How Do LED Flashlights Work?

Date: August 26, 2020

Posted By: James Burry

There is a difference between knowing how to work something and how it works. For flashlights, working one requires making sure you have batteries, that the lights work, and knowing how to turn them on. But how does an LED flashlight work?

An LED, or light-emitting-diode flashlight, works by moving electrons to create light. A semiconductor material, such as silicon or gallium, is modified so that current can flow through it. The light is created by modifying the path of electrons in the semiconductor.

Understanding how an LED works requires some basic knowledge of chemistry, electricity, and light. Knowing how they work will help you understand why they provide more light with greater efficiency than incandescent bulb flashlights.

What Is an LED Flashlight?

Traditional flashlights use an incandescent bulb powered by a battery to provide light. The current from the battery heats the filament wire inside the bulb, causing it to glow and give off light. Incandescent bulb flashlights have been in use since 1899, but they are inefficient. The heat from the bulb is wasted energy, and turning the flashlight on and off frequently causes the filament to burn out.

Light-emitting diode (LED) flashlights, which were first sold in the early 2000s, rely on the movement of electrodes to create light. Because of the way they generate light, LED flashlights use less power than traditional or halogen flashlights. At the same time, they can generate more light.

LED lighting has been in use since the 1960s--computers, traffic lights, cars, TVs, and remote controls all use LEDs. Before they could be used in flashlights, several technical advances were required.

Finally, incandescent flashlights are less expensive than LED lights; however, both the batteries and bulbs of an LED last much longer. When you factor in the replacement costs, LED flashlights are less expensive in the long run.

How Do LED Flashlights Work?

The first LED was invented by accident in 1961 by James R. Biard and Gary Pittman, while working on developing semiconductors. Shortly after that, IBM began to use them in punch-card readers. Although LEDs were used widely in numerous industries, it wasn’t until 1999 that the first LED flashlight was sold.

So, how do LED flashlights create light? They do so through the movement of electrons through a semiconductor. But what is a semiconductor, and how does the movement of electrons create light? To explain that, we will start with semiconductors.

What Is a Semiconductor?

A semiconductor is made from a substance that is a poor conductor of electricity. Impurities added to the material allow it to be manipulated to conduct electricity in some instances but not others.

Silicon is a commonly used element (as in Silicon Valley), although another element, gallium, is used to manufacture LEDs. The process, however, is the same. By themselves, silicon or gallium won’t allow electricity to flow through them. However, when other elements are added to it, silicon can conduct electricity—hence a semiconductor.

How Does a Semiconductor Create Light?

The first step in creating a light-emitting diode involves adding impurities into the silicon, also known as doping. Two kinds of doping—N and P--are required for the diode.

In N-type doping, elements with five electrons, such as phosphorus or arsenic, are added to the silicon. These electrons have a negative charge.
In P-type doping, elements that have 3 electrons, such as boron, are added to silicon, creating a positive charge.
When P-type and N-type silicon are joined, it becomes possible for the silicon to become a conductor of electricity. A battery that is properly connected to the diode (positive to positive) allows a current to flow between the P-type and N-type silicon.
The current that flows through the junction between the P-type and N-type can then be used to generate light.

A transistor is created by using three layers of a diode. A silicon chip can hold thousands of transistors, thus creating the silicon chips that run our computers and a multiple of other electronic devices. None of those would be possible without the diode.

How Does the Diode Create Light?

To understand this, a bit of background about atoms and photons is required. Light is created from atoms into little packets of energy that can move but contain no mass. When these packets are combined, they form photons--basic units of light.

We know that atoms consist of electrons that orbit a nucleus. If left undisturbed, the electrons remain within their orbit. However, if electrons are forced to move into a lower orbit, they create photons.

All diodes release photons, but those made purely from silicon create low-frequency photons or infrared light that our eyes can’t see. That is the reason that you cannot see the light that comes from a remote control.

For us to see the photons, silicon needs to be doped with materials that create more energy. A variety of colors can be generated from LED lights by using different materials. The common element is gallium, but other elements create a broad spectrum of color options:

Red and Infrared LEDs contain aluminum gallium arsenide
Yellow and Green contain gallium phosphide
Orange and Red high-brightness colors are created with aluminum gallium phosphide
Blue, green, and ultraviolet lights contain indium gallium nitride

Not All Diodes Release Light Effectively

Because diodes do not emit light effectively, so they are designed to have the photons reflect away from the resin body the diodes sit on. Also, the transparent plastic epoxy shell that protects the diode is designed to concentrate the light.

Since LEDs are solid-state components, they create “cold” light instead of the “warm” light of incandescent bulbs. Most of the energy generated from an incandescent light is not light, but heat. In an LED, however, almost all energy is emitted as light waves. That is one reason that LEDs are far more efficient than “regular” light bulbs.

Even though LEDs create cold light, heat can still be a problem with LEDs. The junction’s temperature rises as current passes through the diode. This can lead to changes in the light’s color, reduced efficiency, and a drop in light output.

To combat this, light engineers use adhesives, base plates, and pads that isolate the excessive electricity and conduct it away from the diode. Design features in the case, such as ridges, increase the surface area, allowing more heat to dissipate. Removing this excessive heat is something we will touch on later in a discussion on extremely bright LED lights.

Regulating LED Lights

Incandescent and cheap LED flashlights are powered through a direct drive, meaning powered directly by the battery. This direct method is straightforward, but it also means that light output is based on how much juice a battery has. As your battery runs down, the flashlight dims.

Most LED flashlights have a driver that regulates the voltage the lights receive. These drivers can perform a variety of functions:

Reduce or amplify the voltage that comes from batteries
Control levels of brightness
Serve as the interface between the lights and the battery

Drivers are classified by their function. For example, a FET driver uses a transistor and microprocessor to regulate current. A boost, or step-up circuit, increases the input voltage, so it matches the output. Flashlights that can work with either one or two batteries use a boost circuit.

A buck circuit reduces the voltage, and it is typically used in lights that have cells connected in series. A buck-boost circuit can boost and reduce voltage. Although circuits such as the AK47-Mode are available for sale, they are bought by enthusiasts and collectors who want to modify their flashlights.

LED Lights and Lumens

Lumen is a word that gets thrown around frequently. The more lumens, the brighter the light—but what exactly are lumens? Let’s find out.

The simple answer is that a lumen is a way to measure light output. So candles will claim they emit a certain level of lumens. However, measuring brightness is not as simple as it might sound.

For example, a lumen is only one out of five ways to measure light. Here are all five:

Intensity. Candela is the unit of measure that describes the brightness of the light as it moves in all directions. Candela is measured as the source of light.
Flux. Flux or lumens refers to how the light flows in the air. Lumens, then, is not a measure of the brightness of the light.
Illuminance. This refers to the density of light on the surface of an object. It is measured in foot candles—how much light lands on a square foot of an object.
Existence. A measure of how much light is reflected from an object.
Luminance. A measure of how much light is reflected at different angles.

Your perception of the brightness a flashlight puts out is determined not only by lumens but also by other factors. For example, a flashlight with 900 lumens and a standard lens will shine more brightly on an object in the distance.

However, changing the lens in a flashlight to create a broad beam affects the luminance. The flashlight will still give off 900 lumens, but the floodlight effect means you won’t be able to see distant objects as well, but a larger area closer to the light source will be illuminated.

Batteries As the Power Source

With a couple of exceptions, LEDs are powered by batteries. Your model may recommend a particular battery type, but it's good to understand the properties of different batteries if the kind you want isn't available when you need them.

Alkaline batteries are commonly used. Depending on how you will use your light, they are acceptable batteries. Alkaline batteries can keep their charge for several years, so if you rarely use a flashlight, then they are a good choice. If you frequently use high-performance flashlights, then you should look for a different type of battery.
Carbon-zinc batteries. These are rarely sold separately. However, the batteries that come with budget flashlights are often carbon-zinc.
Lithium batteries. These batteries can hold their charge for up to 10 years. If you have a high-performance flashlight, then lithium is a better choice. High-performance lights use more current, and lithium batteries store more energy, making them a better choice. Lithium batteries also handle temperature changes better.
NiMH batteries. One advantage of NiMH (nickel-metal hydride) batteries is that they are recyclable. Both lithium and NiMH batteries cost more, but Lithium batteries cannot be recharged (lithium-ions can—more on that in a bit). If you use a flashlight frequently, these might be a good option because they can be recharged. When buying NiMH batteries, make sure they are low self-discharging batteries.
Rechargeable batteries. Most LED flashlights can use rechargeable batteries. The one caution is that as batteries get recharged, they lose voltage. Since LED lights are more finicky when it comes to battery voltage, it’s a good idea to keep your eye out for that.
Built-in rechargeable batteries. If you are in the market for a new LED flashlight, a model with rechargeable batteries built in has several advantages. The most obvious one is it will save you money over the long term. A second is convenience. A battery with built-in charging capabilities means one less piece of equipment to carry. If you purchase one that has a USB option, you increase the ways it can be recharged. However, these types of flashlights are not recommended for long trips or emergency situations where you might not have the ability to recharge them for long periods of time. If you can’t swap out the battery with a fresh battery, then your rechargeable flashlight is worthless after you drain the battery once and can’t recharge.

Why Should I Buy an LED Flashlight?

Since LEDs are more expensive, it is reasonable to ask if they are worth the extra expense. We can think of many reasons why LEDs are worth the extra cost, but since we’re talking money, let’s start there.

They Last Longer

Most LED flashlights are rated to last at least 50,000 hours. If you keep the flashlight on for 24 hours, you will get over 2,000 days or five years of light before the bulb gives out. An incandescent bulb is rated to last 1,000 to 2,000 hours, so 25 light bulbs would be needed to outlast an LED.

This LED Replacement bulb costs around 10 dollars while an 8-pack of replacement lights for a Ryobi flashlight runs around 12 dollars. Multiply that by three, and your incandescent bulbs will cost 36 dollars.

Ironically, the more you turn an incandescent light on and off, the quicker it burns out. That’s because the repeated heating and cooling of the filament causes it to expand and shrink. The expansion leads to tiny cracks that eventually cause the filament to break. The Centennial Light in Livermore, California, was installed in 1901 and still works.

They Have a Longer Battery Life

Of course, you can’t run a flashlight for five years on one battery. LEDs require less power, which means fewer batteries as well. The batteries in an LED flashlight will last between 6 and 10 times longer than those used in an incandescent battery. So an LED battery will save you money on bulbs and batteries. But that’s not all.

We call these devices flashlights because the first lights had to be turned off repeatedly. This was due to the nature of the batteries at that time as they could not provide electrical current for more than a few minutes.

They Are More Durable

Anytime a regular lightbulb is dropped, there is a good chance the filament in the bulb will break. Since a LED does not have a bulb, that cannot happen. And since LEDs are lighter, they hit the ground with less force.

What Features Should I Look for in a LED Flashlight?

The key features people usually think about when selecting an LED flashlight—besides price--are cost, light output, battery requirements, and size and weight. There are other features you might want to consider, including some you might not realize are available.

Beam

A broad beam lights up a wide area but for a short distance. These are excellent for camping or taking a walk. A flashlight for home use generally has a broad beam.
A focused or narrow beam is used for long-distance lighting when an object in the distance needs to be illuminated. These are used by law enforcement, hunters, and cave explorers, among others.
A combined beam such as on the BAMFF Tactical DUAL LED Flashlights is perfect if you want a flexible light. They are ideal for outdoor activities, such as hiking, and can also be used in rescue operations.

Some flashlights provide the user the option of controlling how much of a broad or focused beam you want.

Output

A flashlight that starts off bright and gives off less light the longer it is used is an unregulated light. A regulated flashlight never reaches peak brightness, but the regulation mechanism allows the light to remain level. Additional circuitry is added to a regulated light that lets it better control the current flow between battery and lights.

Luckily, most LED lights are regulated, so this is something you don't have to worry about. A flashlight that is regulated will typically describe its light output as having two separate lumen outputs, such as 1,000 lumens for two minutes, and then 500 for however long the battery will last.

For example, the Mobile Task Light by STKR will emit an astounding 1200 lumens the entire time the light is powered. It will never dim as the battery drains. This is great as the user knows they will always be getting the full potential of the LED. The light is designed with a smart driver that regulates the battery to get the most run time possible. It also features several power modes so you can extend the battery life by selecting a lower power setting.

Settings

For everyday use, a battery with a single setting is probably all one needs. Some flashlights have additional settings:

Multiple. These allow the user to change the intensity of the beam. This is an excellent option that allows the user to match light output to the situation. How to change these settings varies between models.
Specialized. Some lights come with an SOS or strobe light feature.
Programmable. With programmable flashlights, you can make your flashlight turn itself off, change brightness, or program a secondary light level. Some lights have programming features built-in while others come with USB cords so that programming can be done on a laptop and then transferred to the flashlight.

Controls

There are multiple options for how lights can be turned on. Some have a simple on/off slider switch or a push-button. A slider can have a safety lock that prevents that light from coming on, a good feature to have if the light is often transported.

Lights can also be turned on with a rotating bezel. These require two hands but can provide control over light output. Flashlights with a push button in the base of the handle are popular with law enforcement. Another popular feature is a silent momentary button function that allows the light to be turned on and off instantly by pressing and releasing the pressure switch. Fully clicking the switch allows the light to remain on.

Accessories

Flashlights come with multiple accessories that increase their versatility.

Carrying options. Some flashlights are small enough they can be carried in a pocket. Lanyards are a popular method for carrying them, but you can also find a variety of holsters and belt clips that let you bring a flashlight along without having to carry it. You can even find a running belt designed to hold a small flashlight.
Filters. You can find numerous color filters and diffusers. Green and red filters increase nighttime visibility. If you have a focused beam, a white diffuser broadens the beam. A blue filter is excellent for tracking blood in the dark.
Mounts. If you need to mount a flashlight to a rifle or handgun, those are available. A flashlight can also be attached to binoculars. These mounts are used by hunters and in law enforcement. Cyclists can find mounts so they can use their flashlight as a nightlight. Camera stand mounts help photographers get a perfect shot.
Remote Switches. These switches work in conjunction with the mounts described above. Mounting a flashlight on a gun like a rifle or shotgun puts it out of reach to turn the light on or off without letting go of the weapon. That's where a remote switch comes in. They can usually replace the tail switch push button with a wired switch that can be mounted near the trigger.
Chargers. Rechargeable LED flashlights are an environmentally friendly and more convenient way to keep a battery fully charged. Your battery might allow for USB charging, 12-volt car chargers, solar chargers, and more. Check compatibility before buying a charger—magnetic chargers, for example, are limited to certain models.
Window Breakers and Strike Bezels. Again these products are primarily for law enforcement and self-defense. Window breakers allow firefighters to safely break a window, and strike bezels turn a flashlight into a self-defense weapon.

Determining the Quality of a Flashlight

Manufacturers of high-quality flashlights use the ANSI FL1 Standards to rate their flashlights. These standards are based on agreed-upon testing methods. For example, manufacturers agree to use similar methods to measure lumens and beam distance.

Other qualities that are measured include:

Run time. Manufacturers measure light 30 seconds after the flashlight is turned on until it reaches 10% of that first measurement.
Intensity. Along with lumen and beam distance, manufacturers measure the brightest point in a beam of light.
Impact Resistance. Manufacturers measure the height from which their light can be dropped six times without visible damage and still work.
Water Resistance. This rating is determined by how well a flashlight functions after a set amount of water is sprayed against it.
Waterproof. In this test, the light is submerged. The depth rating includes both the depth and length of time.

Both water resistance and waterproof tests are completed after the impact resistance test to simulate real-life conditions.

Look for FL 1 standard ratings on flashlights if you want to compare how well flashlights compare to one another.

What About Self Power Generating LED Flashlights?

Even though having a battery-free flashlight sounds like an excellent idea, it's good to look at the pros and cons before choosing one.

Hand-Cranked Flashlight

A hand-cranked flashlight contains a rechargeable lithium-ion battery. The handle turns the generator, which recharges the battery. A minute of cranking typically gives about 30 minutes of light. However, most of the lithium-ion batteries are rated for 500 charges.

Some hand-crank batteries now include a solar charger. However, unless the manufacturer indicates how many charges the battery can hold, the flashlight has a limited lifespan. Technically, hand-cranked flashlights are not battery-free.

Squeeze Flashlight

A squeeze flashlight is a truly battery-free option. Squeezing the handle of these lights turns a flywheel. The energy from the flywheel goes into a small generator, which generates a current to an LED. Non-LED versions of squeeze flashlights were used during World War II.

Faraday Flashlight

Another battery-free LED light is a Faraday flashlight. Commonly referred to as a shake flashlight, these batteries rely on Faraday’s Law of Induction, which, broadly speaking, is creating electricity using magnets. Shaking a Faraday flashlight horizontally causes a rare-earth magnet to create a current as it moves through a copper wire coil.

To get five minutes of usable light, the battery needs to be shaken vigorously for around 30 seconds. If you want a flashlight that will always give you several minutes of light and make a great conversation piece, a shake light is worth looking into.

Be on the lookout for counterfeit shake lights that run on a small lithium battery. For example, this Shake Light Flashlight lists its NiMH battery as having 10,000 charges. A true shake light should not have a battery.

Can You Make Your Own LED Flashlight?

Anyone can make a flashlight LED or incandescent. If you have a bulb, a battery, and some wires, you can build your own flashlight. Energizer, for example, provides directions for making a simple flashlight using a bulb, battery, wires, and a cardboard tube.

However, a bulb flashlight does not allow for much tinkering. An LED, on the other hand, can be modified in numerous ways:

LEDs. Both the number of LEDs and their strength can be modified.
Driver. Drivers make sure that the batteries and LEDs interact correctly. Playing around with different drivers allows you to change the size and type of batteries and LEDs.
Programming. As we discussed earlier, LEDs can be programmed, leading to additional tweaks.

Google "building LED flashlight," and you will find hundreds of pages with DIY flashlight designs. Some focus on how to build one cheaply while others focus on lumens, such as an article about a homemade 72,000 Lumen flashlight.

Bottom Line

LED flashlights are both simple and fascinating at the same time. Because they are created with semiconductors and solid-state design, these flashlights create more lights using less energy. They last longer and are more durable. There is more to LED flashlights than how many lumens they give off. Intensity, type of beam, and the addition of lenses make them adaptable for many uses, from camping and hunting to law enforcement and self-defense.

When shopping for an LED flashlight, be aware that there are a lot of options on the market. Although many look nearly identical, there are high quality and low-quality flashlights on the market. Amazon is a sea of non branded flashlights offering unbelievable performance specs at a low cost. They are unbelievable because, well, most are not ethical in their marketing and performance specifications.

In the long run, you will be smart to avoid cheap, non branded, direct from China flashlights and stick to quality known brands, such as STKR, Surefire, Streamlight, Nebo, etc. These types of companies are the true innovators. They create quality products and stand behind their warranties. They may cost a little more, but if you are really ever in need of a good light (power outage, emergency, roadside, etc), you will want a flashlight you can depend on.