I've got a good mercury lamp without an etch. I'm not sure if it's 100w or 175w. I can see the arc-tube but it's not clear to me which watt it's suppose to be because I only have a few "cheap" clear lamps.

Since there are members here fond of "good quality" clear mercury lamps, could you take out a ruler and measure for me the correct size of the arc-tube? Is there a list or catalog somewhere where the correct volumes are stated for the 100w, 175w and the 250 watt tubes?

 

Interesting

I have some 250w and some 125w but are all frosted so I can't really tell.

 100w is easy as they come in a smaller bulb size than the 175/250w . Mogul base 100w will have either a ED-23 1/2 or BT-25 bulb .  100w arc-tube is rather tiny : 2 1/2" total length roughly 7/16" dia. . 175w tube looks to be roughly 3 3/8" total length  , roughly 1/2" dia.  . 250w tube looks to be 4" total length roughly 5/8" dia. .

 Hope this helps !

The diameter of my arc-tube is roughly 5/8" & the length 2 1/2". So I think I got a 100w. Somehow I thought the arc-tube was too large to be 100w. This lamp is well made and has plenty of life left, so that's why I kept it. Thanks for the valuable info.

 My measurements came from a GE 100w , a Westy 175w & a Tungsram made 250w