You can’t burn the candle at both ends.

This saying is literally true.  You can only light a candle at the top.  It is incomplete though.  What it refers to is both ends of the day.  If you are up before daylight, you will not be fit to work much after nightfall.  If you work long into the night, you are likely to wake up after sunrise.  I am not going to go into the effects of latitude on hours of daylight here.

Candle flame Photo credit Wikipedia http://en.wikipedia.org/wiki/File:Candle_flame_(1).jpg

To be unable to hold a candle to someone
means to be inferior.

A flash in the pan is an expression from gold-prospecting.   All that glitters is not gold.  Something seen while panning for gold may not be gold at all or a very small amount.  A flash in the pan means something which does not fulfil its early promise.

It came to me in a flash.
A sudden brilliant idea, perhaps.  In a flash means quickly.

Flashing lights have all sorts of associations: blue ones on emergency vehicles, orange hazard-warning lights at the rear of cars and on top of large vehicles.  Disco lights flash too.  If no-one else is seeing flashing lights, blame it on a migraine!

Flashy is usually associated with wanting to be noticed.

The light of someone’s life.
Someone who makes their life brighter.  Possibly a favourite.

Can you shed any light on this?
An explanation is needed.

A riding light is found on a boat at night so other sailors can see it.

A rising star is someone with promise.

Snuffed out.  Candles may be blown out, in which case they tend to smoke afterwards or snuffed out by covering them to cut off the oxygen supply.  A life may be snuffed out too.

Went out like a light means fell asleep quickly.

Don’t hide your light under a bushel.
If you have talents you should use them.  A bushel was an old measure of the volume of dry goods such as grain. It was a container of a fixed volume.  A light here would be a candle or burning torch.

Matthew 5:14-16