Nephelometric methods are also employed to measure turbidity. In this method, light is allowed to strike a suspension at right angles to the eye of the observer or photoelectric cell of the instrument. The light reflected by the dispersed particles (Tyndall effect) is recorded. When this principle is employed, very low turbidities can be determined water, and this is one of the major advantages of nephelometry. Bacteriologists often use nephelometry in following bacterial growth rates.