In this video, the host dicks around with a 32k lumen flashlight. Further research reveals that consumer models that put out 60k lumens are available, for the right price.
I’m wondering if one of those could be seen by an aircraft flying overhead at, say, 32k feet. I can see airplane signal lights from the ground, 32k (or more) feet below them, but how does their brightness compare to that of the flashlight? From what I could get from my limited Google Fu, it seems that aircraft use 650-watt LED bulbs; how that translates into lumens, I couldn’t say.
Anyone have any thoughts on this?
Can you see house lights and car headlights from a plane? (I’ve never flown at night)
Those have to be less than 60k lumins.
I don’t see why not, 32000’ is only about 6 miles. Street lamps are clearly visible, how many lumens are they?
Forgot to post the video in the OP. Sorry.
It’s unclear which aircraft lights you’re referring to, but the luminous efficacy of current LEDs is somewhere between 100-150 lumens per watt. It’s likely that aircraft LEDs are at the low end[sup]1[/sup] of that efficiency range, so a 650-watt aircraft LED is probably putting out 6000 lumens or so–maybe 7000 at the top end.
But Mr. Pearse’s post answers your question, doesn’t it? Low-pressure sodium street lights typically put out about 7000 lumens, though some put out much more. And what you’re seeing is mostly those 7000 lumens reflected off of low-to-middling albedo materials such as asphalt and concrete. If you can see street lights from a plane at altitude at night (and you can), you can certainly see a flashlight, even a non-fancy one.
[sup]1[/sup] Aircraft parts tend to be really expensive because of the costs of certification. That means that no one wants to pay to get new versions of components re-certified, so LEDs in use now were probably certified a while ago. That’s why I’m supposing that they’re not at the leading edge of the lumens/watt curve. (Certification costs are also why in-flight entertainment systems are so far behind even middling consumer electronics).
Just to nitpick a little, lumens (at least by itself) isn’t a particularly relevant figure when you want to figure out how far away something can be seen.
Lumens just represents the overall output of light, not how focused/intense it is. A 10k Lumen lamp that shines uniformly in all directions is not going to reach anywhere near as far as a 1k Lumen laser.
You can see a single candle from 50 miles away, if the rest of the environment is sufficiently dark.
1 candlepower = 12.57 lumens
12.57 lumens = 10**17 “green” photons/sec being emitted from the candle
50 miles = 80.4 km radius
Surface area of that sphere = 20,300 km^2 = 2.03x10^14 cm^2
So 10^17 photons/sec / (2.03x10^14 cm^2) = 10^3 photons/(sec*cm^2)
Eye pupil ~ 1 cm^2
So 1,000 photons/sec still hit the pupil/retina.
Rod/cone density of the retina = 180,000 mm^2
Such that the eye is absolutely not the limiting factor here- it is simply getting at least 1 photon in through the pupil.
I looked into the % absorbance and signal transmittance of rhodopsin as well as how many optical receptors need be triggered before the brain recognizes “light!”, but can’t find any definitive papers; however, Looking at the absorption profile, it at least absorbs very well.
So the math checks out, and if anything, Chronos could have said 1500 miles (50miles * sq.root of 1000) and been closer to the theoretical limit of candle vision!