The two most common illumination measurements you’ll see when comparing flashlights are lumens and candela. While on the surface they might sound like they’re referring to the same thing, they aren’t. They are somewhat related, but it’s important to understand the distinction.
Lumens
Lumens are the total light output. Think of it as a measurement of brightness. A flashlight rated at 1,000 lumens will be twice as bright as a 500-lumen one. However, and this is the important part, the lumen rating doesn’t take into account the beam size, shape, or pattern. It is strictly a measurement of overall illumination, nothing more. This is called luminous flux.
Candela
Candela is Latin for candle. For many years, this was the standard measurement for lights. It was sometimes called candles or candlepower. The idea was that one candela was equal to the brightness of one standard candle of a specific size and composition. Today, we use candela to measure the light output in one specific direction.
Think of what you see when you power on a flashlight. Typically, there is a small area at the center of the beam that’s the brightest, right? That’s what candela is measuring, the brightness of that small area, what we call the luminous intensity. Candela will also be an indication for throw, or how far the beam of light will travel. Higher candela means longer range.
Understanding the Difference
Here’s one way to understand the difference between lumens and candela. The lamp in your living room, the one that lights up most of the room, has a good lumen rating, but a relatively poor candela rating. It provides a fair amount of light, but it’s widely dispersed. On the other hand, a flashlight with a focused beam might not have a lot of lumens, but the candela rating will be relatively higher.
Real World Applications
So, what does all this translate to when shopping for flashlights? For starters, remember that the lumens rating doesn’t tell the whole story. Sure, a 500-lumen light is going to be pretty bright. But it might not be suitable for your specific needs.
For example, let’s say you want a light that you can shine into the backyard if you hear an odd noise. You probably want something that’s more focused, so you can see specific areas well, rather than providing unfocused light to a larger area. In this case, candela is as important as lumens.
On the other hand, if you’re looking for a pocket flashlight that you can use for lighting up dark hallways during a power outage or for seeing what you’re doing when jump-starting the neighbor’s car late at night, then candela isn’t as much of a factor.
Limiting Factors
Just as you need to understand the difference between lumens and candela, you should recognize that all of the posted ratings for a given light are for perfect conditions. Outside the testing facility, there are going to be limiting factors in play. These could include a dirty lens, fog, precipitation, even dust floating in the air. Any of these will disrupt your light and reduce its effectiveness.
