Our new Premium grade product line has been formulated and powered by CORE Glow technology to maximize the brightness and longevity of our glow rocks. Our Premium grade glow is 60% brighter than other glow stones available in the market. 3-8mm Size Premium Grade Glow Stones: Emission wavelength: 420nm Optimum excitation wavelength: 200 - 450nm (standard and UV light) Lux: 8 (0 hours), 2 (2-10 hours) Our Premium Grade is: 60% more powerful then other glow stones available in the market Glow Duration: 12+ Hours Charge time: 10 mins (UV preferred) Lifespan: 20+ years Environmental Accountability: It Glows Premium Grade Glow rocks is a highly durable product, designed for long-term usage. We are committed to continuously innovating to make our products longer-lasting, more durable, and brighter, in order to continuously improve our environmental impact. Thank you for joining us on this journey. It Glows products are compliant with Dark Sky guidelines for light pollution reduction.