Gardner Tritium-Max Green Betalights are 6mm x 2mm light sources designed for use with ATTs Alarms. They provide a continuous light output, with the tritium gas mixture sealed into the glass tube under maximum pressure to deliver the highest possible brightness available from this type of isotope. Brightness in any betalight depends on two factors: the colour of the light emitted and the total volume and pressure of the gas trapped inside the glass tubule. A lower volume of gas at maximum pressure will never be as bright as a larger volume at the same maximum pressure. Each colour is created by blending different phosphorous compounds into the tritium gas, so light output varies between colours, with green always being the brightest. - 2 per pack