Way back in the mists of time GE used to manufacture an item called "Ruby Bulbs".

They were an incandescent light bulb with the glass bulb made from clear natural ruby crystal. They were not specifically designated for photographic use on the packaging but when I started working in family hardware store thirty years ago we had a mixed case of 25 and 40 Watt bulbs gathering dust on the shelf. If I recollect they had already been discontinued prior to my start in the business

Needless to say I immediately placed the Habes Grabbus on them and have been using them in my darkrooms since that time with absolutely no fogging issuses.

My current darkroom has four 4" ceramic lampholders mounted on the ceiling controlled by a separate switch mouned next to my enlarger with them installed.

Hal