cree" LEDs, as Cree, Inc., a U.S. manufacturer of LED chips, was the first company to make high-power LEDs widely available. Now, all high-power LEDs that use the general design are known as Cree LEDs, but be aware that there are many suppliers that describe their bulbs as "Cree" but do not actually use the highest-quality, genuine Cree-brand chips.
By combining different high-power LED chips of varying sizes, the overall bulb is rated by the total power rating. For example, the 11W bulb uses four 1.5W chips and one 5W chip, for a total of 11W. With the proper and correct design, hi-power LEDs can last for a very long time. However, the bulbs produce more heat than any other type of LED, so the design is critical to prevent overheating. Usually these LEDs use aluminum housings for heat dissipation.
For more information on the design of LEDs, visit our LED Design page.