I only saw as biggest lamp a Siemens Klassiker with 400w HQL. I know this is nothing in comparison with lanterns ,which are used in the USA.

Here in Western Canada the biggest lamp I've seen is 400W,nothing higher here except for parking lots,most are 100W or 150W HPS,and 250W to 400W HPS on the highway.

Highest mecury I've seen 400W (before changeover to HPS)

Highest HPS 400W in: Sylvania Powerlite B2255,McGraw Edison Unidor 400,Hubbel RLG

Joseph just reminded me...We do have some high mast fixtures here as well along the #1 or 401 Freeway at some of the interchanges which have several 1000W HPS fixtures on each mast,three of the masts that were installed have never been used , which are closer to where I live,that must be why I forgot about them. 

The highest I've seem here in Eastern Canada-Ontario is 1000W HPS which is used in some highway highmast fixtures. For regular streetlighting the highest I've seen is 400W HPS,

The highest mercury would possibly be 400W(I don't think 700W or 1000W lamps were used here). I've seen 400W MH fixtures in Quebec but the highest in Ontario I've seen is 250W 

I have seen 1500w Metal Halide, in a parking lot light. I actually have a ballast from one and it weighs 30 pounds!

1000 watt mercury vapor (and I own one too.)

SOX 180w LPS lamp. and 250w HPL-N MV lamp.

I THINK the local fleet farm has 1KW HPS. There are only four of them in the entire lot, so they must be pretty beefy. Wait... I guess that doesn't qualify as a street lamp, does it? In that case, I've only seen 400W MH and 400W hps.

The main roads in my area used to have 400 and even 700w mercury lamps - now 400w HPS. Even the smaller arterials use 250w HPS and I have even encountered residential neighborhoods using 200w HPS! Downtown Seattle uses 400w HPS cobraheads plus 150w HPS (x3) for sidewalk lighting and 400w HPS floods to light storefronts & bus shelters. Overkill - I think - although the ultimate winners are the local shipyards with huge clusters of 1000w HPS floods, with as many as 16 per pole.

Highways commonly have 400w HPS lamps but some high-mast lighting have used 1000w lights with as many as six fixtures on one pole!

Residential neighborhoods are typically 100w HPS. Even residential yard lights can be easily found at hardware stores with 150w HPS lamps. Only in America - where we're aiming to be bigger & brighter than the rest of the world.