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Reference Guide for Commonly Used Terms

What’s the difference between AC and DC electricity? What makes amps different from watts or volts? How do lux, lumens and candelas relate to one another? Browse our battery terms reference glossary for the answers to these questions and more.

Contact our online battery sales team today with any questions about the batteries or flashlights we carry.


AC Adapter

Since the vast majority of household electronics require DC current to operate correctly, an AC/DC Adapter must be used to convert 120V 60Hz AC power from a standard US wall socket to the appropriate DC voltage.

AC Adapters can be internal on large electronics, such as TVs, desktop computers and some game systems, or external on smaller devices, like cell phones and laptops.

AC Adapters use a small transformer to convert wall outlet power to the desired voltage and frequency.


There are predominantly two types of currents used to deliver electricity in any form—from a batteries, power plants, solar cells, etc.

In DC, or direct current, current always flows in the same direction between positive and negative terminals. In AC, or alternating current delivery, the direction the current travels reverses many times a second. 60 times per second in the US, to be exact.

Thomas Edison’s original 19th Century power plants relied on direct current to transmit electricity. Besides the greater dangers posed by DC power, he could only deliver electricity up to about a mile from the generator before losing power.

Based on patents published by Nikola Tesla, George Westinghouse began building AC power plants in the late 1880s capable of delivering electricity hundreds of miles away with little power loss.

AC power plants use transformers to change the voltage of electricity. Higher voltages allow transmission of greater wattages of electricity over longer distances, which are then transformed into lower voltages for delivery to homes and businesses.

The standard wall outlet in the United States delivers 120V, 60Hz AC power.

Sizable parts of Boston and New York still relied on DC power up until the 1960s, and ConEd of New York didn’t officially end DC power generation until 2007.

Batteries deliver DC power to devices. Most household electronics rely on DC currents for reliable functionality, and the relatively low voltages of batteries are able to deliver DC power safely and efficiently.


Alkaline batteries are generally a primary (non-rechargeable) power source with internal zinc-manganese dioxide (Zn/Mn02) chemistry where zinc is the negative electrode and manganese dioxide the positive electrode.

Until the 1990s, most alkaline batteries contained mercury. Energizer® brand alkaline batteries were the first mercury-free batteries made widely available on the market.

Leaking alkaline batteries will create potassium hydroxide, which causes irritation to the skin, eyes and lungs. You can prevent leaks by following simple alkaline battery care guidelines.


In electrodynamics, amperes, or amps, measure the amount of electricity passing through a particular point in a current. Amps are the home electricity equivalent to water flow in home plumbing and shouldn’t be confused with voltage which is the electrical equivalent to water pressure.

In the case of electric shock, the amperage of electricity entering your body will typically have the greatest effect on your chances of survival.



A candela is roughly equivalent to the intensity of light given off by one candle. Different flashlights produce different candela outputs, often for specific purposes.

Streamlight produces a wide range of professional flashlights which output candela levels from several hundred (typically soft flood lights) up to tens of thousands (high-powered scene and spot lights).

Candela ratings on flashlights are most useful when you are concerned with the brightness of a focused beam, as opposed to total light output (which is measured in lumens).



Hertz is a measure of frequency in electrical systems. A typical wall outlet in the US provides 120V at 60Hz AC, meaning the current changes direction, or “cycles,” 60 times every second. Small transformers contained within an AC Adapter can change both the voltage and frequency of electricity delivered to household appliances.

This frequency shift is necessary in order to use many international appliances in the US, as not all countries use a 60Hz standard. For example, most European nations have power grids conforming to a 50Hz standard.



LEDs, or light-emitting diodes are compact electroluminescent devices capable of delivering very bright outputs using relatively low electrical wattage compared to other bulbs.

Streamlight C4® LED flashlights deliver high performance and excellent battery life. The C4 LED bulb is shock-proof, unlike most traditional bulbs, and will run up to 50,000 hours before it needs replacing.

LED technology is also used in a variety of consumer electronics, including as screens for televisions and cell phones and infrared remote controls.


Lithium polymer, or Li-poly, batteries are a specific type of lithium-ion rechargeable battery. Originally, Li-poly referred to experimental batteries which replaced the standard liquid electrolyte with a polymer electrolyte, allowing thinner leak-free designs. This technology has yet to become commercialized.

The Li-poly batteries you do see on the market still have a liquid electrolyte, however it is contained within a plastic polymer pouch.

For all practical purposes these Li-poly batteries are not significantly different than other Li-ion batteries on the market, and the terms is oftentimes interchangeable.

Lithium Battery

The term “lithium battery” is something of a catch-all for numerous types of primary battery chemistries using lithium or lithium compounds as an anode. Lithium has a very high energy density, giving them long life, but also high cost to manufacture.

The vast majority of consumer primary lithium batteries are composed of lithium-manganese dioxide (Li/MnO2 or “CR”), which is very similar to the typical alkaline battery chemistry of Zn/MnO2.

Another popular lithium battery chemistry is lithium-iron disulfide (Li/FeS2 or “FR”). Energizer® Ultimate lithium batteries use iron disulfide chemistry because they match the typical 1.5V output of standard AA and AAA alkaline batteries, with a far greater lifetime both in storage and in high-discharge use.

You should never attempt to recharge primary lithium batteries, as volatile lithium is prone to leaking, igniting or exploding.

Lithium Ion

Lithium Ion or Li-ion

Unlike primary lithium batteries, lithium-ion or Li-ion batteries are rechargeable. Li-ion batteries use stable lithium compounds as opposed to pure lithium metal. Lithium ions provide power by traveling from the negative electrode to the positive electrode during discharge. Recharging the battery causes these ions to reverse course back from positive back to negative.

Li-ion batteries are the nearly ubiquitous choice for cell phone and laptop batteries due to their high energy density, slow discharge when not in use and the fact they have no memory effect.

Despite their popularity, Li-ion batteries should be handled with care. Li-ion batteries use a flammable electrolyte and are kept under pressure.


Lumens are a measure of total light output of a flashlight. Lumens should not be confused with candela which is a measurement of a focused beam’s brightness.

When choosing a Streamlight professional flashlight, knowing the intended use for the flashlight will determine whether you should focus more on lumens or candela output. Flood and scene lights are best measured by lumen output, and peak candela intensity is less important when trying to illuminate a large area.


Lux is a measure of lumens is a given area. 1 unit of lux is equal to one lumen per square meter. It is used to measure the intensity of illumination on a surface.



Nickel Cadmium batteries are rechargeable.


Nickel Metal Hydride