Egg candling methods and apparatus are provided wherein the optical path between a light source and light detector is monitored for obscuring debris and/or malfunctions. A method of candling eggs includes illuminating an egg with light from a light source; receiving light passing through the egg at a light detector; generating an output signal that corresponds to light received at the light detector for the egg; and analyzing the output signal to determine whether the optical path between the light source and light detector has been altered. In response to determining that a respective optical path has been altered, the light source and/or light detector is cleaned and/or inspected for malfunctions. Cleaning the light source and/or light detector may include wiping a surface of the light source and/or light detector and/or spraying a surface of the light source and/or light detector with a fluid.