looking on the bright side / seeing the glass half full

[Mnemon]

What's the difference between the two expressions? looking on the bright side & seeing the glass half full

Could they be used interchangeably?

a- Looking on the bright side, I'll have plenty of time to start my own business now that I'm unemployed.

b- Trying to see the glass half full, I'll have plenty of time to start my own business now that I'm unemployed.

 

[jutfrank]

Although the meanings are related, the difference is in the way we use them. Below I give some brief description and examples of common use:

1) look on the bright side is a semi-fixed verb expression, often used in imperative form to offer consolation to someone.

Look on the bright side—at least you'll have some free time.
Try to look on the bright side. I mean, it's not the end of the world, is it?

2) Is the glass half empty or half full? is a proverbial, rhetorical expression, used to express that a given situation may be equally treated with a pessimistic or optimistic attitude. This proverb is so well-known, however, that it can easily be indirectly referenced using other ways of expression:

Are you a 'glass half empty' or 'glass half full' kind of person?

 

[probus]

I can't resist a joke here. The optimist says "The glass is half full." The pessimist says "The glass is half empty." The conservative says "Who the h*ll drank half my water?"

 

[Tdol]

Just half? Doesn't sound like a modern commentator as they're telling the truth.