Flashlight packaging is full of big numbers. One light promises thousands of lumens, another boasts a beam distance of hundreds of meters, and a third lists a candela figure that looks like a typo. These numbers are not marketing fluff, but they do measure different things, and the brightest light on paper is not always the right light for you. This guide explains what each figure means, how they are tested and how to use them when you shop.
We lean on published material from Fenix's glossary of flashlight terms and the company's overview of the American National Standards Institute (ANSI) testing standard, because the examples are concrete and the definitions are clear.
Lumens measure total light
A lumen is a measure of the total amount of visible light a flashlight or headlamp emits. Think of it as the size of the bucket of light, regardless of where that light goes. Higher lumens mean a brighter light overall, so a light rated at 1,000 lumens floods a room more than one rated at 100.
More is not always better, though. Fenix notes that a light in the range of 100 to 300 lumens is plenty for everyday tasks such as finding something that rolled under a car seat. For a pocket light used around the house or on a walk, a modest output covers most of what you will actually do with it.
Candela measures intensity
Candela measures luminous intensity, which describes how concentrated the light is in a particular direction. If lumens are the size of the bucket, candela is how tightly the water is aimed. A light that focuses its output into a narrow, intense beam will have a high candela figure, and a light that spreads the same output into a wide flood will have a lower one.
As a rule, the higher the candela, the farther a light can throw its beam. Fenix gives a useful comparison between two of its large rechargeable lights. The LR35R produces up to 10,000 lumens with a peak intensity of 63,200 candela. The LR50R produces 12,000 lumens, only 2,000 more, but reaches 225,700 candela, enough to throw light 950 meters, or 3,117 feet. Similar output, very different reach, because one is built to flood and the other to throw.
Beam distance is calculated
Beam distance sounds like something measured with a tape, but under the ANSI FL1 standard it is calculated from candela. The standard defines beam distance as how far from the light the beam falls to 0.25 lux. The formula is the square root of the peak beam intensity in candela divided by 0.25.
That means beam distance and candela always move together. When you see two lights with similar beam distances, they will have similar candela figures. It also means beam distance tells you where the beam becomes dim, not where it becomes useful, so you will see clearly over a shorter range than the number suggests.
How ANSI FL1 tests a light
Before a shared standard existed, brands measured their lights in different ways, which made comparisons nearly meaningless. The ANSI FL1 standard set common methods for six things: light output, runtime, beam distance, peak beam intensity, impact resistance and water resistance. According to Fenix's summary of the standard:
- Light output is reported in lumens as the average of three samples, measured between 30 seconds and 2 minutes after the light is turned on with fresh batteries.
- Runtime is the time from that initial reading until output drops to 10 percent of its starting value. It is measured at the highest mode unless the brand says otherwise.
- Peak beam intensity is measured with a light meter placed 2, 10 or 30 meters from the lens. The brightest reading in lux is multiplied by the distance squared to give candela.
- Impact resistance requires each sample to survive six drops, one for each face of an imaginary cube, from at least 1 meter onto a solid surface with no visible cracks and full function. Ratings above 1 meter are rounded down to the nearest whole meter.
- Water resistance covers three separate tests for splashing water, temporary immersion and continuous immersion.
The 10 percent runtime rule is worth understanding. The clock keeps running until output falls to a tenth of where it started, so the runtime figure tells you how long the light keeps producing useful light, not how long it holds its very brightest level.
Ingress protection ratings
Many flashlights also list an ingress protection (IP) rating, a code that describes how well the body resists dust and water. Fenix explains these ratings in its glossary, and uses its PD25R pocket light as an example. That light carries an IP68 rating and is rated to survive immersion to 2 meters for 30 minutes. If you plan to use a light in rain, on a boat or around a pool, the IP rating matters more than an extra few hundred lumens.
Matching specs to real use
Here is how to put the numbers to work:
- Around the house and on walks: look for a compact light with 100 to 300 lumens on its main modes. Candela matters little. Our posts on the Mini Maglite and the Streamlight MicroStream cover this category.
- Everyday carry: a pocket light with a useful low mode, a strong high mode and a good IP rating covers most needs. The Olight Arkfeld Pro is one example of a flat light built for the pocket.
- Trails and property checks: look for higher candela so the beam reaches down a path or across a field.
- Search and rescue or long range spotting: candela is the key figure. Fenix's own flashlight questions page points to the LR50R's long throw for search and rescue work.
Pay attention to runtime at the mode you will actually use. If you want a broader overview of pocket tools to pair with a light, our multitool roundup is a good next stop.
The short version
Lumens describe how much light you get. Candela describes how tightly it is focused and therefore how far it reaches. Beam distance is calculated from candela. ANSI FL1 makes those numbers comparable across brands, and the IP rating tells you how much weather a light can take. Read all of them together and you will choose a light that fits the job instead of the biggest number on the box.
For more pocket gear, browse our everyday carry hub.
