This image was taken during the lab component of an Undergraduate course in optics. My lab partner and I are measuring the attenuation, or loss of light to absorption and leakage, in a half-kilometer spool of commercial optical fiber used for communications. A Helium-Neon laser, focused down to a point with a 10x objective lens borrowed from a student microscope, provides illumination. A photometer measures how much light reaches the other end of the fiber. The method used to 'fill' the fiber with light is very important; poor alignment can result in excessive loss of light. Here, the laser is deliberately misaligned, causing the whole cable to glow bright red.