▣ The safe light in your hand, the flashlight
A flashlight is a portable lighting device that emits light using a bulb and batteries. In the United States, it’s called a flashlight, while in the United Kingdom, it’s referred to as a torch. The invention of the flashlight has revolutionized human life.
▣ The Birth of Flashlights
So, how did the flashlight come to be? The birth of the flashlight began with an idea by Joshua Lionel Cowen to install lights in flowerpots for decorative purposes. He sold this idea to a company manufacturing Christmas lights and other electrical products, and British inventor David Misell further developed Cowen’s idea, inventing the model similar to today’s flashlight in 1898.
Despite using a short-lived carbon filament, it gained immense popularity. The tungsten filament bulb, introduced in 1910, significantly improved the brightness and energy efficiency of flashlights. Moreover, advancements in batteries quickly replaced oil lanterns with flashlights. An object that emits light by itself is called a “light source,” with the bulb serving as the light source in flashlights. Flashlights are classified based on their light sources.
The most basic flashlight uses an incandescent bulb, known as an “incandescent flashlight.” The “halogen flashlight” utilizes a bulb filled with halogen gas, providing longer usage time and greater brightness compared to incandescent lights. The “xenon flashlight” employs a bulb filled with xenon gas. Xenon lights are mainly used for automotive lighting and are also used for lighting in night photography and video shooting due to their natural, sunlight-like color rendering. However, they are expensive and less practical. Recently, there has been an increase in products using LEDs and rechargeable batteries, known for their high energy efficiency.
▣ Structure and Principle of Flashlight Illumination
In traditional flashlights, incandescent bulbs are used, containing a filament wire placed within a glass bulb or vacuum tube. The positive and negative ends of the batteries are connected directly to the bulb, and when electricity flows through the bulb, the filament inside heats up, producing light.
While light should ideally spread in all directions around the bulb, the light emitted from a flashlight travels in a single direction. This is achieved by employing a reflective coating around the bulb, often in a cone shape, to concentrate the light. The reflective coating serves to redirect light attempting to scatter in other directions, focusing it in one direction. However, incandescent bulbs can become unusable if they receive excessive current or are used for prolonged periods, causing the filament to burn out. Hence, LED flashlights, which do not produce heat like incandescent bulbs, are widely used nowadays.
LEDs (Light-Emitting Diodes) are semiconductor devices. By doping a semiconductor, impurities are introduced to increase its electrical conductivity. This creates an excess of electrons in the N-type semiconductor near the insulator and generates “holes” in the P-type semiconductor. When these are combined in a diode, particles with negative charge, such as electrons, naturally move from areas with more electrons (negative) to those with fewer (positive). As a result, when electrons move from one side of the diode to the other, light is emitted. Depending on the materials used in the semiconductor, LEDs can emit light of various wavelengths.
▣ When Light is Needed Anywhere, Anytime: Flashlights
Flashlights are most useful during travel, camping, and other outdoor activities. Not only do they provide illumination for freely navigating dark nights, but they also prove invaluable in emergencies such as being lost in the wilderness. Smartphones, primarily reserved for emergency communication, are impractical for use as lights due to their high battery consumption. This is where a flashlight shines. While flashlights of the past may have been bulky and emitted low light, today, compact and durable models boasting brightness levels and beam adjustments comparable to motorcycle headlights are readily available.
Flashlights utilized by search and rescue teams for nighttime operations boast an intensity of around 10 million candlepower. To put this into perspective, imagine it being brighter than turning on 1,000 fluorescent lamps. Such intense light, seemingly unnecessary for daily life, is also used as a self-defense tool. Shining a light of 1,000 lumens or more directly into someone’s face can be blinding, making it impossible for them to see without shielding their eyes. Additionally, incorporating a strobe mode, which induces visual confusion, makes the flashlight a formidable tool for self-defense or subduing criminals. Furthermore, flashlights are designed with a “strike bezel,” a rugged, pointed crown encircling the head or tail, allowing them to be used as an impact weapon. However, it’s important to remember that flashlights are only one tool among many for creating a gap in a threatening situation and should not be solely relied upon for self-defense.
