Candling is the practice of passing a bright light behind an egg so the interior becomes visible through the shell. The name dates from when a candle was used; modern grading lines use high-intensity LED candlers, often automated. It lets graders see hairline cracks, blood or meat spots, air-cell size and any abnormality in the yolk or white without breaking the egg.
In an export operation, candling sits alongside optical weight grading and acoustic crack detection as one layer of several. Eggs that fail are pulled before packing, so what reaches the master carton is sound and uniform. For buyers, candling matters because interior defects are invisible from the outside: a carton can look perfect yet hide cracked or spotted eggs. A supplier that candles every batch is screening out exactly the problems that cause complaints and breakage claims on arrival.