Light modes were arguably worse on CRTs, especially if the refresh was 60Hz or less. I couldn't take Word for Windows at all seriously until Windows NT and 85Hz CRTs appeared.

I currently use both light and dark themes on Emacs, with a shortcut to toggle between them. Solarised is a great theme for this, as the text colours are the same for both modes. I originally started using a light theme during the day, as so many other apps already do and I disliked the sudden change in brightness when for example switching between Emacs and a web browser.