Light Sensing with an LED

Many robotic applications require a sensor to measure light levels. The conventional approach as shown in Figure 1 uses an A/D converter to measure the voltage drop across resistor R1 produced by the photo current through a photo transistor. The fixed value of R1 limits the light range which can be measured; a high resistor value is suitable for measuring low light levels while a low resistance is good in bright conditions. The resolution of the A/D converter also plays a part in determining the range of light levels that can be measured.

www.merl.com/publications/TR2003-035/