Indirect bright light harmful to teak?  

UV polish?
Furniture polish that provides UV protection may help.
Guardsman (sp) is one. Not sure how 'proven' it is. Give it a
try and get back to us in ten years? Kidding.
Oh, and tape down a nice big round vase and don't move it!
even an inch.
That is really the only thing that causes irreversible harm. Objects
on the top surface that never move, but it does take time.
Curious if various woods settle over time. Fade less dramatically
over the years. My kitchen cabinets are teak. Raked with direct
sunlight by a skylight over 50yrs.They should have completely
vanished by now. The cabinet row that does not get direct at all
are not noticeably darker.
Cork is a different story. My entry floors are blond where the direct
sun hits. Very dark brown in the entry closet.
Personally i wouldn't worry so much but everyone is different in that
respect. If you walk in every day and have a hint of worry instead of
just enjoying it, i would cut a fitted piece of leather and use it.
(that is a beauty Daniel!)

Conversely...
I think some timbers..(beech, elm?) darken with prolonged exposure to bright sunlight?

Cherry is a classic example.
The heartwood darkens nicely for the first while. Then, upon continued exposure, goes the other way and eventually ends up a much lighter, and different, hue than when freshly-milled.