The forward voltage drop (VF) and the forward current (IF) curve, we can know that when the forward voltage exceeds a certain threshold value (about 2V), that is, after the common conduction voltage, it can be considered that IF is proportional to VF. See table is currently the main ultra bright LED electrical characteristics. From the table we can see that the current super bright IF the highest LED up to 1A, while the VF is usually 2~4V.
Due to the optical properties of LED are usually described as a function of the current, and voltage is not a function of flux (phi V) and if the relation curve. Therefore, the driver can better control the brightness of constant current source. In addition, LED forward voltage drop change range is relatively large (up to 1V or more), and by the VF-IF curve in the figure above shows that small changes in VF will cause a larger, IF changes, which caused the larger changes in brightness. So, the voltage source driver cannot guarantee the consistency of LED brightness, and influence the reliability of LED, life and life. Therefore, the super bright LED is usually driven by constant current source.
LED temperature and flux (phi V) curve and by the chart below shows the luminous flux and the temperature is inversely proportional to the, 85 DEG C when the flux is 25 DEG C when the half, and a 40 DEG C time output is 25 DEG C 1.8 times. The change of temperature has a certain effect on the wavelength of LFD, so the good heat dissipation is the guarantee of LED to keep constant brightness.