Yes, a red light pen (visual fault locator) can be used to illuminate fibers in a tray, provided the fibers are compatible with visible red light and the pen is properly connected.

How Red Light Pens Work

Red light pens, also known as pen-style visual fault locators (VFLs), emit a 650 nm red laser that can be coupled into optical fibers to visually trace the fiber path, locate breaks, bends, or faulty connectors, and check continuity . They are designed for both singlemode and multimode fibers, typically with yellow or orange jackets, which allow visible light to pass through . Black, gray, or opaque jackets may block the light, making the pen ineffective for those fibers .

Practical Use in Fiber Optic Trays

• Connection: The pen must be connected to the fiber via a compatible interface (e.g., FC/PC, FC/APC, SC, or LC with adapters) to inject light into the fiber .
• Illumination: Once connected, the red light will travel through the fiber, and any breaks, sharp bends, or macrobending losses will appear as a visible red glow along the fiber, making it easier to identify issues in a tray .
• Range: The effective range is typically up to 3–5 km, but in a tray with short patch cords, the light is easily visible .
• Safety: These pens are low-power and safe for eye exposure when used correctly, but direct eye contact with the laser should still be avoided .

Tips for Effective Use

• Clean the fiber connector before use to avoid dust or oil interference .
• Use adapters if the tray contains LC or other small-form-factor connectors .
• Avoid high-temperature environments to maintain the pen's lifespan .
• Insert and remove connectors carefully to prevent fiber damage . In summary, a red light pen is a practical and effective tool for illuminating fibers in a tray, identifying faults, and performing continuity checks, as long as the fibers are compatible with visible red light and proper connection procedures are followed .