R Classroom | Types of LEDs

Latest update time：2024-10-16

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Key Takeaways from this Article

・ LED packages can be roughly divided into two types: surface mount (chip) type and lamp type.

・ Packaging can protect light-emitting components, control the direction of light, adjust the color of light emission, and make soldering and mounting easier.

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Types of LEDs

LEDs are widely used in our lives. In addition to being used as lighting, switches, sensors and backlight sources, they can also be used for outdoor displays and street lights, as well as special purposes such as automobiles, medical treatment and agriculture. Users can use LEDs of different shapes and wavelengths according to application requirements. This article will introduce the types of LEDs and the characteristics of each type of LED.

LED packaging

LEDs can be roughly divided into the following two types according to their shape

① Lamp type LED

Dome-shaped LEDs are also commonly referred to as "Lamp-LEDs". This is a representative package form that has existed for a long time. There are a variety of package sizes, with 3mm and 5mm diameters being the main sizes. The outer layer resin includes three types: colorless and transparent, colored and transparent, and colored scattering. The scattering type is mainly used for applications that require a larger viewing angle, and the colorless and transparent type is mainly used for applications where you want to prevent the color of the light from being seen when the light is off. In addition to the shell-shaped resin, there are other shapes such as square and cylindrical.

Installation method: Lamp type: pass the pins through the holes (through holes) on the circuit board and solder (dip soldering)

② Surface Mount Device (SMD) LED

The LED that encloses the light-emitting element in a surface-mountable package is generally called a "chip LED". There are molded types and reflective types with a reflector installed in the package. This type of LED can save space and achieve wide-area lighting.

Installation method: Surface mount type: solder the pins of the patch directly to the surface of the circuit board (reflow soldering)

Most SMD LEDs emit light from the top, but there are other types such as side view types that emit light from the side, and back view types that are mounted on the underside (back side) of the circuit board. These are suitable for applications where you want to save space when installing and illuminate in every direction.

In terms of size, ROHM can provide a wide range of products from ultra-small size 1006 (1.0×0.6mm) to high-power size 4520 (4.5×2.0mm), and customers can freely choose according to application requirements.

Two-color and three-color luminescence

Another type is to integrate multiple light-emitting elements into one LED package to emit two or three colors of light. This product can light up one color at a time, or mix colors by emitting several colors at the same time to form various colors of light. RGB three-primary color LED is also called full-color LED. This LED can form various colors of light by combining the three primary colors of light - red, blue and green.

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Infrared and ultraviolet light

In addition to visible light LEDs, the application of invisible light LEDs such as infrared and ultraviolet light is becoming more and more widespread.

Since infrared light has no effect on the human body, it is widely used in many areas around us, including short-distance data transmission between electronic devices such as remote controls for electrical products and smartphones, security cameras, and sensors.

Ultraviolet light (UV) has high energy and may cause skin burns or skin cancer, which has a greater impact on the human body. However, it is also widely used, such as sterilization and deodorization in the medical and health field, and resin curing in the industrial field.

How to distinguish anode and cathode

LEDs have positive and negative poles, the positive side is called the "anode" and the negative side is called the "cathode". The anode (+) is connected to the positive pole of the power supply, and the cathode (-) is connected to the negative pole of the power supply.

In a Lamp-LED, the longer of the two pins is the anode (+) and the shorter one is the cathode (-).

The back of the SMD LED is usually printed with a mark in the shape of "◀", "T", "convex", etc. to indicate the direction of the current. In the LED, the current flows from the anode to the cathode, so the electrode pointed by the tip of "◀" is the cathode.

For reflective LEDs, the side with the missing corner is usually the cathode. However, since polarity varies by manufacturer, be sure to check the polarity with the dimensional drawings in the data sheet before use.

RGB three-primary color (full color) LED is a product that integrates three light-emitting elements "R (red), G (green), B (blue)" in one package. Its circuit structure includes 6-pin type with each light-emitting color independent, 4-pin type with a common anode or common cathode, etc.

The one that shares a common anode is called the "common anode" type, and the one that shares a common cathode is called the "common cathode" type. "Common" means "shared".