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    • 280 – 320 nm: UV-B (harmful)
    • 320 – 400 nm: UV-A
    • 400 – 700 nm: PAR – Photosynthetically  Active Radiation
    • > 700 nm: IR (Infrared Radiation)

    • Units of light (irradiance):
      • Photon flux: mmol photons m-2 s-1 = mE m-2 s-1 (Einstein)
      • Energy: W m-2
    • Maximum surface irradiation is typically less than 2000 mE m-2 s-1 on bright day
    • Blue light contains more energy per photon than red light; therefore units of Watt and Einstein cannot easily be converted into each other. For conversion, average energy content of 550 nm light (green) is used.

    Light attenuation in sea water

    • Light decreases exponentially with depth
    • Blue light penetrates deepest into the ocean, red light is absorbed fastest (Consequences: Live seems more ‘colorless’ with depth)
    • Optical classes of water (Jerlov):
      • Coastal oceans: stronger light absorption, brownish to greenish due to shift in spectral absorbance
      • Open oceans: clearest water, deep euphotic zone, blue color

    Horizontal distribution of zooplankton

    • Light penetrates only down to 100-200 m depth
    • Herbivores, which feed on phytoplankton, are restricted to the euphotic zone
    • Carnivores, which feed on zooplankton, thrive in mid-waters
    • Omnivores, which eat both living prey and dead material (fecal pellets, dead organisms) thrive in the deep-sea