Diamond lamps are kind of confusing to me, but I've never bought one to see whats actually stamped on the glass. Some of the websites make it sound like its Philips lamps in a generic housing. But, from what I read Diamond develops and manufacture replacement projector lamps, using bulbs identical to those originally supplied with the projector.
Also somewhere I read about a company that Philips acquired that built lamps, and then let them be endorsed by Philips, but the lamps still aren't actually built by Philips. The problem is I cannot remember if it was Diamond. But at least in the UK it appears Diamond is involved with Osram also.
So the best thing to do is the same that has been discussed in other threads, take the lamp/bulb out of the housing and see what info is on it. Is Philips stamp on the Diamond lamp? Does it give the specs? If so then should be easy to find a actual Philips lamp without a housing. I mean they are the one's that actually built the lamp for the RS20 line.
Still, it seems like if Philips is that involved with Diamond they should be OK. Yet Philips sold their TV' business out to Funai in USA & Canada. So Funai is in control of building them with using the Philips name. But in most of the rest of the world, especially Europe its still Philips building them. So that's certainly not the same.
Still, I don't see why its so hard to find a Philips lamp for the RS20 since the original was built by them. Where as the RS1 was not but I was able to find a Phillips for it.
This is kind of a boring link with Philips and Diamond talking to each other.http://www.genuinelamps.org/video/dl/