The electromagnetic spectrum is the range of types of solar radiation based on wavelength. Radio waves have longest wavelength. Higher energy wavelengths are screened out by ozone layer in upper atmosphere. Lower energy wavelengths are screened out by water vapor and CO 2 . Consequently, both the organic molecules within organisms and processes, such as vision and photosynthesis, are adapted to radiation that is most prevalent in the environment.
Photosynthetic pigments use primarily the visible light portion of the electromagnetic spectrum.
Carotinoids are yellow-orange pigments which absorb light in violet, blue, and green regions. When chlorophyll in leaves breaks down in fall, the yellow-orange pigments show through. A spectrophotometer measures the amount of light that passes through a sample of pigments. Graph of percent of light absorbed at each wavelength is the absorption spectrum. The overall equation for photosynthesis is usually stated as carbon dioxide plus water goes to carbohydrate plus oxygen.