Growing Light Bulbs from Sets

Elizabeth Anne Viau
Charter School of Education
California State University, Los Angeles
Los Angeles, California 90032-8143

Published in The Mensa Bulletin, May 1989

To the casual observer, it may appear that technology has appropriated almost every opportunity to practice self-sufficiency. Enterprising persons, however, may still find satisfaction in participating in the modification of their immediate environments. One little known but simple example of these opportunities is growing your own light bulbs from sets.

On the farm, small onion sets are planted every year, and nurtured until they grow into large onions. Similar opportunities exist for growing light bulbs, starting with the small "flashlight bulbs," which mature into the 100 watt variety, or "automotive brake light bulbs," for the larger 250-watt bulbs.

The process is a simple one. We know that glass is actually an extremely viscous liquid, because it has no crystalline structure. Bubbles in liquids maintain themselves with surface tension. We also know that light bulbs are bubbles. Larger light bulbs use more electricity than small ones, and also radiate more heat. Using these facts to guide us, we can construct our growing apparatus.

Light bulbs retain their form because there is a balance between the heat emitted by the filament and the surface area of the light bulb, from which the heat is radiated. If there is too much heat, internal pressure rises and the bulb explodes; if there is not enough, the bulb does not emit a healthy glow. As glass is heated, it becomes more malleable. The trick in getting little bulbs to grow to full size, then, is to over-supply them with just enough power to very gently push the bubble in a slow, controlled expansion.

The beginner should start with flashlight bulbs, because they are thick-walled. While this requires more care at the beginning of the process (a slight miscalculation of current can lead to explosive heat build-up), there is more glass to work with as the bubble expands, resulting in a sturdy, serviceable 100-watt bulb. The grower wraps a metal spring round the base of the bulb and attaches two insulated wires to the spring so that a current can flow through it. The small bulb should be set on an insulating base in such a way that nothing touches the glass. Set the bulb, on its insulator, in a draft free location. The wire leads are connected to a rheostat (allowing the grower to regulate the current going into the bulb), which in turn is connected to the power source.

How much current should you use? A flashlight bulb uses three volts, so you would obviously start at three volts and gradually increase the voltage. By my calculations, for surface area S1 of the flashlight bulb, and recommended voltage V1:

For a 100-watt bulb of surface area S100 and a recommended voltage V100:

The relationship between the surface area of the bulb and the voltage it can support is almost constant. The growth of the bulb is fostered by increasing the voltage slowly and evenly. Local differences in temperature and actual power-line voltages make precise time guide-lines difficult to specify. A suggested approach is to allow a one -hour-per-volt increase: monitor and adjust.

Why do people grow their own light bulbs when fully mature specimens are available in the stores? Some enjoy the convenience of storing the small light bulb sets over the bulky packages that contain the fully-ripened bulbs. Some enjoy the simple self-sufficiency of growing their own, and. for others, growing a light bulb is the modern-day equivalent of growing a hyacinth in a glass of water. Whether the motivation is practical or aesthetic, enterprising and venturesome persons will find enjoyment in this safe, clean, and productive activity.

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© Elizabeth Anne Viau, 1989. This material may be used freely for instructional purposes but not sold for a price beyond the cost of reproduction. Please e-mail me at if you use this material. I'd be interested to know how it works for you!