I'm pretty sure there is Science on this and it is not guesswork, as the wiki lists the specific conditions and amounts by which cave adaptation increases or decreases. I recall Quietust spelling it out in a thread a while back. Not sure how reading the wiki page could make anyone think inside tiles cure cave adaptation, the wording is clear:
If a dwarf is in a "Dark" tile, cave adaptation increases by 1 every tick to a maximum of 800,000 (403,200 ticks is one year, so the maximum is just short of 2 years).
If a dwarf is in an "Outside" tile, cave adaptation decreases by 10 every tick.
If a dwarf is in an "Outside" tile while the sun is out (i.e. not raining or snowing), the following happens:
If cave adaptation is at 604,800 or higher (1.5 years), the dwarf will experience Nausea, Dizziness, Pain, and Fatigue. The dwarf will also receive the unhappy thought "was nauseated by the sun recently".
If cave adaptation is between 403,200 and 604,800 (between 1 and 1.5 years), the dwarf will become Dizzy and experience reduced amounts of Pain and Fatigue. The dwarf will also receive the unhappy thought "was irritated by the sun recently".
Otherwise, nothing bad happens.
Inside Light tiles do not reduce cave adaptation. According to the wiki, they do not trigger the syndrome, either. In fact, the syndrome shouldn't be triggered during rain or snow, according to the wiki. I've had good luck with outdoor archery targets next to the training grounds, the archers shoot down fliers pretty regularly. There aren't really too many nasty flying types, flying thieves like keas are probably the worst you'll see, and anything truly nasty like a megabeast or flying titan will pause the game when it appears on the map, giving you time to get people indoors if necessary.
I usually put some statues outside in a protected area, to encourage idlers to go outdoors once in a while.