In article , RPS wrote:

I have to make some decisions about lighting the lobby of a six-flat
building, stairwell, hallways, back porches, as well as a security
light for the yard.

The basic decision is: do we go with old fashioned warm yellowish
lights, or the new cool "bluish "daylight" types?

Any suggestions or experience appreciated.

Hallways should have warm color lights. At typical apartment building
hallway lighting levels, 4100 K and higher easily appears "dreary gray".
Even 3500 K can appear a little "dreary gray". I would use 2700 K - the
usual warm color of compact fluorescents.

If the illumination level is on the bright side, then 3500 K tends to
look good.

As for stairwells - it depends on how much light you have, and whether
they are used routinely or you have an elevator. If they are more dimly
lit, go for daylight color - scotopic vision has a significant enough
effect to make the more-blue light have greater "illuminating power" - but
the stairwells will look dreary.
If the stairwells are to be used routinely, use warm color and be sure
to have enough light.

One thing to watch out for: In my building, the stairwell lights are
fully enclosed. CFLs above 14 watts or so can easily overheat in enclosed
ceiling fixtures.

The lobby should definitely have warm color light.

Back porches - I am leaning to cooler color there, to take advantage of
scotopic vision being likely to have some significant effect.

Yard security lighting: Go for cool daylight color. Scotopic vision
will have a significant role in the sensation of illumination.

Metal halide lamps do well for outdoor illumination at night. Use the
lowest wattage that you can find unless the yard is huge.

Mercury vapor and sodium vapor lamps will not illuminate a yard as well
even for a given amount of photometric output, because they stimulate
scotopic vision less. Despite a more-bluish color, mercury vapor light
does not stimulate scotopic vision as well as metal halide or fluorescent
light.

Your yard fixture should be of a design that throws the light onto the
yard, and not into the sky. Many security lights send a fair amount of
light above the horizon. Look for fixtures of a floodlight style rather
than a "wall pack" style or the style of those traditional 175-watt
mercury security lights. Floodlight style fixtures will put much more
light where you want it, so you won't need to use as much electricity.
A floodlight style fixture with maybe around 50-60 watts of daylight color
compact fluorescent can outperform a traditional 175 watt mercury vapor
fixture for yard lighting.

- Don Klipstein )