People generally accept the led brightness control methods are two, that is, analog dimming and pwm digital dimming. When using analog dimming, the recommended current range is between a maximum value of about 10% of the maximum (10: 1 dimming range). As led by the chromatography and current, so this method is not suitable for some applications. However, the pwm digital dimming mode is switched between a zero current and a maximum led current at a rate that is almost enough to cover the visual flicker (usually higher than 100khz). This duty cycle changes the effective average current, resulting in a dimming range of up to 3000: 1 (limited to the minimum duty cycle). As the led current is either at the maximum, or be turned off, so the method also has to avoid the advantages of led color deviation, and in the use of analog dimming when the color shift is very common.