Characteristics and electrical parameters of LED

Characteristics and electrical parameters of LEDs
1. The significance of limit parameters

(1) Allowable power consumption Pm: The maximum value of the product of the forward DC voltage across the LED and the current flowing through it. If this value is exceeded, the LED will heat up and be damaged.

(2) Maximum forward DC current IFm: The maximum forward DC current allowed. Exceeding this value may damage the diode.

(3) Maximum reverse voltage VRm: The maximum reverse voltage allowed. If this value is exceeded, the light-emitting diode may be damaged by breakdown. (4) Working environment topm: The ambient temperature range in which the light-emitting diode can work normally. If the temperature is lower or higher than this range, the light-emitting diode will not work normally and the efficiency will be greatly reduced.

2. The significance of electrical parameters

(1) Spectral distribution and peak wavelength: The light emitted by a certain LED is not a single wavelength.

(2) Luminous intensity IV: The luminous intensity of a light-emitting diode usually refers to the luminous intensity in the normal direction (for a cylindrical light-emitting tube, it refers to the axial direction). If the radiation intensity in this direction is (1/683) W/sr, then the light is 1 candela (symbol: cd). Since the luminous intensity of a general LED is small, the luminous intensity is usually measured in candela (mcd).

(3) Spectral half width Δλ: It indicates the spectral purity of the light-emitting tube. It refers to the interval between the two wavelengths corresponding to 1/2 of the peak light intensity in Figure 3.

(4) Half-value angle θ1/2 and viewing angle: θ1/2 refers to the angle between the direction where the luminous intensity value is half of the axial intensity value and the luminous axis (normal).

Twice the half-value angle is the viewing angle (or half-power angle).

The coordinate of the perpendicular bisector (normal) AO is the relative luminous intensity (i.e. the ratio of the luminous intensity to the maximum luminous intensity). Obviously, in the normal direction, the greater the angle away from the normal direction, the smaller the relative luminous intensity.

(5) Forward operating current If: It refers to the forward current value when the light-emitting diode emits light normally. In actual use, IF should be selected to be less than 0.6·IFm according to needs.

(6) Forward operating voltage VF: The operating voltage given in the parameter table is obtained under a given forward current. It is generally measured when IF=20mA. The forward operating voltage VF of the light-emitting diode is between 1.4 and 3V. When the external temperature rises, VF will decrease.

(7) VI characteristics: the relationship between voltage and current of a light-emitting diode.

When the forward voltage is less than a certain value (called threshold), the current is very small and no light is emitted. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage and light is emitted. The forward voltage, reverse current and reverse voltage of the light-emitting tube can be obtained from the VI curve. The forward reverse leakage current IR<10μA is less than 10μA.