I was confused as to why these were discontinued. I can sort of understand why coatings such as /C and /R were discontinued, but why /W? It seemed like an efficient, effective coating that was not expensive to make. Why was it discontinued early?

I believe they were made obsolete when /DX mercury lamps were introduced as the /W more or less only had the same light output as the /DX but with worst colour rendering. The lumen ratings I pulled from the literature seem to support this.

175w /W lumens:
Initial: 8000, Mean: 7000

175w /DX lumens:
Initial: 8500, Mean: 7600

It's been a while since I lit my /W lamp so I can't really comment on the perceived colour rendering compared to a /DX.

I believe they were made obsolete when /DX mercury lamps were introduced as the /W more or less only had the same light output as the /DX but with worst colour rendering. The lumen ratings I pulled from the literature seem to support this.

175w /W lumens:
Initial: 8000, Mean: 7000

175w /DX lumens:
Initial: 8500, Mean: 7600

It's been a while since I lit my /W lamp so I can't really comment on the perceived colour rendering compared to a /DX.

Thank you for the info. I guess it does make sense that /W lamps were discontinued after the introduction of /DX, because the lumen output was similar and /W still had a much worse CRI. According to some Westinghouse lamp catalogs I have looked through, the /W lamp was discontinued in 1975 as well as their /C lamp.

That info comes from the 1975 large Westinghouse lamp catalog.
https://www.scribd.com/document/112839524/Westinghouse-1975-Large-Lamp-Catalog

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It's been a while since I lit my /W lamp so I can't really comment on the perceived colour rendering compared to a /DX.

Do you have extra /W lamps you could sell to me?