How Cold Temperatures Affect Chemlight

If you have seen The Lord of the Rings, you may remember what Sam used against Shelob: the Phial of Galadriel. The equivalent in the real world is the Chemlight made by Cyalume Technologies. Typical headlights and torches use Lithium or NiMH batteries with reduced efficiency in sub-freezing temperatures. For winter trips, I carry a few Chemlights as backup light. I’ve contacted Cyalume to know how cold temperatures affect the Chemlight and a Customer Service Representative replied:

Our products are designed to be used at 24°C. Every 10°C drop would halve the reaction kinetics, and every 10°C rise would double the reaction kinetics. Consequently, the Chemlight at 14°C would be half brighter but it would last twice longer. The Chemlight would freeze (one or more liquids will become solid) at temperatures between -20 and -30°C. In addition, the yellow light produce more light than any other colours. I would therefore recommend you to choose the yellow HI (high intensity, 30 mn.)

Based on that, I draw a chart in order to estimate the light duration:

In practice, I used the yellow HI Chemlight to look at my map inside my freezing tent overnight in order to save the Lithium-Ion batteries of my Nitecore headlight.