I really don't know.

They gave Luna's old design to Fleur De Lis... Is there any logical reason for that?

The ponies of Ponyville were supposed to be scared of Luna. It'd be silly if they were scared of her season 1 appearance after she was defeated.

Maybe because she was a young pony when she was imprisoned in the moon and she "grew up" to her proper age in season 2? I have no idea...

I don't know
: |

I know why! Pick me! *raises hand and waves* *gets picked*

Okie dokie lokie! :D

*Ahem*

Princess Luna appearance changed because the creators/animators wanted her to look like she's matured since the last time we saw her in Friendship is Magic, Part 2.

No way...

She's matured since we saw her in Season 1, so she grew up and her look changed.

You're probably right, but it's not took long for her to age.

She may have been sort of "suspended" in time and remained younger while banished...she matured to, as Angrykitty said, her proper age and current appearance since returning. I think Queencold, Tawnyjay, and StarWarsFan pretty much have it. At least, that's MY understanding of it.

And yes, her older body shape is very similar to Fleur de Lis'.

Maybe during the time from the first ep to the ep she was in season 2 she had her birthday and grew?

Who knows that's the fun

I think she looked different because she got her magical power back after it was drained from her during the battle with the elements.

After Nightmare Moon was defeated, Luna's energy was sapped, and she reverted to a weaker form. (Digimon, anyone? XD)

i have no idea?

she was drained of her magic. both luna and celestia look more like normal ponies without magic