# Diode in series with light bulb

Discussion in 'Electronic Basics' started by steve, Dec 20, 2005.

1. ### steveGuest

I was reading a web site that has information about light bulbs. Here
is a quote relating to a question I wanted to ask.

-- Quote ---
"Reducing the voltage applied to a light bulb will reduce the filament
temperature, resulting in a dramatic increase in life expectancy.
One device sold to do this is an ordinary silicon diode built into a
cap that is made to stick to the base of a light bulb. A diode lets
current through in only one direction, causing the bulb to get power
only 50 percent of the time if it is operated on AC. This effectively
reduces the applied voltage by about 30 percent. (Reducing the voltage
to its original value times the square root of .5 results in the same
power consumption as applying full voltage half the time.) The life
expectancy is increased very dramatically. However, the power
consumption is reduced by about 40 percent (not 50 since the cooler
filament has less resistance) and light output is reduced by reduced by
visible light)."

---
My question is really just a just wondering kind of question. I have no
interest in doing this.

I have seen the type of "Savings " devices written about above. Would
the same thing be achieved if I simply took a diode of the proper
rating and put it in line in one of the wires running to an
incandescent light bulb?

Thanks

2. ### Ralph MoweryGuest

Yes, you would get the same effect. Unless the bulb is in a hard to reach
place you would be beter off just reducing the wattage of the bulb. The
calculations I have seen (not verified) say you will save more on
electricity than the extra bulb replacements will cost.

3. ### Don BruderGuest

Yes, since that's precisely what's going on.

However, you need to be particularly aware of the fact that, besides
using roughly half the electricity, your bulb will also put out MUCH
less light - IME, a 60 watt bulb with one of those things attached to it
is reduced to about the output of a refrigerator bulb. Another
consideration is the flicker-factor - The claim is that there will be no
flicker, but I'll dispute that with my dying breath - Maybe for "Joe
Average" there's no flicker, but to *MY* perception, it's there, highly
apparent, and *EXTREMELY* distracting. Does that mean I've got "super
vision"? <shrug> Idunno. All I can say for certain is that there is
indeed some serious flicker, it'll drive me to distraction in about 20
minutes, and if I don't leave the area, it will induce an all-out "I
think I better go lock myself in a dark, soundproof, sealed, odorless,
padded room with a drain to puke down for about the next three days so I
don't end up killing myself or an innocent bystander" migraine within

And *DO NOT* try to use such a gizmo with *ANY* variation of the
"replace your incandescent bulbs with our cooler, cheaper-to-run
flourescent version" units on th market today - The failure of the
ballast transformer when it gets fed DC instead of AC can be quite...
Well, let's say "interesting" - If you consider having a lamp start
spewing sparks and dribbling molten metal and plastic to be interesting,
that is...

(DAMHIKT...)

4. ### steveGuest

Yes I wondered the same thing about the flicker factor. I'm not sure
how often the /\/\/\ waves alternate ( I know you all know this by
heart, I'm a novice) but by cutting it in half or there abouts, has to
have some effect. also I wonder out loud, if the half wave can set up
some sort of resonance depending on the voltage of the bulb and give an
annoying noise ??? I don't know only guessing.

Thanks again

5. ### Don BruderGuest

Usually 60 Hz (US), and 50 Hz (Europe) - If put to a speaker (through a
suitable resistor, of course! Otherwise it's Insta-Fry(TM) time for Mr.
Speaker) the socket in the wall would output a low, *LOUD* (unless the
resistor was good and beefy) hum.
I imagine it could be possible for a bulb's filament to start vibrating,
possibly audibly, but I'd expect it to be an unusual situation, probably
confined to specific bulbs from a specific batch of a specific brand.
(AKA "I think the odds are against it, but I won't call it impossible.")

6. ### Warren WeberGuest

Steve.. I have done this (added diode in series) . Had a porch light that
always had a short life. I installed diode and a higher wattage bulb to get
the same brightness. No more problems. W W

7. ### Guest

Ive been told that you can also take 220 volt bulbs..in a suitable
base... and feed them 110 volts to increase bulb longevity in a
situation where bulb replacement is difficult.

8. ### The Cheese MachineGuest

Much less VISIBLE light... a lot of it is downshifted to infra-red with
the lower filament temperature. Might be OK if it's to be used with a
security camera...?

Easier just to pay the extra \$ and buy a long-life bulb (with sturdier
filament) in the 1st instance.

TCM

9. ### steveGuest

Hey thanks nothing like experience to answer the question definitively.

Regards

10. ### redbellyGuest

Warren, something you might consider is: the extra money you spend on
electricity will more than offset your savings on bulb replacements.
(Of course, that doesn't address the reduced hassle of making the
replacement less often, so it may be worthwhile for you after all.)

Regards,

Mark

11. ### TerryGuest

=>"Reducing the voltage applied to a light bulb... snip...

Try this next Christmas.

For those of us who like to put a little electric candle in every
window of the house, try inserting a diode (1N4005 reccomended) in
series with the "night-light" lamp. The fool things will last forever
and they will look a lot more like real candles than blinding white
points of light.

In the cheap plastic affairs, the socket is usually just pressed into
the upright stalk. Push it out with a long screwdriver, cut and solder
in the diode to one wire (either one, any polarity), and press the
socket back in place. Maybe a dab of glue to keep it from falling out
later would be in order.

Oh, yeah! Unplug the light before working on it.

But you knew that, didn't you!

Cheers--

Terry--WB4FXD
Edenton, NC