A measurement system for wide dynamic range operation in optical power measurement applications is disclosed. The system provides amplification over a wide dynamic range without glitch, signal loss or transient effect during range switch. This is achieved by combining first and second multi-gain photodiode amplifiers (10/1,10/2), with their input ports connected in common to receive the input signal from a photodiode, and by switching their gain settings to get continuous readings of a photodiode signal. More specifically, the gain setting of the first amplifier is changed only when the signal from the other amplifier is being output, and vice versa. Such an amplification system ensures a smooth transition within a wide dynamic range while monitoring various signal levels, e.g., monitoring processes with substantial variations of optical power from very high levels to very low levels.