Spectra of sunlight and artificial light sources.

<p>For light dependent processes the photon flux has a higher relevance than the irradiance since photoreceptors are activated by photons, thus we compared spectra plotted in μmol/m²/s photons versus the wavelength. (A) Spectrum of sunlight on a cloudless summer day in Vienna at 12:00 hours in grey (22437 μmol/m²/s photons) and at 19:00 hours during sunset in orange (1268 μmol/m²/s photons). (B) Spectrum of a Philips compact fluorescent lamp (14W, 5.1 μmol/m²/s photons). Red arrowheads indicate gaps in the spectrum. (C) Spectrum of an Osram incandescent lamp (15W, 5.8 μmol/m²/s photons). (D) Spectra of a Winger white daylight LED (1W, 6500K, 1.4 μmol/m²/s photons) in grey, and warm white LED (1W, 3200K, 1.1 μmol/m²/s photons) in orange. The main difference between a daylight and a warm white LED is the light intensity around 450 nm. Note the similarity of these light sources to respectively daylight and twilight in A. All measurements except for sunlight were performed at a distance of 60 cm from the light source, which corresponds to the distance between light source and sample in our experimental instrument.