When lighted, V-shaped LED lamp tubes with white PC covers show a faint black line at the center directly below the lamp tube. Not a product defect. The lamp's optical and structural design and light propagation path and physical obstruction cause this behavior.
Structure-based physical shielding
These lamp tubes place LED light beads tightly on a narrow PCB board at the bottom valley of the V-shaped construction. The V-shaped hole will be covered with a white PC cover for optical distribution and light source fixation. Thus, the PCB board and its supporting structure on both sides prevent some direct light from below. The black line is formed by this component's shadow at the light path's center.
Milky white diffuser diffusion limit
A point light source becomes a uniform surface light source when the milky white PC diffuser continually reflects and diffuses light via its interior particles. Diffusion has a physical limit. The shadow intensity is high for a long strip-shaped barrier just above the light diffuser and parallel to the observer's line of sight. A black line forms when the environmental background brightens and this linear area at the visual center is not adequately lighted.
Angle and space contrast
This black line's prominence depends on observing angle. The black line is most visible when the human eye is exactly below the lamp tube and perpendicular to its long axis. The shading effect is greatest when the line of sight is parallel to the shading item at the bottom of the V-shaped structure. If you move from this optimal viewing angle, the black line will blur. Open spaces with consistent ceiling backgrounds increase visual contrast, making this black line easier to see.
Understanding this phenomenon reveals that it is a physical imaging outcome of a unique optical design, not a failure.
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