Floodlights are known mostly for two things - short life and high cost. And significant energy consumption. I guess that's three things.
My Instructable will halve the amount of power used, and with that, will dramatically increase bulb life. When bulb life goes up, cost goes down. I can't even say accurately how long the bulbs will last - perhaps years in typical use.
Step 1: List of Materials
This instructable requires three main things: a floodlight, a diode like a 1N4004, which will cost you perhaps a nickle apiece at suppliers like Jameco Electronics, and a piece of electrical tape. You will also need the tools and ability to solder a couple of connections.
Step 2: Look for the Notch
The bulb should be either a 75 watt or a 100 watt variety - you can go higher, but if you go lower, you won't get much light, as this method essentially cuts the light in half, too. The bulb also must be the kind with a 'V' notch cut in the side of the base, as shown in the photo. When you look at your bulb, you will see a wire coming through the notch. This is important to the project. There are other bulbs without the notch; you won't be able to use one of those.
Step 3: How to Do It
First, using a tiny screwdriver or knife point, disconnect the wire that comes through the notch from where it is soldered to the screw base of the bulb. This is very easy; it is hardly soldered at all. Leave the other end inside of the base intact. Sand an area at the top part of the screw base, the part farthest from the tip of the base. Do about half an inch about one third of the way around the base from the notch. Get it nice and bright. Heat up your soldering iron and tin the sanded area of the base. Cut the leads off the diode about 5/8” from the diode body. Solder one of them, it doesn't matter which, to the wire running through the notch so that the diode makes a sharp turn and runs parallel to the threads in the base. Press against the diode so it bends to conform to the base curvature.
Step 4: Summing Up
Using a piece of electrical tape, insulate the base from the diode on the soldered side. This is important. If you mess this up, the bulb will short out and blow your circuit breaker. Now, solder the other end of the diode to the place where you tinned the base. Wrap the top of the base and diode with electrical tape. That's the entire project. It cost's next to nothing, not counting the bulb, and it will result in a floodlight that is very long lasting and which burns half the rated power.
Again, it isn't quite as bright as it would have been, but it works very well.