IP stands for Ingress Protection and is a global ratings system. It is used to describe how well a product is protected against intrusion of substances like water and dust. The first number following IP refers to the ingress of solid foreign objects. The second number refers to the ingress of liquids. Common IP ratings found in horticulture light are IP65 and IP66.

IP65 – Protected from total dust ingress and low pressure water jets from any direction. 

IP66 – Protected from total dust ingress and high pressure water jets from any direction.