Came across a listing for a Sylvania 50w HPS bulb, what I think makes it rare is that is is diffused, not clear, and has a Mogul base. Is this actually rare or do I just think that. Price for it is $14.99 and no shipping fee. Or should I get a Philips Lifeguard 75w B21 coated MV for $11.99+$4.99 shipping, if that would be rarer. BTW there are over 10 of the lifeguard lamps but only 1 of the Sylvania lamps.

I’d say the Sylvania is simply uncommon, I’ve seen quite a bit throughout the years on the eBay. I’d consider (for example) a HPS Clearbander as rare. Most of the stuff I see are usually Osram era, some GTE. What also increases the value is the generation, since Sylvania revised the design a few times between the early 1980s to 2000, like going between BT, ED, and ET envelopes.

Really it’s personal preference, if really want the Sylvania… go for it.

Not sure if it matters but it is a BT shaped bulb

Here's a image taken from the listing.

Ok, I know that seller. It’s a Osram-era ET shape. Fairly recent.

So is the Philips Lifeguard 75w B21 MV worth the slight extra over this HPS bulb?

Yes.

OK. I am looking towards having my first MV lamp.