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Three types of light sticks were compared as to brightness over a period of time. From left to right in the below photo, a battery operated Fun-Tastick Glo Lite ($2.48, but no longer available), a Walmart ($2.67 for two) chemical green glow stick, and an Ocean State Job Lot (cheap overstock and excess inventory store) 99 cent glow stick. The later was turned out to be red instead of green and unfortunately it slowly leaked after being snapped to activate.
(Click any image for a larger photo.)
The exposure was the same for the first three photos at 1/20 sec. where the chemical sticks decreased in intensity so that they were no longer seen by the camera. The second photo is after one hour, the next after 4 hours. The last photo is a repeat of the third but at 1/5 sec. (3X exposure) to better photograph the difference between the sticks. Since the visible eye adjusts to the dark, the decrease in light in the photos looks more drastic than apparent to the eye. But the chemical glow sticks really do not last long enough for practical use on a kayak. The battery glow stick dropped in intensity to about 1/3 its initial intensity after 4 hours, but if the batteries are rested for several hours the brightness is almost back to normal. So it could be used for several night paddles before the brightness was ineffective.