For this example I will be using American mercury vapor (H-number), but this applies to American metal halide (M-number) and American high pressure sodium (S-number) as well.

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The earliest mercury vapor lamps (medium pressure and early high pressure), were H1, H2, H3, H4, and H5. This makes sense, I assume they were numbered in the order that they were made, the first one being the 400W H1 medium pressure mercury lamp. But then, from H5 (obsolete 250W high pressure) we go right to H33 (400w high pressure). What happened to H5-H33? Were they all lamp designs that just didn't catch on? That is an awful lot of failed designs if that is the case.

This also goes for S51 (400W HPS), was there anything before that? I have never heard of an S1. How about M47 (1000W MH)? Anything before that?

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Thanks!

High pressure mercury lamps were actually given lower numbers initially. If I recall, the 175W used to be H22, the 1000W H15, 700W was H17 I believe?

And I *THINK* the numbers never overlap, even across different HID types. This gave a rather strange numbering scheme with probe start MHs being assigned numbers in the 40s and pulse start MHs having numbers above 100.