When seeing some of the Elaborate Christmas lights people are putting on
their homes, and noticing more people doing this, I'm wondering what
precentage of the population would have to decirate to the extreme,
before they caused power failures?

I realize this is a vague question, because it depends on the electrical
distribution system, pole transformers, and the capacity of the
generators. It also depends on the actual amperage of the lights,
whereas the older C7 and C9 bulbs consumed a lot more power than the
newer LED lights.

But still, there has to be a limit!!!
Add to this, the fact that there are a lot more energy consuming devices
used in winter, than in warmer weather, such as heat tapes, electric
space heaters, furnace blowers, and more use of regular lighting due to
short daylight hours.

I also wonder if the power companies have a reserve, to assist times of
very high demand?

For example, I know of a house that has so many lights, their house
glows almost as bright as daylight (at night). Someone who knows the
owner, said he estimated there are around 250,000 bulbs. And a nearby
park is decorated every year. It takes over 200 volunteers to put them
all up, and they claim they have over 7 million bulbs. I've seen both
of them, and they are awesome, but I'm glad I dont have to pay their
electric bills.

This park has five sections, all fed by it's own transformer and massive
panels. It takes a guy on a golf cart 1/2 hour to drive around and shut
everything down at closing time every night. The reason it takes so
long, is because they have to flip many individual breakers, because
certain lights are left on for security, and they have live reindeers
who need lights left on and their water tank heater has to stay on.
Plus some of this is computer controlled so the lights "dance" to the
music, and that alone takes a lot of time to shut down.