While the flashlight’s basic design remains unchanged, LEDs are an innovative addition that provide significant benefits. The LED, or light emitting diode, was invented in 1962 by Nick Holonyak for General Electric. It wasn’t until 1999, however, that the Lumileds Corporation succeeded in creating a practical LED flashlight. See how the technologies within this device work together to illuminate your world.
The flashlight is a relatively simple electronic device. In fact, the first patent for the flashlight was issued in 1899. This was only a few years after the first dry-cell battery was invented. All battery powered flash-lights consist of a battery, a spring, a contact strip and a light source. When you turn the switch to the ON position, you complete an electric circuit between the light source and the battery. This circuit causes electrons to drain from the battery and flow into the LEDs. The electrons flow because of a differential between the positive and negative electrodes within the battery.
The circuit itself consists of two conductive strips. The first is connected to the switch and makes contact with the battery. The second strip is connected to the LEDs. When you turn the flashlight off, you break the circuit between these two strips and stop the flow of electrons.
When the electrons reach the LEDs, the LEDs begin to glow with a bright white light. This is because they convert the electrical energy into photonic energy. LEDs are extremely efficient as they only require 60 milliwatts of power to produce light. They are substantially more efficient than normal tungsten-based lights and shine more brightly to boot. However, the light produced by these diodes is dim and must be bounced off of a reflective surface within the lens of the flashlight to produce a strong beam. Once amplified in this way, LED flashlights provide comparable luminosity to standard flashlights at a fraction of the power consumption. Note that not all flashlights are battery powered. Some come with cranks that convert mechanical energy into electricity.
A light-emitting diode is constructed of two-surfaces sandwiched together. The first surface is replete with electrons while the second is electron-hungry. When electrons flow into these layers an energy buildup occurs. The LED—a closed system—must resolve this energy buildup and does so by releasing photons. Manufacturers can control the amount and color of the light produced by altering the chemical makeup of the two semiconductive layers.
Individual LEDs are packaged together on a dye to create a usable amount of light. There are two primary types of LED arrays: pixelated and diffused. Pixelated arrays consist of a layer of visible LEDs while diffused arrays utilize lenses that create a uniform appearance. Diffused arrays simulate natural lighting and are more commonly used in home applications while pixelated arrays see more frequent use in industrial applications.
Some scientists believe that the earliest use of the battery occurred in Mesopotamia more than one thousand years ago. These simple devices consisted of a conductive metal such as copper dipped into a pot of wine. The wine, an electrolyte, built up an electrical charge in the presence of the copper. Whether or not these devices were actually used to store energy is unknown, but the science is sound. The ancient devices may have been used to plate objects with gold, although many scientists doubt this interpretation.
Batteries consist of three parts: an anode, a cathode and an electrolyte. The anode is negatively charged while the cathode is positively charged. The electrolyte serves as a bridge through which electrons flow from the cathode to the anode when energy is supplied to the system. As energy builds up in the battery, an electrical differential occurs. When a conductor connects the cathode and the anode together, by-passing the electrolyte, electrons rush out of the battery, nullifying this differential. In practical terms, the battery is said to be “discharging.” Batteries eventually go bad because the electrodes within them corrode, and because the electrolytes leach into the battery’s casing.
The LED flashlight is an efficient innovation and is particularly useful in survival situations. LEDs last longer and are not as prone to failure as their tungsten-based counterparts. They use less power and can provide a powerful beam when properly amplified by a reflective material.