<p><b><i>HOW IT WORKS:</i></b></p> <p> </p> <ul> <li> The exact reason that these pebbles can give off light in darkness is that they can absorb and store light, either natural or artificial, especially visible light of wavelength under 450 NM.</li> <li> When in darkness, these pebbles give off light that is visible and fairly bright during the first 2-3 hours. Then they became less and less bright as there is no light around for them to absorb. The dim afterglow can last 8-10 hours.</li> <li> How much the glow is visible at some degree depends on how dark the surrounding is, the darker the more glow can be seen.</li> <li> When there is visible light around, these pebbles begin another circle of absorbing-giving off light .</li> <li> Actually these pebbles give off light at the daytime too, but only far less visible as in darkness.</li> <li> So, when you first receive these pebbles, they might not glow in darkness, because they might have given off all light they absorbed in dark package box. Put them under light sources for 5-10 minutes, they glow in complete darkness again.</li> <li> In theory, these self-luminous pebbles can function for up to 15 years. </li> </ul> <p><b><i><br></i></b></p> <p><b><i>Warm tips:</i></b></p> <ul> <li> The darker the surrounding and the more exposure to visible light, the more bright glow can be seen.</li> <li> When applying these glow pebbles, do not stack them on top of each other but spread them out flat for full exposure to light.</li> <li>  Keep away from children for chocking hazard.</li> </ul> <p><br></p> <p><b><i>SPECIFICATIONS</i></b></p> <ul> <li>  <b>Materials:</b> long-afterglow luminous powder, polystyrene resin, which are non-toxic and do not contain any radioactive elements.</li> <li><b> Size of one piece of stone: </b>Approximately 0.6"-1.1"</li> </ul>