http://en.wikipedia.org/wiki/Tanning_bed http://en.wikipedia.org/wiki/Sun
I have a 4-year-old macbook pro with a matte display that I occasionally sit with on my back portch. It works well enough in shade but not in direct sunlight.
My main source of sunlight, though, is it taking a 30 to 40 minute break to take a walk once or twice a week.
To the OP: if you want to combine work and being outside and have everything that's necessary - basically a laptop which won't immediately overheat and whose battery is still doing alright (+ a WIFI stick if you need internet[1]) - go for it! If you don't have a matte display, look into privacy filters/screens (the one I have is shiny on one side and matte on the other), though those obviously work best on screens with a good backlight, even more so in sunglight.
If you do end up working outside, don't forget to use sunscreen and to stay hydrated!
[1]Alternatively, search for cafés with free WIFI that have outdoor seating or turn your phone into a WIFI hotspot (beware of mobile data costs though).
It's a solved problem.
Repeat 2-3 times a week and you'll get some color + light exercise.