Well… A halogen bulb has a Filament cable which heats up and produces light 
, it uses a small amount of halogen to allow the filament to get hotter increasing light output.
A LED is a semi conductor which controls the flow of electricity through it. In the middle there’s a junction which the electrons jump over and change into light.
If you’ve ever touched a halogen bulb whilst it’s on or you’ve just turned off, I’m sure you’ll know that they get very hot
halogens waste 80% of their energy as heat and only 20% gets turned into light.
On the other hand 
LEDs are the complete opposite they change 80% of their energy into light, and the remaining 20% is changed into heat.
An 18w halogen bulb emits around 220 lumens, while an 18w LED bulb outputs 1300.
So in comparison you can run one 60w halogen bulb for an hour or twelve 5w LEDs for the same cost.
So LEDs are a much more cost effective solution 
