During the day, these energy-efficient solar lights harness sunlight energy to charge their internal Lithium Battery. At night they automatically turn on, emitting a bright glow for your fence post line. Solar fence post lights add ambience to any outdoor setting including decks, patios, and swimming pools. DURABLE CONSTRUCTION - Heavy duty ABS plastic casing is durable, designed to withstand the elements. ENERGY EFFICIENT LED - Improved 1 Bright LED provides brighter glow for better visibility. 100% SOLAR POWERED - Top mounted solar panel charges the AA 600mAh Ni-mh battery, for an energy efficient lighting solution that requires no external wiring. LA STS FOR 8 - 10 HOURS - Once fully charged, these lights will provide 8 to 10 hours of illumination, for an evening full of ambiance. Product Dimensions - 5.75" x 5.75" x 4.5", Base Dimensions: 4" x 4" Post Size Fitting; these post caps will ONLY fit on 4" x 4" Vinyl, PVC or Plastic posts. The opening on the bottom of the post cap which fits over the top of the post is exactly 4 1/16" x 4 1/16". *** This post cap is not designed for use on Wooden posts!