Replacing mechanical timers, Ice*Meister™ Model 9734-REFR installs directly on refrigerator evaporator coils at factory or as retrofit in field. Invisible light is used to monitor silhouette of evaporator coils. Disruption by frost initiates defrost cycle, and defrosting stops when silhouette returns to normal. Without any moving parts, controller suppresses at least 50% of wasted defrost cycles and helps keep food colder. Applications include supermarkets and food service establishments.