Kitchen Panda
Enlightened
So I was wondering how far a flashlight beam could be seen in good conditions. The ANSI FL1 standard rates working distance to 0.25 lux, the illumination produced by the full moon.
Astronomers have been measuring brightness of objects for centuries, so it's not hard to find a table showing the moon has "magnitude" -12.5 (1 lux corresponds to magnitude -14, and 5 magnitude steps correspond to a 100-fold change in illumination; the dimmest stars visible by someone with excellent vision and really dark sky is magnitude +6).
Also according to the table, the brightest stars in the night sky are magnitude 0. So, that's 12.5 magnitude steps, cranking the algebra, that means you can easily see an object that is providing 99,000 times less light than the full moon. The illumination drops off as the square of the distance and the square root of 99,000 is 315, nearly.
So, all this rigamarole says that if you take the ANSI FL1 working distance and multiply it by 315, you'll have a range at which the light will appear about as bright as the brightest stars.
According to that, the TK70 should be visible up to 130 miles! There's probably some additional atmospheric factors that crop up over such great distances, but it's kind of cool to imagine this. That doesn't quite reach the International Space Station.
Bill
( But if I'm forced down somewhere in Northern Ontario at night, you can bet if I can see *your* lights, I'll be flashing all of mine in your direction!)
Astronomers have been measuring brightness of objects for centuries, so it's not hard to find a table showing the moon has "magnitude" -12.5 (1 lux corresponds to magnitude -14, and 5 magnitude steps correspond to a 100-fold change in illumination; the dimmest stars visible by someone with excellent vision and really dark sky is magnitude +6).
Also according to the table, the brightest stars in the night sky are magnitude 0. So, that's 12.5 magnitude steps, cranking the algebra, that means you can easily see an object that is providing 99,000 times less light than the full moon. The illumination drops off as the square of the distance and the square root of 99,000 is 315, nearly.
So, all this rigamarole says that if you take the ANSI FL1 working distance and multiply it by 315, you'll have a range at which the light will appear about as bright as the brightest stars.
According to that, the TK70 should be visible up to 130 miles! There's probably some additional atmospheric factors that crop up over such great distances, but it's kind of cool to imagine this. That doesn't quite reach the International Space Station.
Bill
( But if I'm forced down somewhere in Northern Ontario at night, you can bet if I can see *your* lights, I'll be flashing all of mine in your direction!)