I will look for the Ikea lamp because I have a 28/2.5 MC Rokkor-X which is being serviced. Like my older MC Rokkor, it has darkened. I think the problem element is in a rear group. When the MC Rokkor-X comes back I will want to work on it. My earlier experience is with a 35/2 Canon FD SSC (1st version). That lens was kept under a CFL bulb with aluminum foil under it. It pretty much cleared the lens but took about five months. I later got another 35/2 FD SSC (2nd version) which is also a very good lens but which has no color problem. If I read the diagrams on the Canon Camera Museum website correctly the optical formula looks like that of the later 35/2 New FD, also a very good lens.
I have a yellowed SMC Takumar in M42 for my Spotmatic. I love the lens for b/w, but I want to shoot color with it and I find the yellowing drops probably a full half-stop from getting through the viewfinder (which at my age is increasingly a problem).
The IKEA lamp arrived yesterday and I picked up the 28/2.5 MC Rokkor-X this morning. Later today I will set everything up and see what happens. The lamp looks like it will be handy for other things too.
After 48 hours under the lamp the 28/2.5 MC Rokkor-X is tremendously improved. There is a very faint cast left. Nothing like the dark yellow/green cast it started with. I compared it to a 28/2.8 MD and a 28/2.8 MD Celtic (last version). I've decided to put the lens back under the lamp for another two days and look at it again then. Now I can find the 28/2.5 MC Rokkor.