"On a lighter note": what is the meaning of this and how to use it?

If I say:

Wow! Diwali party, that sounds great; on the lighter note, who is sponsoring it?

Am I correct in using "on the lighter note"? I am using it as saying something funny/witty.
Please let me know, if it is wrong, the correct usage of it.

Solution 1:

No. On a lighter note generally means "On a less serious topic." In addition, the phrase is typically used with the word a, not the word the.

Example:

Many people have died during the War in Afghanistan. On a lighter note, where should we have lunch?

Solution 2:

Typically used as a formal way of gracefully switching from a serious topic to a less serious one.