Summer, from what I understand, light means hand luggage only, saver-promo and e-deal are short time only promotion special deals, then the next category is a restrictive fare (ie penalty for changing dates etc), then the most expensive is the changeable one. It's so confusing isn't it!

When you book a flight, the terms and conditions for the fare you choose are displayed, you should read them then so you don't get caught out (you can still back out at that stage too).

Best of luck with it, I hope you find somewhere exciting to go and nice cheap fares to get there.