What makes light "glow"? Hi, First post from a newbie... so forgive the naivety... Light is described as an electromagnetic wave/particle... but what actually gives light its "brightness", allowing it to illuminate the surroundings through which it travels? Also, another question if i may... I know that the speed of light, 186,000 miles per second, refers to light speed in a vacuum, however is the speed of light on earth (through air that is) much different? How much slower is it? Thanks in advance for all your help.