Action spectrum

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The action spectrum is the spectrum of light which correlates to biological activity. For example, in 1881, Thomas W.. Engelmann learned that the green algae spirogyra undergoes photosynthesis most effectively when exposed to red and blue light.^[1] Melatonin suppression, a physiological activity involved in the regulation of the pineal gland, is another example of an action spectrum. Light suppression of melatonin secretion takes place at specific wavelengths.^[2]

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