There are many types of LED resistors, and they are categorized by the color of their light or the number of colors of light they produce. Many people think the color of the plastic housing on an LED resistor determines the type of LED light, but the color is actually a result of the wavelength of light emitted when a semiconductor metal is electrically excited. Most LEDs produce only one color of light, but some types offer two colors — bi-color — or three colors — tri-color — in a single LED package and can turn on one or more colors at the same time. Many types of LEDs are used in lighting situations that benefit from low power, long life, or bright light from very small bulbs.
LED resistors come in a rainbow of colors, including red, orange, yellow, green, blue, violet, and purple, as well as infrared, ultraviolet, and white. Blue and white LED resistors are a relatively newer type of LED and are typically more expensive. Different types of LED resistors have different kinds of metals inside. For example, aluminum gallium arsenide — a compound of aluminum, gallium, and arsenic — glows red in red LEDs while gallium arsenide phosphide — a compound of gallium, arsenic, and phosphorus — glows orange to produce orange LEDs. Zinc selenide, a compound of zinc and selenium, is used in blue LED resistors.
Some of the advantages of LED bulbs are their low power requirements, long service life, and bright light. Low LED power requirements make LED resistors ideal for use in battery-operated devices that produce bright light, including the LED displays in cell phones, presentation pointers, keychain lights, LED flashlights, and LED headlamps. LED flashlights can perform longer without battery replacement, using significantly smaller, lighter batteries such as two AA batteries, instead of traditional incandescent flashlights that require two or more heavy, D-size batteries.
In addition to low power requirements, long service life makes LED lights ideal for lighting where replacing bulbs more often would be expensive or might result in safety problems. That’s why large numbers of LED resistors are often massed together to provide light in traffic signals, car turn signals, and aviation lighting. Because low power requirements would also be an advantage in the home, LED room lighting may become popular as the technology improves and prices drop.
All types of LED resistors are light-emitting diodes that glow when current flows through them in the forward direction. An LED circuit must be wired with the LED resistor in the correct orientation. The anode, the longer of the two wires going into the LED packaging, needs to be connected to the positive side of the battery or power supply. The shorter of the two wires on an LED, the cathode, needs to be connected to the negative side of the battery or power supply. Another way to identify the cathode is that, on a round LED, one side will usually be slightly flattened; that’s the cathode.