This year saw four CFLs popping over the holiday period in our house. I have noticed it in the past too, and although I've never bothered to check it out, I suspect the reduced industrial/commercial load over the holidays results in the voltage creeping up to the peak permitted value, which old bulbs don't tolerate well.

I am replacing them with LEDs as they fail, so the failure may save me money, but it remains to be seen how reliable LEDs are. I suspect they will not be any more reliable than the CFLs were.

All UK mains appliances are supposed to be rated for at least 253V when our supply dropped to 230V nominal (+10% -6%)

Basically both UK and Europe are called 230V but UK leans to 240V and Europe leans to 220V. European lightbulbs don't last as long in UK unless they are marked 240V.

240V +6% -10% 226V-254V
230V +10% -6% 216V-253V
220V +10% -6% 207V-242V

I've yet to find a CFL that reaches its stated life, even ones that were left on 24/7. I used to date them when I fitted them.

My LED bulbs have dimmed significantly (or went more yellow) after about 3 months but after that the light appears roughly constant.

Both white CFLs and LED's rely on fluorescence to get the right colour which is the a point.

I've phased out CFLs in favour of LEDs (warm white) throughout the house now, and find the light much better. They are supposed to last a lot longer - but only time will tell! I've also swapped over to LEDs for all the fairy lights.

The problem with CFLs and LEDs is in the electronics. They both use switch mode power supplies in one form or another, and that involves electrolytic capacitors which don't last very long. They are the certainly the cause of death in the CFL ones I've done post mortems on and I expect no better from the LEDs.

LED chips don't last forever. I once read a paper describing the slow increase in forward voltage which causes them to run hotter and the luminance falls. That's not the whole story. The materials used have different coefficients of expansion and this causes minute cracks to form in the die.

The result is they tend to fade away rather than die.