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Source: https://i.ytimg.com/vi/hNgu1vypV3g/hqdefault.jpg

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Why is the white Landing light more visible on a fine sunny day and not the other two? I would have assumed the Red one to be most visible during flight, followed by Green but from a distance on a sunny day you can only see the white Landing LED very clearly but neither of the other two. Could it simply be because of the intensity of white light being more (having 2 bulbs) as compared to the other two having 1 bulb each?

This picture does illustrate the position of lights but since it was taken in a dark setting it doesn't do justice to how it appears during the day. Those red and green lights are not visible at all from any distance beyond a few meters.

When its a little dark (evening / cloudy) they are clearly visible.

Please Note: It is not really so that I expect to see all these 3 lights clearly on a bright day, obviously against sun light they stand no chance. I am just curious as to why the colored ones are far less visible than the white one.

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    $\begingroup$ sort of related: You dont use nav lights that often during daylight. $\endgroup$ – Jamiec Aug 25 '16 at 7:28
  • $\begingroup$ Was this pictures really taken in broad daylight? It looks more like dawn or dusk to me. Plus: It's a model. The representation of real aircraft lighting is not given, as the lights are only scaled in size. On a real Cessna, they wouldnt be so visible in daylight, not even the landing light. $\endgroup$ – SentryRaven Aug 25 '16 at 9:10
  • $\begingroup$ Yes this picture is not a daylight one, I chose it just to present the lights themselves $\endgroup$ – Hanky Panky Aug 25 '16 at 9:11
  • $\begingroup$ Was the traffic coming at you, aka opposing traffic? $\endgroup$ – SentryRaven Aug 25 '16 at 9:15
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    $\begingroup$ Same situation as with your car headlights high beams being much more visible than indicators, even though indicators are meant to be a visible signal, not high beams. $\endgroup$ – Agent_L Aug 25 '16 at 11:45
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Navigation or Position Lights are meant to be used at night-time and can be used when precipitation or weather in general deteriorates to the point where the lights will help you identify an aircraft's position, distance and orientation of the aircraft. During daylight operation, the use of navigation lights is not required as you can identify the shape of an aircraft against the horizon or background.

Navigation lights are also installed at the sides of the aircraft, spanning a range of 110° measured from the extended centerline of the aircraft to each side.

The landing light however is pointed directly along that extended centerline, which makes it easier to spot if the aircraft is approaching you. It also is of higher intensity than the navigation lights, as it needs to give a pointed illumination for a larger area in front of the aircraft, rather than giving a steady and 110° wide illumination.

Position Lights on Aircraft

(Image Source: Wikipedia - Author: Trex2001 Clem Tillier)

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The navigation lights are meant to give away the airplane's orientation (i.e. which direction it is travelling) at night. The red and green lights are small. Their purpose is to be observable from a long distance, which only requires a small light. For the same reason, the anti-collision red lights of tall structures are small as well.

The landing lights (white light) are meant to illuminate the runway, taxiway or any terrain in front of the aircraft. The light must travel to a certain distance in front of the aircraft then bounce back. They are very bright. To experience that, go to a busy airport at night and stand near the approach end of a runway. In fact, standing next to an airliner with its landing lights fully on would likely damage your eyes.

Landing lights must also be turned on when any aircraft enters an active runway. Here they serve the same purpose of turning on the headlights of your car at night: to make sure others can see you. This regulation came after an airliner landed on an occupied runway at night. It was determined that the plane on the ground blended in with the runway lights, and the pilots of the landing aircraft were unable to spot it. Had the plane turned on its landing lights, the very bright light source would have give away their position and alerted the crew to abort its landing.

The model is simply a replica of the real life scenario.

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  • $\begingroup$ Their purpose is to be observable from a long distance, which only requires a small light; But that's exactly what they aren't doing $\endgroup$ – Hanky Panky Aug 25 '16 at 7:58
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    $\begingroup$ And knowing the orientation of an aircraft is an extremely important factor in model aviation as well. Not that without the lights its impossible to tell but was just curious and disappointed that they didn't do their job well but i guess on a model they are mostly for cosmetic reasons because night time model flight is a challenge in itself with or without those. +1 $\endgroup$ – Hanky Panky Aug 25 '16 at 8:23
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    $\begingroup$ @HankyPanky During the day you don't need the lights because you can see the aircraft. $\endgroup$ – Stop Harming Monica Aug 25 '16 at 10:58
  • $\begingroup$ Downvote for misinformation about supposed landing light use requirements. There is a difference between an operable equipment requirement and use recommendations. Company SOP is another variable. $\endgroup$ – J Walters Aug 25 '16 at 13:23
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The OP asks why the white "landing light" is more readily visible during the day than the red or green nav lights.

The primary reason for the white light being more recognizable in this instance is that it is providing more photons than the green or red lights. The landing or taxi lights consume more power and produce more light than the nav lights.

In general, the eye sensitivity is a function of the photons received, adjusted for the sensitivity of the eye for the color(s) received, and adjusted for contrast (brightness gradient). The peak photoresponsivity of the human eye is about 560 nm, which is a green-blue color and shifts to 507 nm at night, which is more blue. The white light of the landing light is comprised of most or all colors which the eye is sensitive to, normally considered colors with wavelengths ranging from 400nm (violet) to 700nm (red), where nm is the wavelength of the light, nanometers, not nautical miles.

But to be clear, the visibility is a function of amount of radiation emitted, adjusted for the sensitivity of the eye, and in the OP case, the answer is simply that the landing lights have a much higher level of emissions than the nav lights.

As a tangentially relevant aside, the human eye, when night accommodated, has a very high quantum efficiency. Quantum efficiency is the ability to convert a photon (the smallest unit or packet of light) into a neural response which is recognized by the brain. Once impressed by the ability to observe lit cigarettes from 5000 ft and higher altitudes while doing surveillance work, I later investigated the responsiveness of the human eye. In general, a younger eye can reliably detect single photons. Things like available nutrients affect that, those nutrients including oxygen. Lay on the ground on a moonless night, and look at the stars, and then take a breath or two of oxygen, and suddenly there will be many more stars.

To summarize, the reason the white light cited by the OP is more visible is that it is giving off more photons which are detectable to the observer.

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  • $\begingroup$ Great answer. This is more of what i was originally looking for $\endgroup$ – Hanky Panky May 14 '17 at 3:06

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