Energy Transformation in a Light Bulb

Electricity transforms into heat energy when it flows through a light bulb, and some of the heat energy also turns into visible light. This transformation is an example of the law of conservation of energy, which states that energy cannot be created or destroyed but can only change forms. Sometimes these changes are caused by events in the natural world, other times they are the result of human creations like electricity generators, light bulbs, or automobile engines. The forms that energy takes on are called its physical properties.

Electrical energy flows from the power outlet to a light bulb when the switch is turned on. Some of that energy is converted into light energy, and the rest is converted into thermal energy or heat. Some of the heat energy is wasted as infrared radiation, which feels warm to the touch; this is the “wasted” part of the conversion process. Over time engineers have improved how well the light bulb converts electrical energy into useful light and heat.

The light bulb’s filament converts electrical energy into visible light and thermal energy by resisting the flow of electrons. The resistance causes the electrons to gain or lose energy, which is visible as the filament’s varying brightness. The visible light is produced when the electrons emit photons, or radiant energy.

Incandescent light bulbs convert electrical energy into thermal and visible light, but they produce a lot of infrared radiation which feels hot to the touch. Newer bulbs such as CFLs and LEDs use the same principle, but they turn much less of the electrical energy into heat and waste almost no infrared radiation.

When the switch on a lamp is turned off the filament cools and stops absorbing energy. This is another form of energy transformation; the atoms in the filament loose their electrons and drop to lower energy levels, emitting photons as they do so.

In a fluorescent or LED bulb, the electrical current passes through a mercury vapor plasma. This is a gas in which the electrons are excited to higher energy levels, or ionized. When the current is turned off, the electrons return to their low energy levels and emit photons. The result is that the phosphors in the bulb glow, producing visible light and fluorescence. This type of energy transformation is also used in HID (high intensity discharge) bulbs, which are the most efficient of all lamps. They use about 1/3 of the energy of an incandescent light bulb but generate less infrared radiation. They can be expensive to purchase and replace, but they use much less energy than incandescent or CFL bulbs.