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Explanation of Important Parameters of LED


1.Forward current If:

It is the forward current when the light-emittingdiode normally gives off light. The IF which is less than 0.6•IFm shall be chosen according to the requirement in actual use.

2.Forward voltage VF:

The operating voltages shown in the parameter list are derived from the given forward current. Generally it can be measured at IF=20mA. The forward voltage VF of the light-emittingdiode is from 1.4V to 3V. VF will fall with the rise in temperature.

3.V-1 Characteristics:

Relationship between the voltage and current of light-emittingdiode: when the forward voltage is positively less than a certain value (threshold), the current is very small and it does not give off light. When the voltage exceeds a certain value, the forward current will rapidly increase with the voltage and it will give off light.

4.Luminous intensity IV:

The luminous intensity of the light-emittingdiode is usually referred to the luminous intensity in normal direction (the axis for the cylindrical luminotron). When the radiation intensity in this direction is (1/683) W/sr, it will give off 1 cd of light. Because the luminous intensity of the LED is generally small, the luminous intensity often adopts candela (candela, mcd) as its unit.

5.Luminous angle of LED:

-90°- +90°

6.Spectral half width:
It represents the spectral purity of the LED.

7.Half-value angle θ1/2 and visual angle

The θ1/2 is the included angle between the direction in which the value of the luminous intensity is half of the value of axial strength and the luminous axial direction (normal direction).


It is the angle calculated according to the luminous solid angle and it is also called plane angle.

9.Visual angle:

It is the maximal luminous angle of LED and according to the difference between of the visual angles; its applications also can be different and it is also called light intensity angle.


The included angle between normal direction 0° and maximal luminous intensity of 1/2. Seriously, it the corresponding included angle of maximal value of the luminous intensity and the maximal value of the luminous intensity of 1/2. The maximal luminous angle is not the value of the normal direction 0° which is caused by the encapsulation technology; introduction of the angle of deviation, it is the included angle between the corresponding angle of maximal luminous intensity and the normal direction 0°.

11.Maximal positive direct current IFm:

The maximal positive direct current which is allowed to be added.

If it exceeds the value, the diode can be damaged.

12.Maximal reverse voltage VRm:

The maximal reverse voltage which is allowed to be added

If it exceeds the value, the diode can be broken down and damaged.

13.Operational environment topm:

The ambient temperature range in which the light-emittingdiode can normally operate

When it is below or above the temperature range, the light-emittingdiode will not be able to normally operate and the efficiency will be greatly reduced. [1]

14.Allowable power consumption Pm:

The maximum of the product of positive direct current and the current flowing through it which is allowed to be added to both ends of the LED

If it exceeds the value, The LED will generate heat and be damaged.