sentences:  The charts "Understanding wavelengths in fiber optics" and "Optical power loss (attenuation) in fiber" illustrate the relationship of visible light to the infrared frequencies used, and show the absorption water bands between 850, 1300 and 1550 nm.The infrared light used in telecommunications cannot be seen, so there is a potential laser safety hazard to technicians.The eye's natural defense against sudden exposure to bright light is the blink reflex, which is not triggered by infrared sources.