What weakens plastic outside is ultraviolet light.
From the sun.
What weakens plastic inside is ultraviolet light.
From fluorescent lights.
There is some discussion on this.
Oct 18, 2012 - A new study finds fluorescent light bulbs, although eco- and budget-friendly, emit high levels of ultraviolet radiation.
I've converted my house to LED but not my garage.
There will be some weakening of plastic inside .......... maybe ........