How Does a Spotlight Work?

In their most basic form, spotlights are basic electrical circuits. A power source--which may, depending on the model of the spotlight, be either alternating or direct current—connects through a switch to a high intensity light bulb. When the switch is moved into the “On” position, a mechanism inside the switch completes the electrical circuit and allows current to flow from the power source, through the lamp, and back to the power ground path. A filament inside the bulb resists the flow of electricity and, as the electricity forces its way through, begins to glow. In some very high efficiency spotlights, the electrical current feeds a small circuit board that, in turn, illuminates a collection of high intensity light emitting diodes (LED) to produce light.

Although the flow of electricity illuminates a bulb inside the spotlight, the bulb alone is rarely sufficient to produce the large amounts of light for which spotlights are renowned. To amplify the light produced by the bulb, the concave area around the bulb is coated in highly reflective, angled material. The angles within the material catch and reflect the light from the bulb, amplifying its effect. This reflective area, which is usually comprised of aluminum-coated plastic, also serves to redirect the light into a steady beam, augmenting the function of the lens. Depending on the size of the spotlight and reflectivity of the coated area, a single bulb or small collection of LEDs can be amplified to 10,000 or more lumens (125,700 candle power).

While the bulb and reflective area of the spotlight produce ample amounts of light, the natural tendency of light beams is to scatter into a broad, unfocused area. Because scattered light waves would create an ineffective spotlight, manufacturers usually cover the bulb and reflective area with a special plastic or glass lens. Much like the lens of a camera or eyeglasses, the lens on a spotlight directs light from the source into a single, focused path. Depending on the make and model of the spotlight, the lens may be adjustable, allowing the user to switch from a dimmer light that covers a very large area to a very bright, focused light that is concentrated on a small surface.