Since the dawn of time, or perhaps more appropriately, since the night of time as they say in French (la nuit du temps), mankind has needed something to light their way in the dark to see where they are going. Most often it was a treated as a burning stick, generally called a “torch.” The burning torch filled the bill until very late in the 19th century, just over 130 years ago, with the invention of a reliable, easily portable electric light.
Known as an “electric torch” or simply a “torch” in British English and some other languages, in the United States is was dubbed a “flashlight.” This difference of name was not intended to be perverse. The first models actually did flash because the technology at the time did not allow for a steady, unwavering beam. But whatever it is called, this late 19th-century invention completely overturned a practice mankind had counted on for countless millennia.
This is why the flashlight (torch) richly deserves a place of honor on the list of what I like to call “Extraordinary Ordinary Things.”
What Is a Flashlight?
What we think of today as a flashlight first came popular use when mass production began in 1896. It was known as a “dry cell” flashlight. This was because the dry cell battery, created by Danish Frederik Louis Wilhelm Hellesen in 1887, provided electric power with a current-producing paste rather than a liquid. Not containing liquid, the dry cell did not spill and did not easily break. Moreover, it could work in any orientation, i.e. it could be pointed up, down, left, right, or any other direction. This made it the first battery suitable for portable electrical devices, such as flashlights.
Using portable hand-held electric lights offered obvious advantages over burning torches, candles, and oil lamps to shed light into the dark.
- They were odorless, smokeless, and emitted less heat than combustion-powered lights.
- They could be instantly turned on and off, with no need to laboriously start them up again when next needed.
- They could be used with no risk of dangerous accidents.
The first flashlights ran on zinc-carbon batteries. While being paste-based, and therefore safer, the first zinc-carbon did not provide a reliable electric current and required periodic “rest periods” to continue functioning. Moreover, they used energy-inefficient carbon filament incandescent bulbs. The combination of inefficient dry cells and inefficient light bulbs meant the obligatory rest periods had to be impractically frequent. Therefore, these early instruments could light only in brief flashes, hence the American term “flashlight.” The British and certain other nationalities preferred the term “electric torch” or simply “torch.” So today they are called both.
In 1889, Hellesen sold his first batteries to the Danish Telephone Company. The same year Valdemar Ludvigsen, a young Danish chemist, came to Hellesen’s factory to help him further these dry cell batteries. When Hellesen died in 1892, his widow and Ludvigsen took over the company and continued the work of developing more reliable, energy efficient dry cells.
In 1899, English inventor David Misell conceived of what became the classic design for the flashlight. At the back end it consisted of three dry cells placed in a tube. In front of the dry cells was a contact switch connected to a small light bulb. And around the bulb was a curved metallic reflector to concentrate the light coming out of the front end. To turn the device on and off was simply a matter of opening and closing an external switch.
The early flashlight (torch) was not an instant success because of the inefficiencies of the batteries and high electrical consumption of the bulb. Over the next couple of decades, these problems were solved. In particular, the batteries no longer required a rest period, while replacing carbon filament bulbs with tungsten filament bulbs dramatically reduced energy consumption. By the 1920s, the flashlight was rapidly replacing other means of portable, hand-held lighting (flaming torches, candles, oil lanterns, kerosene lanterns, etc.)
Technical advances over the past century have resulted in major changes to the flashlight in two major respects: bulbs and batteries.
There are now two principal flashlight bulbs: incandescent light bulbs and LEDs (light-emitting diodes).
Incandescent light bulbs generally consist of a tungsten filament in a semi evacuated or fully evacuated glass bulb to slow down the rate at which the filament oxidizes (burns up). Other incandescent bulbs are filled an inert gas such as argon, krypton, or xenon. Use of these noble gases reduces both filament oxidation and filament evaporation, making the instrument last longer.
LEDs (light-emitting diodes) are semiconductors that emit light. The types of LEDs used in flashlights are significantly more energy efficient than incandescent light bulbs, and also last longer. LEDS have different light spectra compared to incandescent bulbs. They are made in several ranges of color temperatures and color rendering index. Since the LED has a long life compared to the usual life of a flashlight, very often it is permanently installed.
Dry cell batteries are still the most widely used energy source for flashlights. However, other energy sources are available for specialized purposes, e.g. accumulators or super-capacitors, which can be charged either mechanically by winding them up or automatically by exposing them to sunlight.
Uses of flashlights are generally related to the efficiency of the flashlight measured in “lumens” (luminous efficiency). The lumen is the measure of electrical efficiency now replacing the watt, especially for measuring the efficiency of energy-saving LEDs (light-emitting diodes), which first appeared on the scene in the early 2000s.
Depending on the desired use, modern flashlights can be configured into keyrings and pens, used as headlamps on helmets, mounted rifles, and a variety of other shapes and sizes. And of course, what would be a mobile phone without an incorporated flashlight?
|1–20||Keychain||Finding keyholes, close range use, supplement to dark-adapted vision, walking in the dark|
|30 –100||General purpose||Household use, car repairs, hiking on a trail, cave exploration|
|100 and above||Tactical flashlights||Weapon-mounted lights|
|200 and above||Bicycle headlamps||Light use depends on speed, quality of trail, surrounding light|
|1,000 and up||High powered||Outdoors, search and rescue, caving, night orienteering, high-speed bicycle use, diving|
LED bulbs are more efficient than incandescent bulbs and last longer. Since LEDs are highly efficient at producing colored light, an LED flashlight may contain different LEDs for white and colored light, selectable for different purposes.
For example, colored LED flashlights are used for signaling, forensic examination, or tracking the blood trail of a wounded game animal. Flashlights with a LED are used to enhance night vision. Ultraviolet LEDs are used for detection and inspection purposes such as examining paper currency, checking UV-fluorescing marks on laundry or event ticket tickers, detecting fluorescent dyes added to air conditioning systems to reveal leakage, etc.
Besides conventional dry cells, LED flashlights as energy sources can use accumulators or super-capacitors. Rechargeable models can be charged either mechanically by winding them up or automatically by exposing them to the sun.
If the idea of a wind-up flashlight seems retrograde or ludicrous, you are showing a cultural bias. There are many places in the world where obtaining dry cells or electric current to recharge a flashlight is still a major problem. Mechanical flashlights also have an important role to play during natural disasters when normal electric current is not functioning. For example, mechanically powered flashlights were distributed by aid organizations to survivors of the 2010 Haiti earthquake since electric power was lost for a long period.
There are several types of mechanical flashlights using different motions to generate electrical energy, e.g. squeezing a handle, winding a crank, or shaking the flashlight itself. Mechanical flashlight also uses different means to store the mechanically generated electrical energy, e.g. spring, flywheel, battery, capacitor.
Some people promote mechanical flashlights as a partial solution to perhaps the most menacing disaster of all—manmade climate change. Conventional flashlights are considered “non-green” because their disposable batteries contain heavy metals and toxic chemicals that end up in the environment.
A much less common type of flashlight than either the incandescent or LED is the high-density discharge lamp (HID). This special member of the flashlight family uses a mixture of metal halide salts and argon as filler. It also lasts longer and is more shock resistant. On the other hand, it is much more expensive. A HID lamp does not come on instantly—it requires a few seconds to warm-up before reaching full output. A 35-watt HID lamp typically produces more than 3,000 lumens.
Flashlights and Computers
One of the most common uses of flashlights today is on those miniature hand-held computers known as smartphones. There are two basic applications: 1) as a conventional flashlight for seeing in the dark, 2) a flash for taking pictures. The structure and technology are somewhat different for the two applications. When the flashlight was added to smartphones, it got an enthusiastic customer response, and today it is one of the most used features.
While I was writing this blog, a friend asked me “Why is a magnifying glass used as a search icon rather than a flashlight?” This is a good question. The best answer I was able to find is that it is largely a matter of custom.
Decades ago, some pioneering program developer liked the idea and it stuck. Apparently, they were thinking of the culturally ingrained image of a detective searching for clues by looking through a powerful magnifying glass. However, it could be argued that a flashlight icon would be more appropriate. Why? Because a magnifying glass is useful only with the aid of natural or artificial light, in the dark it is useless. Although a flashlight is inferior to a magnifying glass in the light, in the dark it is indispensable.
But this is an almost juvenile dispute. Professionals who design icons for computers have considerably more sophisticated arguments for or against the magnifying glass image. If you wish to enter the discussion, visit: https://www.nngroup.com/articles/magnifying-glass-icon. Or insert “why is a magnifying glass used as the search icon?” into your internet browser.