You're already obsessive about turning out lights.

You've replaced many of your incandescent bulbs with compact fluorescents.

Your electric bill has begun an impressive descent.

But there may be a lighting energy-suck you're overlooking: night-lights.

They perform valuable functions, of course.

For many kids, they're all but lifesavers, keeping the monsters under the bed.

Most adults see simpler benefits: They keep you from stubbing your toe on the way to the bathroom or waking yourself up with a blinding 60-watter.

Yet at what cost, environmentally?

The incandescent night-lights sold in my local big-box store use seven-watt bulbs. Burning just one for 10 hours a night over the course of a year consumes 25 kilowatt hours.

Think it's inconsequential? What if you could do the same thing for just 1 kWh? That's what the technology of LEDs - light-emitting diodes - brings.

LEDs are even more efficient than compact fluorescents. And they don't contain toxic mercury.

The next holy grail of lighting is to come up with the familiar pear-shaped, screw-in household bulb in LED form. The technology is close, but still not quite there. The lights are too dim and in need of a whiter shade of pale.

But for a night-light, LED technology is perfect.

They come in various styles, most with sensors that automatically turn them off when the room is bright.

They consume from 0.15 to 0.40 watts - roughly one-twentieth that of an incandescent night-light.

If they don't break, one manufacturer claims, they last 100,000 hours, or more than 25 years at 10 hours a night.

They're slightly pricier than incandescents, but the lifetime cost, including the energy, will be less than half.

Still think this is all inconsequential?

What if each if the nation's 116 million households had two night-lights?

If each bulb was seven watts, they would consume 5.9 billion kWh of energy a year. If each bulb was a 0.3-watt LED, the energy drain would be just 254 million kWh.

If you figure 15 cents a kWh - a little more than Peco's rate, but less than PSE&G's - that represents a savings of $851 million a year, or $7.33 per household.

Beginning to see the light?

Which brings me to the DoubleTree Hotel in Sacramento, Calif.

Research has shown that hotel guests often leave bathroom lights on at night so they can navigate unfamiliar surroundings if they get up.

In my experience, you turn on the light, then just crack the door to keep the bedroom from being too bright. What sense does that make?

Lately, I've begun bringing my own night-light. According to one survey, about 16 percent of travelers do likewise.

But the DoubleTree took matters into its own hands and installed automatic motion sensors in 448 guest bathrooms. When the room remained vacant for a certain period, the lights went off. An LED night-light went on.

The hotel saved $8,000 in energy costs the first year, on a trajectory to recover the overall equipment cost in 2.5 years. Plus, it saved in maintenance costs by not having to replace bulbs as often.

Quite a big bump, from such a little light.

Contact staff writer Sandy Bauers at 215-854-5147 or sbauers@phillynews.com. To post a comment, visit her blog at http://go.philly.com/greenspace.