If you buy your LEDs based only on Lumens, you may be missing the point that Lumens don’t equate to actual situational effectiveness–a.k.a. Candela is likely the most mission-critical measurement when choosing lights for your aircraft because its entire purpose serves to communicate how far you’ll be able to see downrange on takeoff and landing, and how far away other aircraft can be in order to see you in the sky before it’s too late. Pilots will have a much easier time spotting airplanes decorated with high-Candela anti-collision lights while the sun is still up. It’s also important to note higher Candela measurements mean the light source is more situationally effective during daylight hours. It would have low Lumen rating because it’s not great at dispersing light to the immediate area around the light source, but it would have an exceptionally high Candela measurement since it focuses in a single direction–and Batman can see its light from great distances. By definition, Candela (also known as “candlepower”) is “the base unit of luminous intensity in the International System of Units that is equal to the luminous intensity in a given direction of a source which emits monochromatic radiation of frequency 540 × 1012 hertz and has a radiant intensity in that direction of ¹/₆₈₃ watt per unit solid angle.” Candela tells us how far away we can be from a light source while still being able to see it. The kicker? Both of these landing lights could have the same number of Lumens.Ĭandela places an emphasis on visibility from a distance while factoring in the total volume of light within a certain beam angle and direction. Landing light B would allow the pilot to see further down the runway and possibly avoid a deer strike. If these lights were on airplanes landing on parallel runways at night at the same time and position in glide slope, landing light B would be able to light up the runway well before landing light A. Landing light B has a high lux measurement. For example, landing light A has a low lux measurement. Lux factors in the assembly’s efficiency at distributing light to a specified area–in this case, the runway. A landing light might have an insanely high Lumen count, but that doesn’t mean it will have high Lux levels. The Lumen measurement does not change, of course. As you descend and get closer to the runway, the runway gets brighter, and your landing light’s lux reading increases. Imagine your final approach to the runway at night. By definition, Lux is “a unit of illumination equal to the direct illumination on a surface that is everywhere one meter from a uniform point source of one candle intensity or equal to one lumen per square meter.” The closer the surface to the light source, the higher the lux reading.

Lux tells us how much light actually falls on a surface from a given distance. This issue is why we prefer to highlight (no pun intended) Lux and Candela. As a result, Lumens do not tell you the actual, real-world effective output of the light assembly–especially when factoring in the assembly’s electrical efficiency, lens clarity, distance from the runway, presence or absence of daylight, and so on. Lumens refer to the potential amount of light emitted from the source area in an ideal world, based on each individual LED chip's rating multiplied by the total number of LED chips in the light assembly. The issue with selecting an LED based only on its Lumen count is that the measurement only paints a theoretical picture of the LED’s performance. Lumens are “a unit of luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one candle intensity.” Lumens tell us how much light a light source should emit in the immediate area around it. LIGHTS WITH THE MOST LUMENS ARE THE BEST, RIGHT?

Candela lighting system