![]() ![]() Photosynthetically active radiation (PAR) measured as photosynthetic photon flux density (PPFD) is the measure when dealing with light intensity for both terrestrial and underwater plants. A typical spectral diagram of an LED grow light taken with a spectrometer. In order to evaluate spectral distribution of light, it is therefore necessary to use a spectrometer as a quantum meter will only yield one absolute number in the end. Whereas a quantum sensor is adding up all of the light that passes through its optical filter independent of the specific wavelength, a spectrometer is able to identify and measure individual wavelengths. SpectrometersĪnother way of measuring PAR is by using a spectrometer or a spectroradiometer to be precise. Using this measurement procedure allows for lower cost measurement equipment than what would otherwise be possible – even though this still means that a proper quantum PAR sensor will cost a few hundred dollars upwards. In the case of a quantum PAR sensor this means the integration of photons that hit the sensor's photo diode within a specific time frame. In simple terms, a quantum sensor is a type of measurement device that works by the integration of energy. A comparison of the photosynthetic spectral response and the human eye response. Thus, quantum sensors utilize specifically tuned optical filters that only allow light with a wavelength between 400nm and 700nm to pass through. Spectral ResponseĪs already mentioned, the spectral response that matches plant photosynthesis is crucial for a PAR meter. This is why the measure you will come across is photosynthetic photon flux density (PPFD) measured in µmol/m²/s. ![]() PAR meters typically measure photon flux as the number of photons per square meter per second. ![]()
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