VIVID Ultimate Flashing Safety Collar-Blue Size Large Illuminated with Rechargeable Battery Large Collar (18-22" long and 1 3/4" W) Correct Collar Size: The sizes listed above indicate the maximum size with the buckle fastened. Measure your pet's neck before ordering. You may wish to add 1" - 2" to the measurement for your dog's comfort. Rechargeable battery Glow in the dark reflective strips Light sensitive setting that automatically switches collar on in the dark