Optoelectronic modules operable to measure proximity independent of object surface reflectivity and, in some implementations, operable to measure characteristics (such as surface reflectivity or absorptivity) of stationary or moving objects are disclosed. The optoelectronic modules are operable to determine, for example, pulse rate, peripheral blood circulation, and/or blood oxygen levels of moving objects, such as the appendage of a user, in some instances. The optoelectronic modules can be used to measure peripheral blood circulation, for example, when a user of the optoelectronic module is engaged in physical activity, such as walking, running or cycling.