IPX-1
An IPX-1 rated device can stand up to rain for a short amount of time – as long as it is in a normal horizontal or vertical position. In order to be awarded this rating, the item must function after being exposed to 1mm of falling water per minute for ten minutes.
IPX-2
A device that receives this rating will withstand falling rain coming in at an angle not greater than fifteen degrees – think a nice driving rain but not a torrential downpour. In order to be awarded this rating, a product must function after being exposed to 3mm of falling water per minute for ten minutes.
IPX-3
This is a device that will survive a torrential downpour. It can continue to function in rainfall up to sixty degrees from vertical. In order to be awarded this rating, a devuce must function after being exposed to .7 liters of water at a pressure of 80-100 kN/m2 per minute for 5 minutes.
IPX-4
This is the splashing water rating. Essentially, your item will survive any splash of water from any direction. In order to be awarded this rating, a product must function after being exposed to 10 liters of water at a pressure of 80-100 kN/m2 for five minutes.
IPX-5
With a rating of IPX-5 or greater, you could dowse your item with a garden hose and it would still work. In order to be awarded this rating, a product must function after being soaked with 12.5 liters of water at 30 KN/m2 at a distance of no more than 3 meters for three minutes.
IPX-6
If the IPX-5 can withstand a garden hose, the IPX-6 rated device can withstand a fire hose. IPX-6 flashlights must function after being exposed to 100 liters of water per minute at a pressure of 100 kN/m2 at a distance of no more than three meters for three minutes
IPX-7
IPX-7 and above deal with items that continue to function after being immersed in water – dropped in the lake. In order to receive a rating of IPX-7, a flashlight must function after being immersed in 1 meter of water for 30 minutes.
IPX-8
An IPX-8 device will continue to work underwater indefinitely.
info from http://www.survivaledgelights.com/ipx-rating/