Today, designers have more technology choices for ambient light sensors including photoelectric cells, photodiodes, phototransistors, and photo ICs. Each technology has advantages and disadvantages. One of the key criteria for selecting an ALS is its ability to detect wavelengths visible to the human eye in the 380 to 780 nm range. Figure 1 shows a summary of the advantages and disadvantages of available technologies. While cadmium sulfide (CdS) photoelectric cells have advantages of response similar to the human eye, they contain cadmium, a prohibited RoHS (Restriction of Hazardous Substances) material which makes them unusable in the consumer market. As of July 2006, any product containing RoHS-restricted materials cannot be sold into certain markets in order to reduce the environmental impact of electronic equipment waste. Photo diodes have a relatively low dispersion between individual units but a low output that requires an external amplification circuit. Photo transistors have easily obtainable output current but poor temperature characteristics and a large dispersion between individual units requiring additional calibration steps in end products. Photo ICs, also referred to ALS ICs, are the newest technology, developed to address the shortcomings of other ALS approaches. In addition to increased functions possible with integration including amplification, logic control, and shutdown capability, the photodiode sensing has a relatively low dispersion. Both analog and digital photo ICs are available, each having advantages depending on the application. The photo IC has integrated functionality which eliminates the need for additional circuitry that takes up more board space and adds cost. As a result, many designers are making the transition to photo ICs from discrete devices