Thermal properties of LED
The optical parameters of the LED have a great relationship with the junction temperature of the PN junction. Generally, the temperature rise of the LED is not obvious when the LED is continuously lit for a long time at a small current IF<10mA or 10-20mA. If the ambient temperature is high, the dominant wavelength λp of the LED will shift to a long wavelength, and L0 will also decrease, especially the influence of temperature rise on the reliability and stability of the LED. The relationship between the dominant wavelength of the LED and the temperature can be expressed as
λp(T′)＝λ0(T0)＋ΔTg×0.1nm/℃ (1-1)
It can be seen from formula (1-1) that whenever the junction temperature increases by 10°C, the wavelength shifts to the long wave by 1 nm, and the uniformity and uniformity of the light emission deteriorates. For luminaire light sources used as lighting, miniaturization and dense arrangement are required to increase the light intensity and brightness of the unit area. Special attention should be paid to the use of good heat dissipation luminaire shells or special ventilation equipment to ensure long-term stable operation of LEDs.
Read more: Electrical characteristics of LED
Luminous quality of LED
The luminous quality of LED is mainly manifested in the following three aspects:
(1) Luminous brightness of LED. The LED lamp cup and gold wire will not affect the brightness of the LED, and the main factor that affects the brightness of the LED is the LED chip.
(2) Life of LEDs. The main reasons that affect the life of the LED are: static electricity, solder joints, and heat dissipation. These factors are directly related to the gold wire and the lamp cup.
(3) Consistency of LED. The consistency of LED product quality includes angle consistency (mainly the inconsistency of deflection angle and angle size) and brightness consistency (this is related to the quality of the chip used and the quality of the lamp cup). The consistency of LED is related to the production process equipment and the technical level of the operators.
LED is a solid light source. As a new light source, the research on LEDs by major companies and research institutions is in the ascendant in recent years, which greatly improves the light efficiency. The joint venture between Philips and Agilent has developed and produced white LEDs with a luminous efficiency of 171m/W, which has reached the level of incandescent lamps. Compared with incandescent lamps, LEDs have many advantages in performance, as shown in the table in Figure 1.
Limit parameters of LED
The limit parameters of LED are:
(1) Allowable power consumption Pm. The maximum value of the product of the forward DC voltage and the current flowing through it that is allowed to be applied to both ends of the LED. If this value is exceeded, the LED will heat up or even be damaged.
(2) The maximum forward direct current IFm. The limit value of the forward DC current allowed to pass through the LED, exceeding this value can damage the LED.
(3) The maximum reverse voltage VRm. The maximum reverse voltage allowed by the LED, exceeding this value, the LED may be damaged by breakdown.
(4) Working environment temperature topm. The ambient temperature range where the LED can work normally. Below or above this temperature range, the LED will not work normally and the efficiency will be greatly reduced.