if you think about the colors of the rainbow red, orange, yellow, green, blue, indigo, and violet. That list of colors shows you the spectrum of visible light and the further right (towards violet) you go the more energy the waves have while the more left (towards red) you go the less energy the waves have. wavelength and energy are inversely proportional meaning that as energy goes up, wavelength goes down. therefore the more right (towards violet) you move in the spectrum, the smaller the wavelengths get.
