Published: 10 October, 2007

Infrared beams are just low frequency light beams

Can an infrared beam conduct an electrical current?

One could ask, "Can a light beam conduct an electrical current?" An infrared beam is just a low frequency light beam. Infrared means "below red" just as ultraviolet means "above violet." These frequencies of light are invisible to the human eye. Radio waves and microwaves are lower in frequency while x-rays and gamma rays are much higher in frequency than visible light. All of these waves, rays and beams are part of the electromagnetic spectrum.

Electrical current involves the movement of charge. In a wire, the current is due to drifting electrons. In salt water, it is the flow of sodium and chlorine ions. An electrical circuit has to be closed in order for current to flow. In a flashlight, for example, turning on the switch closes the circuit involving the battery and the lamp.

Current flows easily in metals and salt water because the charge carriers are free to move. In insulators, the electrons can not move easily. Air is a very good insulator. But with high enough applied voltage even air breaks down and conducts, for example, when lightning strikes. I suppose an extremely high power light beam of the right frequency could ionize the air, thereby allowing the air to conduct electrical current.

Although a light beam does not itself carry electrical current, it does transmit energy. One can feel the energy radiated by the sun or a heat lamp. A microwave oven cooks food by transmitting electromagnetic energy onto the food. The remote control for your television probably uses infrared waves to transmit its signals. Light is a very good way to transmit signals when one does not want electrical current to flow.

In our particle accelerator, we use optical isolators to electrically isolate signals. We also use optical fibers to transmit signals to our electron source which floats at 130,000 volts. In these devices, a light emitting diode (LED) converts current into light which illuminates a diode junction to produce current at the receiving end.

Here is one more intriguing property of light. A light beam (or radio wave, or x-ray beam) actually consists of massless, chargeless particles called photons. Even so, it is usually more convenient to describe light in terms of waves, so people usually characterize light in terms of wavelengths and frequencies.