Long Life for Floodlights





Introduction: Long Life for Floodlights

About: When I was a boy, I was amazed how my grandfather could make flotsam and jetsam into useful things. I am proud that I have inherited some of his skill.

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.



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    13 Discussions

    Ah bunch of years ago I remember seeing a Button Diode you would screw into the fixture and then screw in the light bulb. These were sold on the east coast where I lived at the time and then they went away. I thought the bulb manufacturers had them removed from the market.

    1 reply

    I remember them, too. I have looked for them and can't find them. This amounts to the same thing, although admittedly, it would be easier to insert the other device into the socket and screw in the bulb.

    Good idea. You could also do this in the socket or main lead itself by putting the diode in the power lead without soldering by using a power block, which is easier and means you can just put in an unmodified bulb, or one without the notch. To get the total light amount back but with longer life, just use two bulbs in parallel of the same lead or use two diodes in two leads, each in opposite directions so each ac direction feeds alternate lamps phase.
    You could also put the diode easily across an inline switch, which would give you half/full light or replace the main single switch with a double switch, wiring the first switch as a normal on/off then concecting through the second switch in series with the diode across the terminals which would act as a half/full power selector.

    1 reply

    Yep, to all the above. But I didn't want to modify anything else in the event that I wanted to put a bright bulb back in its place.

    One thing you didn't mention, which I have done with exterior light fixtures using candelabra lights: I wired the two bulbs in series, which doubles the resistance and halves the voltage available to each bulb. Actually, this works very well from a decorative viewpoint because it makes the bulbs very much resemble a candle. Or at least more like a candle than a light bulb. It isn't very bright, though.

    Thanks, Wobbler, they were all good suggestions.

    Good idea but you should realize that the light drops by more than 1/2 as the efficiency of the bulb drops, I would limit this to hard to change bulbs

    4 replies

    Actually, the light drops by LESS than 1/2, more like 40%. The reason for this is because of the Thermal Lag of the filament. The beauty behind the half-wave rectification (this method of dimming) is that it DOES extend the life of the bulb by more than double that of full power. This is based on my own personal experience with doing this to many incandescent bulbs.

    Three years ago I purchased a dozen 75watt halogen "crystal" mini-flood bulbs for my reptile tanks. I later found out why the lamps were being sold for such a low price, because they lasted about two months!! By putting the diode trick to them however, I have yet to replace one and it has been nearly a full year operating 24/7.

    One thing I wanted to also mention was that the trick is not entirely limited to only the floods that have the notch (or only floods in general). In most cases it's possible to de-solder the button on the bottom of the base by using a solder-sucker or braid. Once the solder is gone you will see a hole with the wire poking through. I have found some of those holes large enough to push the diode through, others I have widened with a small screwdriver. In either case, simply solder one end of the diode to the wire poking through (sorta tough if it's really short) then push the diode through and solder the wire to the button again and cut the excess wire off. If it's too difficult you can pry off the brass button altogether and install the diode in the remaining hole. Then just coil the remaining diode wire in a flat spiral and solder it to resemble the button. Works perfectly every time.

    As a final comment... if the amount of light given off is too low with the bulb you've chosen, do the trick to the next wattage size up, and you will be left with a brightness level closer to what you initially wanted.


    More on the brightness. I do not think thermal lag has anything to do with it, but more thought does throw some doubt on what I wrote ( although I would still claim you get less light per dollar of electricity ) A half wave rectifier into a resistive load will give 1/2 the energy consumption. But a incandescent bulb is not quite a simple resistor, as the temperature goes up the resistance goes down so with a half wave rectifier your get more than 1/2 the power. Now the light given off by the bulb goes as the fourth power of the temperature of the filament, the rest goes as heat. Thus a slight drop in temperature gives a big drop in light. The spectrum shifts towards the red. Perhaps a light meter would be a good idea at this point.

    Thanks for the comment.

    Using 100 watt bulbs, I am satisfied with the amount of light I get in my back yard. They are mounted about 10 feet up, so they aren't hard to change - just annoying. But now they last a long time.

    An unmodified floodlight runs on the electricity coming from a normal household circuit - and one of the defining characteristics of that electricity is that it is "alternating current" - half the time electricity flows in one direction, and then it reverses polarity to the opposite direction. The diode only lets the electricity flow in one direction, so half the time there's no current flow. You won't notice it blinking on and off though, for a couple of reasons... partly because of the way your eye sees it and partly because of the way the bulb makes light.