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Name: Arden B.
Status: educator
Age: 50s
Location: N/A 
Country: N/A
Date: 10/9/2004


Question:
What happens when a 220 volt light bulb is operated at 110 volts? I have heard that it has about the same illumination and a significantly longer life span. Is that true? Do you have a reference to verify this?


Replies:
The amount of light given by an incandescent light bulb depends upon the temperature of the filament. This temperature depends upon the resistance of the filament and Ohm's Law (V= I*R) where V is the applied voltage, I is the current in amperes and R is the resistance of the filament in Ohms. Now a given wattage bulb rated for 220 volts has a filament that has a resistance which depends upon the metal type (usually tungsten), its length (usually they are wound like a spring but not always), the diameter of the filament (actually its cross sectional area) and the temperature of the filament. If the voltage is only 110 volts the temperature of the filament will be substantially lower than the same filament carrying a voltage load of 220 volts. Consequently, less light is given off but the life of the filament is longer because it is at a lower temperature. You can see an analogous effect in a flashlight when the batteries start to die. The light gets dimmer because less current is produced by the battery due to its loss in voltage.

Vince Calder


Arden,

You heard wrong! If you have two 100 watt bulbs, one designed for use at 110V and the other at 220V, the 220V bulb will have four times the resistance of the 110 watt bulb. This is because the power used by a device or resistance R when used at a voltage V and current I is given by:

P = IV = V^2/R

So when the 220V bulb is used at 110V, the power used is 25 watts, since the voltage is halved and power goes like the square of the voltage. Since the resistance of the filament increases with temperature, the current is somewhat higher than 1/2 the current at 220V, but you will see a very dim filament.

So you will use less electricity if you replace the bulbs in your house with 220V bulbs, but your house will be very dark.

Best, Dick Plano, Professor of Physics emeritus, Rutgers University


That information is not correct.

The light output and lifetime of lamp filaments is known pretty accurately as a function of voltage. Briefly: the amount of light that a bulb produces goes as the 3.5 power of the voltage ratio. The lifetime goes as the inverse twelfth power of the voltage ratio. This is for a normal light bulb. Also, the current goes as the 0.55 power of the voltage ratio. Voltage ratio is the applied voltage divided by the rated voltage.

So, for example, if a 220V bulb is operated at 110V, the voltage ratio is 0.5. The light output will be 0.5 raised to the 3.5 power, which is 0.088. It will be very dim! It will make less than one-tenth as much light as if it were run on 220V. It will also be orange in color.

The bulb will last a LONG time at this low output. The lifetime will be increased by 0.5 raised to the inverse twelfth power, or 2 raised to the twelfth power, which is 4096 times as long! It will last for thousands of years.

Light bulbs for photographic work are sometimes overdriven to make a lot of light, but they do not last as long.

For example, suppose a 120V bulb is driven at 140V. The voltage ratio is 140/120 = 1.167. The light output is 1.7 times as much. The actual power consumed is 1.27 times as much, so the bulb is more efficient. However, the lifetime of the bulb is cut down by a factor of 6.35.

For fun, I ran a 12V light bulb on 22V. It was very bright. It lasted 2 hours.

Bob Erck


Unfortunately, the 220 volt light bulb does not work at all in a 110 voltage environment. Several years ago, I moved from Europe to the US and tried the experiment, not a success.

I would guess that the 220 bulbs have higher electrical resistance which precludes their operation at a lower input voltage. I do not have a written reference.

Dr. Harold Myron



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