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• The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.
• Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway leads to a type of reflection known as diffuse reflection.
• The larger the index, the slower the speed of light
• Wavefronts slow down upon entering medium of higher index of refraction
• Light twists inward when entering medium of higher index of refraction
• Ibn Sahl was an Arabian Mathematician and optics engineer associated with the court of Baghdad. In 984 he wrote a treatise On Burning Mirrors and Lenses in which he set out his understanding of how curved mirrors and lenses bend and focus light. Ibn Sahl is credited with discovering the law of refraction, usually called Snell's law.  In 1621, Willebrord Snellius (Snel) derived a mathematically equivalent form, that remained unpublished during his lifetime.
• Snell discovered that the ratio between the sine of the incident and refracted angles is equal to the ratio of the incident and refracted velocities.
• Because the velocity of light is extremely difficult to measure, it is more practical to use the indices of refraction. Due to the fact that the velocity is inversely proportional to the index of refraction, you get…
• Spear-fishing is made more difficult by the bending of light. To spear the fish in the figure, one must aim at a spot in front of the fish
• Light exits into medium (air) of lower index of refraction, and turns left.
• The sun actually falls below below the horizon, i.e., it "sets", a few seconds before we see it set.
• Entering and exiting rays are displaced from each other, but parallel.
• All rays reflect internally, but the top three rays reflect only a small percentage internally; most energy leaves the prism. The fourth and fifth rays are reflected 100 % internally.
• An incident angle at which the refracted angle is 90o Note: This can only happen in a case when light travels from a higher index of refraction to one with a lower index of refraction.
• Light within the 48.8 degree cone is detected by fish, while nothing in the air outside that cone can be seen. The only light reaching the fish outside the cone is that light (not shown) which is reflected off the bottom of the pool.
• When incident light is at an angle greater than the critical angle, the light will reflect instead of refract. When there is total internal reflection, the light will obey the law of reflection.
• Note that the shorter wavelengths of light are bent more than the longer; blue more than red.