Measurement using light, for example, spectroscopy, is rapid, low cost and easy for maintenance of the instrument, and used for diagnosis of agricultural crops. Visible-near infrared method has been used non-destructively measuring color of leaf and near infrared method measuring fruit quality for practical use, respectively. On the other hand, infrared spectrophotometers have also evolved fourier transformation type. Therefore, ultraviolet, visible, near-infrared and infrared spectroscopy method is mainly described. Moreover, nitrate ions determination using light was also focused for mainly vegetables.
