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During long times of the cruise flight, is the internal light normally switched on or off inside the cockpit?

Knowing it is generally dark in the night would make a smartphone-based night time logger easy to write.

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    $\begingroup$ Sounds like an XY problem to me. ;) $\endgroup$ – bogl Jul 6 at 8:18
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    $\begingroup$ Why would a pilot need a smartphone to tell them when it is nighttime, or dark? It sounds like you're trying to solve a problem that doesn't exist. Aircraft already have extensive data logs. $\endgroup$ – J... Jul 6 at 19:21
  • $\begingroup$ Related (maybe the motivation for this question?): aviation.stackexchange.com/questions/79191/… $\endgroup$ – user3067860 Jul 6 at 19:45
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    $\begingroup$ What information is to be logged, exactly? $\endgroup$ – Peter Mortensen Jul 6 at 20:40
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    $\begingroup$ If sunset happens in the middle of the flight, I assume, only time after sunset should be logged as a night time. By sensing where it happens, a phone would be able to produce the two log entries, day flight duration and night flight duration. Otherwise this cannot be done automatically without knowing the flight path, but GPS sensor of the typical consumer mobile device time to time just does not work in flight. $\endgroup$ – h22 Jul 6 at 21:15
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White lights are usually off in the cockpit in night flights to protect pilots' night vision. Red lights are sometimes used as these do not impact night vision.

One of the challenges you'll run into is knowing when it's night, as the start of night varies by latitude and the exact time. Phones generally set their time from the mobile network, which may be absent on long flights, especially those over water. A pilot flying a jet over the pacific may may have a phone that is hours off the local time.

Putting my (albeit old and tattered) mobile developer hat on I would suggest you look for ways the phone can tell you whether it thinks it is night or day and use that, plus a manual selection for day/night mode. Look at the Android UIModeManager as a way this could be done native.

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    $\begingroup$ I guess you can rely on the phone's integrated GPS to know exactly where and when you are, then deduce from there if it's time for red or white lights. $\endgroup$ – Diego Sánchez Jul 6 at 9:07
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    $\begingroup$ Sure @DiegoSánchez, with some completely doable calculations. There's probably code out there in the public domain to do it. However, you might be able to make it much easier: Q: 'Phone, is it nighttime?', A: 'Yes' $\endgroup$ – GdD Jul 6 at 9:10
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    $\begingroup$ I agree with the first paragraph for VFR flying, but I know a few long-haul airline pilots who say they do tend to keep the cockpit lights on in cruise to help stay awake, unless there is something interesting to look at. Of course they need to be off for takeoff and approach. So I think the answer really depends on what type of flying it is and which segment they are in. $\endgroup$ – Ben Jul 6 at 11:15
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    $\begingroup$ @MichaelHall My understanding is that the OP wants to prevent flashing a bright, white screen to the pilots if they fire up the application during the night. I would expect a trained pilot to be able to tell day from night, yes, but this little help would indeed be a nice touch as it would avoid killing their night vision. I wish mi car was half as smart when driving in the night. $\endgroup$ – Diego Sánchez Jul 6 at 17:33
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    $\begingroup$ @Diego Sanchez, Interesting, I didn't interpret the question that way. Read the second sentence again, I think he is asking to know if measuring the ambient light in the cockpit would be a reliable way for the app to recognize it was night. Leaving a white light on would mess a simple algorithm up. $\endgroup$ – Michael Hall Jul 6 at 20:53
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If you are asking about logging night VFR -time, you are not concerned with lighting conditions. Night time is logged according to regulation based definition of night (at least EASA), tables for night time are usually available from local aviation administration websites.

Your logger simply needs to know your position, date and time, and refer to the official table or definition of night if table is not available. EASA defines night as

" ‘Night’ means the period between the end of evening civil twilight and the beginning of morning civil twilight or such other period between sunset and sunrise as may be prescribed by the appropriate authority, as defined by the Member State."

Not quite as informative as one might like, but this is how thing work in avaition...

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    $\begingroup$ That's because EASA is not actually a civil aviation authority and the member states may be using different definitions. But civil twilight is precisely defined, and alternate is certain time after sunset/before sunrise (1 hour in the USA), which is also precisely defined. You just need to keep track of the definition by country. $\endgroup$ – Jan Hudec Jul 6 at 10:10
  • $\begingroup$ Good clarification Jan 👍🏻 $\endgroup$ – Jpe61 Jul 6 at 10:18
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    $\begingroup$ … now thinking of it again, there is one point I don't know though – does the definition of the country that issued your license, or the country where you are flying count (I would expect the former, actually). $\endgroup$ – Jan Hudec Jul 6 at 19:09
  • $\begingroup$ Oh, that's a tough one. You obviously operate under the rules of the country you fly in, but logging time... hmmm... if the country you fly in specifies it's night VFR, I would log it as such, even if my "home rules" did not consider it a night. You excercises the qualifications of your licence in accordance with the local regulations. $\endgroup$ – Jpe61 Jul 6 at 19:49
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To strictly answer the title question, at least in GA operations, we typically fly with the cockpit lights off to avoid ruining our night vision. We do sometimes use red lights to see stuff in the cockpit, though.

However...

It's unlikely that a photosensor will be very useful for determining which hours count as day vs. night. Lots of factors will affect the relationship between time of day and received light on a photosensor in the cabin. These include, but aren't limited to: position, altitude, heading, orientation of the phone, latitude, time of year, weather, etc. This is compounded even more by the fact that what counts as "night" varies, not only by country, but even within the same country depending on the purpose in question!

For example, according to this AOPA (Aircraft Owners and Pilots Association) article, the US FAA definition of 'night' for purposes of logged flight time for private or commercial certification is the one in 14 CFR 1.1:

Night means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the Air Almanac, converted to local time.

It's highly unlikely that you'll be able to figure that out with a photosensor on a phone in the cabin. You'll instead need the aircraft's location and time (and the formulas for figuring out when civil twilight starts and ends.)

However, for purposes of being 'night current' in order to be allowed to carry passengers at night, the definition of night is defined differently in 14 CFR 61.57(b):

the period beginning 1 hour after sunset and ending 1 hour before sunrise

Indeed, it turns out that the FAA uses several different definitions for different purposes, as described in detail in answers to the question How does the FAA define day and night? And that's just the U.S.

So, what you'll really need to solve your problem is:

  • Aircraft position
  • Time
  • The relevant rule for whatever purpose you're wanting to know about day vs. night.

Thankfully, the first two should be easy with a modern smartphone. At least for the U.S. definitions, local time should be irrelevant. Your phone's system time (in UTC) and position should suffice, so crossing time zone boundaries shouldn't matter.

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  • $\begingroup$ Ironic that the legalistic definitions fail to capture the one parameter that differentiates the two in any meaningful way... $\endgroup$ – Michael Hall Jul 6 at 23:01
  • $\begingroup$ @MichaelHall Are you referring to sun disc angle relative to the horizon? If so, the legal definition of "civil twilight" does encompass that, as do the definitions of "sunset" and "sunrise." Granted, I would agree that "1 hour after sunset/before sunrise" is a silly legal definition, since that can result in a dramatically different amount of lighting depending on latitude and time of year. $\endgroup$ – reirab Jul 6 at 23:32
  • $\begingroup$ No, I am referring to the "dramatically different amount of lighting" between day and night. I understand that there is some subjectivity during the transition period, therefore it needs to be defined somehow. $\endgroup$ – Michael Hall Jul 6 at 23:39
  • $\begingroup$ @MichaelHall Defining it in terms of actual lighting would be really hard to do and almost impossible to enforce. It would vary from day to day based on weather and also from one nearby location to another based on terrain (e.g. it gets dark significantly earlier at the base of the Eastern slope of a mountain than at its summit or on its Western slope.) Astronomical definitions, on the other hand, result in times that are consistent within an area and don't depend on weather (and, thus, can be computed as far in advance or retrospect as desired.) $\endgroup$ – reirab Jul 6 at 23:44
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    $\begingroup$ @MichaelHall Agreed and I do pretty much the same thing. I'm just saying that using amount of light to set the legal definition would be tough because, unless you have a photosensor on a gimble that remains aimed at the sun, it's subjective to measure and, even if you do have that, clouds, haze, mountains, etc. will mess up accuracy. "Night starts at a time when the solar disc is x degrees below the horizon and is published in the pilot's almanac" is much less subjective than "night starts when it's dark," even if pilots really use something more resembling the latter in normal practice. $\endgroup$ – reirab Jul 7 at 3:54

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