What is HQI lighting?

[civileng68]

How good is HQI lighting in comparison with MH?
I have 250 watts of MH lighting and want to add more power but I love a light an Aqualight Hang on 150 HQI light.
I love the Hang on setup so I was wondering if this light would be beneficial to my corals in adding power along with my current 250 watt MH.

 

[reefnut]

HQI is a type of MH. Typically it refers to a double ended bulb... which are generally more efficient than the standard single end bulb.
I read in a different post that you have a deep 55g?? If so, the 150w MHs may not give you the penetration needed. What is the overall goal you're looking for??
Sounds to me like you would be better off to add a second 250w MH??