Positive voltage drop (VF) and forward current (if) relationship curve, known from the curve, when the positive voltages exceed a certain threshold (about 2V), that is, usually referred to as the conduction voltage, can be approximated, if and VF is proportional. See table is the current main super highlight led electrical characteristics.
From the table, the current super highlight LED is up to 1A, and VF is usually 2~4v. Because the light characteristic of the LED is usually described as the function of the electric current, rather than the function of the voltage, the relation curve of the luminous flux (φv) and the If, therefore, using constant current source driver can control the brightness better.
In addition, the LED positive pressure drop range is larger (up to 1V above), and by the vf-if curve in the above figure, VF small changes will cause larger, if changes, resulting in greater brightness changes. LED temperature and luminous flux (φv) relationship curve, from the following figure that the luminous flux and temperature is inversely proportional, 85 ℃ when the luminous flux is 25 ℃ when half, and a 40 ℃ time output is 25 ℃ 1.8 times times.
Temperature changes in the wavelength of the LED also has a certain effect, so good cooling is the led to maintain a constant brightness guarantee. Therefore, the use of constant voltage source can not guarantee the consistency of LED brightness, and affect the reliability of LED, life and light decay. Therefore, the super highlight LED is usually driven by constant current source.