Illuminance (illuminance for short): It is the surface density of luminous flux on the light-receiving surface,that is, the luminous flux per unit area. Therefore, illuminanceis a quantity that indicates the degree to which the light-receiving surface is illuminated, and its unit is Lux. HOPOOCOLOR uses a handheld spectrometer to detect optical parameters such as color temperature, illuminance, and spectral wavelength. Quantum meter or PAR meter (Photosynthetically Active Radiation) is a professional photometric meter. The PAR meter will more accurately measure the light required by plants that rely on photosynthesis. PAR meters can measure photons of light, which are responsible for promoting photosynthesis. McCree pointed out in 1972 that the number of photons expressed is a better way to measure photosynthetic efficiency than the photometer measurement value Lux or Lumen. The photons received in the wavelength spectrum range of 400 to 700nm per unit area are called photosynthetic photon density PAR PPFD (Photosynthetic Photon Flux Density), and the unit is μmol/m2/s or μE/m2/s.