Valve numbers

[Yorkie]

I did try this when I learned of it a a year or so ago. I tried several different LED torches in a dark room on several old valves, but unfortunately, it didn't work for me. I guess there has to be some residual markings to illuminate even though the may not ordinarily be visible, and it may well depend on the method of marking. In my case they were all valves with B9 bases, rather than pre-war valves such as the HL2 in the youtube video, but nothing ventured - nothing gained! The results in the video are certainly impressive.

Anyone tried it with success?