Reflections Occur in Transparent Window as well(유리창에서 일어나는 빛의 반사)

When you look out of your window at night, you'll see yourself's reflected image, just as if you were standing in front of a mirror. Why does this happen? And why doesn't it happen during daytime? This is due to the reflection occurring in the window. My guess, before doing some researches about the topic, was that a transparent window also has some features of a mirror, and that the reason the reflection cannot be see sometimes is somewhat related to the power of the reflected light.

 

http://khayyam.kaplinski.com/2011/10/reflective-water-with-glsl-part-ii.html

Reflection always occur at the border of two different medium, and when the medium are transparent, refraction also happens. In our case, which the medium are air and glass, both of the events will happen.when reflection and refraction happen, the incident light and the reflecting light have the same angles from a line(N) that is perpendicular to the 'mirror' and is in the center of the two light. Also, the equation

is satisfied. The percentage of power of the light reflected can be shown as the reflection coefficient R, which can be dervied from Fresnel's Equations. Fresnel's Equations are:

When light travels into a medium with an angle perpendicular to the border, the reflection coefficient R is: 

When the first medium is air and the second medium is glass, the reflection coefficient can be calculated as 0.04, which means 4% of the light is reflected,. Since there are two borders of medium in the case of a window, the total reflected light is 4+0.04*96=7.84% of the original light.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/imgpho/refco2.png

Conclusion: The reason we see ourselves reflected in a transparent glass at night but not day is that the window, or glass, does reflect light but in a such small amount that it cannot be seen when there is daylight outside.