A new design of interface circuit for CMOS Light sensor for pH monitoring applications is presented here. The proposed design is useful to read color (wavelength) values with the help of a photodiode and output a digital word representing the color value. It operates by continuously comparing analog voltage output from an optical transducer against a pre-stored reference levels in two cascaded stages. The design provides few advantages such as faster speed; higher resolution with smaller number of storage units; and small area for on-chip integration. A simulation result using the CMOS 0.35 AMS technology implementing 32 levels of resolution is presented. © 2012 Praise Worthy Prize S.r.l. - All rights reserved.