Turning down or off the display isn't just a matter of saving energy for Mother Earth. It is also necessary to produce a condition known to interior designers as "darkness." And the iMac, for some reason, lacks that most simple of hardware amenities: An on-off switch that controls just the display.

The iMac display also lacks a brightness control, which puts it at a disadvantage to televisions manufactured during the Eisenhower administration.

Free software called Brightness Control from Plasm, fills the gap. You run it, and it presents you with a simple slider control that runs from 0.0 to 1.0. Set the slider to 0.0 and your iMac screen turns black. It still emits a sort of techno-Goth glow, but it's a vast improvement on the vast expanse of shining light that the iMac usually generates.

The Brightness Control user interface also includes a reminder that you press the Esc key on your keyboard to de-activate Brightness Control and restore the iMac display to its radiant wonderfulness.

Brightness Control will help keep the peace in the Wagner household. My home office is adjacent to the bedroom, and the iMac screen shines out the office windows and bounces around on the deck and into the bedroom window, keeping my wife awake.

The iMac has built-in, user-configurable power-saving settings that put the display or the whole machine to sleep after it's been idle. But that hasn't been working lately. I'm not sure why, but I run backup overnight and I suspect the backup software was tricking the idle setting into thinking the iMac was still active.

I'm not surprised that Apple forgot to include an on-off display switch in the iMac. Apple is subject to baffling lapses in common sense. They'll make 10 genius design decisions, and then go blank on something simple. Like, say, for instance, how about coming out with a multi-button mouse, guys? And why doesn't the iPhone let you synch its memo pad to the PC desktop, so you can write yourself a note on the iPhone and have it show up on your desktop?

Update 5:21 pm: I'm not the only one to complain about this. The blog Reality Distortion posted similarly in May. The found a utlity, Sleep Display, that puts the display to sleep instantly. I tried that utility, but found that the display wakes right up again.

Good blog, Reality Distortion I'm adding it to my feeds.