Is it normal for the entire fiber optic cable to glow red when illuminated

Yes, it can be normal for a fiber optic cable to glow red along its length when illuminated, especially when using a visual fault locator.When a fiber optic cable is illuminated with a red light, such as from a Visual Fault Locator (VFL), the light travels through the fiber and can sometimes be visible along the entire length of the cable, particularly if the cable jacket is translucent or the fiber is multimode . This red glow is caused by light scattering through the fiber and its protective layers, and it does not necessarily indicate a fault.Normal BehaviorVisual Fault Locators emit a bright red light (around 650 nm) that can shine through the fiber jacket, making the cable appear to glow .The glow is more noticeable in shorter cables or cables with clear or lightly colored jackets.Seeing red light at the other end of the fiber confirms that the fiber is continuous and not broken .When to Be ConcernedIf the red light is only visible at certain points along the cable, such as bends, breaks, or damaged connectors, this may indicate a fault .If the entire ferrule or connector glows excessively, it could suggest a bad connector rather than a problem with the fiber itself .A fiber that does not transmit light to the far end is likely broken and needs replacement .SummaryA red glow along the entire fiber is generally normal and expected when using a VFL or similar testing device. It indicates that light is traveling through the fiber, and the cable is intact. Only localized bright spots, absence of light at the far end, or unusual connector glow should raise concerns about potential faults .