# Can I see the light from 10 million km away?

If light is switched ON, only for a second, and the distance between the observer and the light source is 10 million kilometers, can I still see the light spark?

For example, let's assume that the source is the Sun and the observer is a human eye.

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Yes it can be seen, given that you do not get much noise and that your sensor is sensitive enough for it to be able to detect the signal. As you have not specified anything about the light not much can be concluded, more than that it depends on the sensor, the transmitter and the noise from everything else.

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$I=I_{0}e^{-\mu_{e} x}$ where $\mu_{e}$ is known as extinction coefficient. It is the sum of the absorbtion and scattering coefficent. $\mu_{e}=\mu_{s}+\mu_{a} = \frac{1}{l_{s}} + \frac{1}{l_{a}}$