I recently learned of this as well. I had no idea until someone mentioned it in conversation.
Some of the info I've read said that they can be up to 3mR/hr, which as I understand it means that the lens would have to be in your pocket, 8 hours a day, 40 hours a week, for 6 months straight before you'd have the recommended annual "dose".
Don't hold that lens close to your jewels if you want kids
“We are buried beneath the weight of information, which is being confused with knowledge; quantity is being confused with abundance and wealth with happiness.
We are monkeys with money and guns.”