Here is a project I made a few years ago when I almost fell down the steps in the dark. My home is very dark at night and I have added night lights wherever a dark area made it difficult to safely walk through. Night lights also give a warm appearance to the rooms they are in. Automatic night lights help to conserve power and are a wise choice for areas with good light during the day.
Since this project is finished I can not show all of the steps in installing these lights. I try to be frugal in keeping with the spirit of Instructables. So many computer power supplies are thrown out that can still be used. It is a shame that how many of these power supplies are sent to the landfills instead of being put to use.
I would like to stress this project requires modifications the a computer power supply and should only be attempted by those possessing the necessary skills to do so safely. Inside the power supply case there are 120VAC wires that can be lethal if touched with power on. Safety is of upmost importance whenever working with electricity. Even low voltages like 5 or 12 volts can ark and burn if not handled safely. Use common sense with this or any other project dealing with electricity.
Step 1: Basic Construction Concepts
This is what my stairway light look like at night. I had to use tripod on the camera to steady it for the relatively long exposure times. There are two sets of stairs in my house. One stairway has two lights and the other has just one.
Step 2: Parts
An old computer power supply.
A board to mount the power supply on.
Terminal strips of some sort that can be mounted on the board.
Outdoor landscaping lights that can be mounted on a flat surface.
Wire - I used #14 romex wires with the sheathing (outer white insulation) removed.
Optional LED and 1K resistor (brown - black - red) .25 watt or higher.
Metal plate to mount electrical parts. This one is from a Hoffman electrical box.
Miscellaneous screws, tools.
Optional power resistor. See text.
Step 3: Computer Power Supply
Salvage an old computer power supply that still works. The power supply must be mounted to the metal plate or plywood back in some way. Here I invite you to use your imagination. Make sure the power is mounted in such a way as to allow air to freely move to cool the power supply. I think a computer power is far superior to the one offered by the manufacturer. The computer supply is regulated and will hold it's voltage and therefor the bulb's brightness over a wide range of loads.
I use an old computer supply for my outdoor landscape lighting as well. It is in an old plastic box with a locking cover. A couple of holes in the side allow the wires into and out of the container. About once every two years or so it has to be replaced. The 12 volt outputs of the power supply are used for outdoor lighting.
The power can supply two useful voltages to us: 5 VDC and 12 VDC. Sometimes in order to obtain the most pleasing mood I will operate a higher wattage bulb at 5 volts instead of 12 volts. They can also be connected in series like Christmas tree lights to divide the voltage. When using this method it is best to use the same wattage bulbs to keep it simple. To compute the voltage for each bulb, divide the voltage used (12) by the number of bulbs in the string. If you are connecting 2 bulbs in a string (called in series in electronics) each bulb will get 6 volts.
Be sure to use wire that can carry the load. If you are running three or four bulbs it should be no problem. A 12 volt bulb rated at 12 watts will draw 1 amp. You can compute this yourself by using the formula Amps = Watts divided by Volts. Assuming you are using the same wattage bulbs running at the same voltage you just add up the wattages and plug them into the formula.
If you plug in the power supply without modification you will notice nothing happens. A small modification must be made to the power supply to make it come on without it being installed in a computer. On an ATX type power supply connect the green wire to a black wire. All of the black wires are connect to negative.
Step 4: Light Fixtures and Bulbs
Here are three options I found on the net. I used the copper finished unit on the left. A company named Malibu makes a large assortment of landscape lighting. They are worth looking into and can be found at almost every Home Depot, Lowes, K-Mart, Sears or any home improvement center.
The fixture I used takes 7 watt 12 volt incandescent light bulbs. I prefer the soft orange glow of incandescent lights over the harshness of most LEDs. Some of the wedge base light bulbs are available in 4, 7, 11 and 12 Watt versions.
It is getting more difficult to find incandescent lights since they are being phased out in favor of the more efficient LED version. Incandescent means the light is created from a white-hot wire called a filament. Similar to the first one Thomas Edison made.
You may want to disassemble and paint the light before installation. It is all a matter of personal taste.
For the really daring among you may want to try building your light fixtures. The bulb sockets are available separately.