The sticks arrived, they were snapped, and everyone agreed they were not as bright as last year. There are usually only two reasons.

They were warm

Chemistry runs faster when it is hot. A pallet sitting in the sun behind a marquee, or a van parked in the open all afternoon, is running the reaction slowly before the ampoule is even broken — and it is spending life doing it.

The visible result is a stick that starts slightly brighter and finishes considerably sooner. On a long night that reads as dull, because the part everybody remembers is the end.

They were old

Glow sticks degrade in storage. The foil wrapper slows it down, cool storage slows it down further, and neither stops it.

Stock that has been in a warm store room for two seasons will be visibly down on fresh stock of the same specification. This is the real cost of the three-year price break.

What to do on the day

Keep them in a cool box or the coolest part of the building until they go out. It is free and the difference at the end of the night is obvious.

Do not put them in a fridge and then straight into a warm crowd expecting the best of both — cold slows the reaction, so a chilled stick starts dimmer. Cool storage, room temperature at handout.

What to do next year

Buy the quantity you will actually use, and ask for the manufacture date printed on the outer so you can rotate.

If a supplier cannot tell you when stock was made, you are buying an unknown, and in a product that ages this is the one specification that matters most.