They can’t be used in closed fixtures.
“They can’t be used in closed fixtures.”
Says who? And why?
I’ve been using a 100W-equivalent one in a closed fixture - no problems yet. I’ve got two in a closed fixture with along with a 60W incandescant - again, no problems. I’ve also got them outdoors, hanging downwards (supposedly a no-no) where they work fine (but take a little while to warm up) in temperatures well below freezing.