So I was bored and decided to do a Google search to see if a 5000K Mercury Vapor lamp existed and guess what, it does!

5000K Mercury Vapor Lamp

The highest color temperature I have ever seen in a Mercury lamp is 4000K, I can only imagine how awesome a 5000K one looks. Unfortunately, it looks like it is only available in China as that's where the manufacturer is based. It's really too bad they aren't available here in the United States. There was no info given on the CRI but I imagine with the higher color temperature it might be better.

The low-wattage clear mercury vapor bulbs get close to 7000K. I'm pretty sure some of the older fluorescent coatings had a higher color temp than 4200K too.

~5000K is normal CCT for clear MV.
~4200K normally have /DX coated

Medved: I think 5000K would be just the huge 1kW clear mercury vapor lamps, smaller lamps under 200W are more likely 7000K. See here: http://www.prolighting.com/h39kb175.html
Also my 125W clear MV bulb is cooler than a daylight fluorescent.

You are partially right, the CCT of the clear MV i use (EYE HR50W/R and GE HR100A38) is 5700K (dunno how it come i rounded it down... )

Medved, isn't it weird that a 175 watt lamp is nearly 7000K and your 100 watt is just 5700K? I think my 125 watt ones are close to 7000k too.

It depend on the operating mercury pressure (to be more exact on arc length unity load): Higher load mean lower CCT, better CRI and higher efficacy, but need higher pressure and operating temperature, so put more stress to arctube material and electrodes, what might yield (on lower wattage lamps) to or increase the lamp mortality or require more advanced (requiring more accurate manufacture, so more expensive) arctube design (minimize difference between hot and cold spot temperatures).

The 175waters are made as very cheap lamps for US market (they have the same output as european 125watters, about 7500lm for /DX), they are usually of lower pressure design.

The closest you'll find to a 5000K coated mercury lamp in the US are the Feit Electric brand lamps . They appear to have no phosphor, just a diffusing coating. Also, if you can track down one of the early Chinese made clear-top Westinghouse 175w mercs , they have a poor phosphor that gives the lamp a much higher colour temperature, similar to the previous made "High Output White" (/W suffix)lamps.

I have a NOS /W lamp (made by Sylvania) and indeed, the CCT is close to 5000K, maybe a bit higher, though a little more green than white.