Lights are what defines your tanks abilities for reef limits.
FOWLR lighting is almost irrelevent as long as you can brighten the tank and see in, the fish dont really care and they are not photosynthetic
In Reefs, the more intense the lighting source, the better for penetration of usable light for those photosynthetic critters aka coral. The pricetag to someone getting into the hobby will surley give you stickershock, but a nice light setup is critical for reef and coral keeping. Growing in the hobby is a great logic and certainly there is lots to learn, but buying more and more equipment with every step up can be very expensive. Cutting corners and trying to press the limits of what can be housed with each method of lighting delivery can lead to stress in the tank and in your head since the inhabitants are expensive and demanding for your tanks stability. Cheaper to buy a piece of equipment once rather then replacing every 6 months when you grow out of it.
That being said, the more extreme the specimens requirements the higher intensity of the needed light.
Figure something like a Kenya tree only needing somehting ligh 3 on a scale 1-10
Figure a Zoo needing somehting like a 4 or 5 for good growth and color
Plate corals, Open or closed Brains ect. "fleshy corals" would be in the 6-8 catigory.
Hard corals like SPS .( Acropora, Milipora ect. )need higher like in the 8+ catigory
Anenomes and Clams are what would define the top, being a 10 in photo intensity requirements for long term health.
strip lights-2
compact flouresent about a 5 or 6
T-5 would be 6-8 unless VHO then bumb that to 7-9
Metal Hailide would be the top, it would be the most intense lighting readily available for reefkeeping. It would be a 10
All the above numbers are to be considered more of analogies instead of steadfast rules. If you walked in an said i need a light that around a 6+ they would odds are know what you mean, but the whole above I just made up to explain how it works. Not the Gospel.
I hope this helps clear some of the fog around why some lights are better than others. Thats my two cents
