LED Technology

1. Diode light emitting colors

Most LEDs can be purchased in one of the following popular colors: blue, red, orange, green (may be standard green, pure green and yellow green).

In certain LEDs there are chips with several (2-3) colors. Another way a LED can be classified is by the plastic body (or the package) – whether it has a scattering agent or not, if it has color or no color. In that case we can speak about colored transparent, colorless transparent, colored scattering and colorless scattering.

2. Diode surface traits

According to the plastic body traits (diode surface traits) LED products can be classified into square, round, rectangular, surface, side, surface mount subminiature LEDs and so on and so forth.

Each of these groups can be also divided into subgroups – for instance, round LED can be divided into several types depending on the diameter: φ2mm、φ4.4mm、φ5mm、φ8mm、φ10mm and φ20mm and so on. Round LED that has diameter of φ3mm is generally noted as T-1 in abroad, while a φ5mm is noted as T-1(3/4), and φ4.4mm is usually noted as T-1(1/4).

The angle distribution condition of the luminous intensity of a round LED may be assessed by the value of its viewing angle. It´s possible to distinguish three types of LEDs according to this parameter:

(1) High directivity LED: High directivity LEDs usually have either sharp head epoxy packaging or metal reflection cavity packaging, and as a rule there is no light scattering agent. The range of the viewing angle for high directivity LEDs is from 5° and 20° or smaller. Such products can be effectively used as a source of local illumination or for building up of an automated detection system along with a light detecting machine.

(2) Standard type LED: This type of LED has the viewing angle range between 20° and 45° and is commonly used as an indicator lamp.

(3) Scattering type LED: This type of LED product has a viewing angle that may range from 45° to 90°. If compared with other types it has more light scattering agent and is used as an indicator lamp with a bigger viewing angle.

3. LED structure

According to this parameter LED can be classified into metal base, full epoxy resin packaging, glass packaging, and ceramic base epoxy resin packaging.

4. Luminous intensity and operating current.

If we classify LEDs according to their luminous intensity the following types are to be distinguished: standard brightness LED (luminous intensity < 10mcd), high brightness LED (luminous intensity from 10mcd to 100mcd), and ultrahigh brightness LED (luminous intensity > 100mcd).

Another way of classifying LEDs is by the operating current: operating current of a standard type LED is from 10 mA to tens mA; operating current of a low current LED is below 2mA, even though it has exactly the same brightness as any standard LED.