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Outdoor Spectra
PAR summation

Spectral data can be integrated over the 400 to 700 nm waveband to
compute the Photosynthetically Active Radiation (PAR) using the formula:
1/(B*h*c) * 400  700 λ * E(λ) dλ, where
    B = Avogadro's number = 6.0221413e17 photons/µmole
    h = Planck's constant = 6.62606957e-34 watt s2
    c = speed of light = 299792458e9 nm/s
    λ = Spectroradiometer wavelength (nm)
    E(λ) = Measured Spectral Irradiance at λ (W/m2/nm)