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Thursday, September 10, 2015

Low cost to operate night lights

Here in rural Maine there are no streetlights or reflected city light at night so it gets DARK at night.  This means that when the lights are out inside the house it can be difficult to navigate to the bathroom or kitchen.  So for this reason I have liberally sprinkled nightlights throughout the house to make it easy to get around without having to turn on  lights.  
7 W night light
The classic old-style standard 7 W light bulb style nightlight has been obsolete for several years and I personally have never used them but I did the math and calculated that if you are paying $.10 per kilowatt hour (which is about average) for electricity, each one of those old light lights would cost over six dollars a year to operate which is more than many of them cost to purchase new off-the-shelf!  if you happen to have one of these dinosaurs in your home, I encourage you to discard it immediately and upgrade to the newer technologies.

In the past I have purchased three packs of electroluminescent nightlights for around $10-$12 and they tend to last several years before they eventually grow dim and become relatively useless.  I tested one of these lights and found that it draws .033 W for an estimated cost of about 2.5 cents/year.  A few days ago I was in the hardware store and saw a two pack of blue LED nightlights selling for under nine dollars and thought I would try them out.  LEDs draw a little more power at .125 W for an operating cost of around $.10/year.  LEDs are typically rated to last 30,000 to 50,000 hours so I expect these to last 3 to 5 years.

Here are some comparison images of LED (top) and electroluminescent (bottom)  with ambient lighting and lights out:
LED vs electroluminescent night light in ambient light

LED vs electroluminescent night light in the dark
The LED is significantly brighter and cast a visible pool of light in a dark hallway, while electroluminescent ones are just enough to see by, similar to moonlight coming through a window.

There are other types of night lights that contain light sensors and motion sensors so they turn off when they are not needed.  I suspect that those that use a motion sensor consume a fair amount of power even when they are off just to maintain the motion sensor.  (they do, see this blog post).  I leave mine on all the time since their cost to operate is so trivial.