Davis Instruments RailLight Mini Light Fully marinzed for use in salt or fresh water Fastsolar technology quickly charges internal battery Automatic on-off light sensor On-off waterproof switch built-in Fits round rails from .65 to 1.25 inches in diameter (17-32 mm) Waterproof marine-grade solar/LED light Fast Solar charging system optimized for all outdoor conditions Provides over 8 hours of light on a full charge