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1) photometer or common light meter (cheapest) - measures amount of luminance
    Expressed as:
    a) foot-candle (ft-c) - 1 lumen per square foot

    b) lux - 1 lumen per square meter 

        1 foot-candle = 10.76 lux

2) quantum sensor - measures actual light intensity or light energy in the 400-700 nm 
                                      wavelength band.
    photosynthetically active radiation (PAR) - light intensity in the 400-700 nm
                                            wavelength band that is used by plants in photosynthesis.

    Expressed as
    a) microEinstein per second per square meter - mEs-1m-2 (400-700 nm)

    b) watts per square meter - Wm-2(400-700 nm)

Color Sensitivity of a Photometer vs. a Quantum Sensor



3) radiometer - measures radiant energy received at all wavelengths, i.e. total solar radiation.

4) spectral radiometer - measures the intensity at each wavelength (i.e. color spectrum
from a light).