Knowledge Bomb: Candela vs Lumens

Hey guys,

The terms Candela and Lumen get tossed around a lot during discussions about weapon lights and handheld lights. Here, we'll explain the difference. 

First, what's a Lumen?

Well, the technical definition is:

"the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 10¹² Hz, K_cd, to be 683 when expressed in the unit lm W^–1." 

Basically, a lumen is a measurement of how much light is created by a source. 

Okay, so what the hell is a Candela?

The technical definition of Candela is:

"The fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 10¹² Hz, K_cd, to be 683 when expressed in the unit lm W^–1, which is equal to cd sr W^–1, or cd sr kg^–1 m^–2 s³, where the kilogram, metre and second are defined in terms of h, c and Δν_Cs."

In non-nerd terms, Candela basically describes the intensity or brightness of the light at a given point. 

Sometimes a good analogy goes a long. When explaining lumens and candela, think of an adjustable garden hose nozzle. The overall water volume output from the nozzle is the lumens. But, when you adjust the nozzle you can redirect that same volume into a very powerful, focused stream that travels a farther distance, or a weaker, wider stream that covers more area, but has less power and doesn't go as far...this equates to candela. 

Bottom line, the higher the lumens, the brighter the light. The higher the candela, the more narrow the beam.

Here's demo:

These two lights each project 1000 lumens. The one on the left (Surefire X300U-B) has 11,000 candela, thus a wider flood pattern but a weaker and less defined hotspot than the light on the right (Streetlight TLR-1 HL) which has 20,000 candela. 

Within the context of weaponlights and handheld lights, it's common practice to choose a light that has both a flood and a defined hotspot. The flood helps illuminate your immediate surroundings, while the hotspot punches a tight and powerful beam of light within the center of the flood to illuminate a specific location. The hotspot is also good at punching through photonic barriers such as fog, smoke, or rain that render lights without significant candela, ineffective. 

A high candela light with a hotspot is also effective at directing that tight light beam into an assailant's face and negatively affect their ability to see. This is an obvious benefit. 

We carry a variety of weaponlights and handheld lights with all sorts of Lumen and Candela ratings. While no specific light is the "best" light for every situation, we hope that this information helps you make an informed decision so you can choose the best light for your particular needs. 

Stay Safe and Stay Focused

- The Musa Team