This is what it means for me right now in August in NYC:
get out on to my balcony in direct sun, with no shirt, and just lay out for about 20-25 minutes once/day with no sunscreen or sunblock or oil or anything on my skin (im only wearing shorts so my legs, upper body, and face are completely exposed).
I built up to this, though. I started in the beginning of the summer with the exact same scenario but only for ten minutes each day until i noticed a slight overall tan on my skin. Once i noticed the tan, i started increasing my daily exposure time. I suppose i added about 3-5 minutes per day.
Now im at 20-25 minutes full exposure every day that the weather permits. I have never once burned. I have a tan.
The doctors Eades recommend essentially the same thing in their Protein Power Life Plan book.
(I still take Fermented cod liver oil daily by the way.)
And, no, im not really sure what im going to do this winter:/