I'd recommend some care when using a halogen light source, as they produce as much heat as light. The best lume charging I've experienced is by using an LED torch which produces no heat and so can be held close to the crystal and dial's luminous material for as long as you like. I've an
LED Lenser Police Tech Focus which produces 115 lumens and charges my watches exceptionally well. Helpfully one can also use it to see in the dark.
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