how high to hang radion led light

[REEFER1981]

i have 24 by 24 by 18 45g cube just got radion need to know a good height to hang light being the tank is only 18 deep thanks for amy help

 

[scarface70706]

8 to 10 inches off the surface of the water sounds about right but i could be wrong. didnt the fixture come with instructions for height?