Optical crop sensor can be used to evaluate crop conditions during the growing season by directing light waves at crop leaves, and measuring the type and amount of light reflected back to the sensor. Green plants absorb much of the visible light wavelengths, particularly the blue and red light waves, and reflect much of the green light waves. Plants absorb much less near-infrared (NIR) light than red light. Darker green leaves reflect more NIR light and absorb more red light than lighter green leaves. These reflectance characteristics of plants are used to develop vegetative indices to compare the relative health of crops.