It can be any number of things. Higher end systems tend to use higher quality reflectors, electronic ballasts, better quality materials for the enclosure, better build quality, better longevity and generaly look better.
Cheaper lights tend to use cheap reflectors, magnetic ballasts, and lower quality materials. Most are mass produced in China by people who have likely never seen a reef tank.
Lighting is one department where the old axiom "you get what you pay for" is true.
This comming from the guy with the Odyssea lights
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