The term “light box” can mean a few different things, but from a lighting perspective it typically refers to a backlit display panel. Light boxes are most commonly used for advertisements or other commercial displays. You’ve probably seen them in trade show booths, restaurants, airports, nightclubs, offices, hotels, museum exhibits, and retail shops. That’s right, light boxes are everywhere.

One of the most common uses for light boxes is the commercial advertisement. You see these in large spaces like terminals or outdoors at bus stops. They capture the attention of passers-by and create lasting impressions. The light box pictured below is one of the biggest I’ve ever seen.

One of the most obvious places you’ll see light boxes are along the walls inside and outside of movie theaters. Sometimes lines of light boxes stretch incredible distances, advertising all the movies being shown in large theaters.

In fact, light boxes can be a fun addition to any home and can be used for as many purposes as you can imagine. Sure, you could illuminate a movie poster of your daughter’s favorite movie. But you could also make a custom sign saying whatever you want. I really like the light box below, created at home for home.

Electric motors power everything from tiny electronics to massive industrial pumps. Yet, they all work on the same basic principles. Though AC motors seem ordinary, there are complex activities going on behind the scenes.

The simplest types of motors are three-phase AC motors. They convert a rotating magnetic field into mechanical rotation. The basic parts of an AC motor are the stator, rotor, bearings, drive shaft, and frame. The supply power is connected to coils of wire that are wrapped around laminated iron cores in the stator; the stationary part of the motor. When the coils of wire receive current, they generate a magnetic field known as poles. Each phase of power has the same number of poles; the poles are spaced evenly around the stator.

Historically, speed control of three-phase induction motors was very difficult. The only way to change the operational speed is to change the frequency of electricity supplied. Today, this task is accomplished by use of a variable frequency drive or VFD. This device is made of three main components: a rectifier, a DC-Link, and an inverter. The rectifier takes the incoming AC voltage and converts it to DC voltage that can be used by the electronics in the VFD. The DC-Link then uses capacitors to help smooth out the DC voltage from the rectifier and feeds it to the inverter.

The inverter then converts the DC voltage back to AC voltage. The inverter also controls the output frequency of the AC power by sending precisely timed pulses of DC power at specific voltages to rebuild the AC sine wave.

With a VFD, not only can the output frequency be controlled, but it can be slowly ramped up. This allows for smoother starting and can be adjusted to keep a motor spinning at a specific frequency. VFDs can produce three-phase power from a single-phase source, or even a DC source, to power highly efficient three-phase motors in locations without a three-phase supply. VFDs can also be incorporated into a PLC system to allow for automatic or remote control.

The combination of a VFD and AC motors offers a wide variety of functions and increased efficiency. Basic understanding of these technologies is essential for any electrician.