In et, Steve Kraus wrote:

Eh...ditch the fluorescents and MH's and get *low* pressure sodium. Not
the pinky yellow of most contemporary streetlights (high pressure sodium),
LP sodium give that nice almost monochromatic yellow which you don't see
much of anymore but used to be used for parking lots and some streets.
IIRC more lumens per Watt than anything.

Is this sarcasm?

Low pressure sodium does indeed achieve more lumens per watt than
anything else, but I would not use it even to illuminate a parking lot.

The monochromatic orange-yellow light turns everything into an
orange-yellow version of black-and-white!

Reds become dark gray or black, except for a few fluorescent reds.
Oranges become gray. Yellows and whites look identical. Greens become
shades of gray. Blues become shades of gray, sometimes black. Purples
become shades of dark gray. (Technically brighter or darker shades of
orange-yellow, but when you are only seeing orange-yellow different shades
start to look like shades of gray.)

Most colored objects appear darker under low pressure sodium than under
other light. Because of this, I would not consider a lumen of low
pressure sodium light to have as much "illuminating power" as a lumen of
another kind of light.

I thought the lowest possible color rendering index was zero until I
heard that low pressure sodium rates a -44.

- Don Klipstein )