That's very reassuring :) I think im going to go with the XR15's & Blades. I like the look of the combo hung from the ceiling lol
Well that brings up a point.
Many par differences can probably be attributed to different hanging heights and distance from light to water surface.
So I second mrpontiac80.. :)
If I remember correctly xr15s gen 6 ( height will depend on gen and lens angle ) are a wider angle than the blades. Well blades are listed as 95 degrees.
Radion G6 increases output from an impressive 110.5 degrees in the G5 to a staggering 126.3 degrees.
And I'm pretty sure what is considered normal height for stand alone G6s is generally wrong.
Due to popular demand (i.e criticism) they did come up with a narrower angle lens replacement.
Doing a 48" photon simplifies things.
Now you said your tank is 48" and 21" deep.
How wide?
In some instances this measurement needs to be taken into consideration.
Like if real wide you may want the puck/ bar thing to spread the light out a bit.
Next it depends on ones " color" preference and the lights color design.
Like if one prefers the blue look you don't get the " pro" version if the Radion and shut off 1/2 of the color.
Same w/ your blades.
Compared to your ai prime on full about 100w total to your upgrade to 400 plus watts for the Radion,/ blade
250 listed for the Photon.
As to your orig. question "properly" determine isn't the same as guesstimating.
Properly would be in tank under water .. but of course you need somewhere to start. As unpopular as it is watts per gallon on normal tanks has "some" validity. Unfortunately it is more likely you will buy larger than needed lights. Fortunately most leds are easily dimmed.
I'll guess you have about a 100gal tank. 300 watts of good leds should do it..
As you have been doing, checking around is the addendum to this guess.
The reefbreeder is "only" 250w rated (honestly not sure that is real world) but generally punches above its class via lensing and concurrent less waste. But again, you start shutting channels of... well you get the idea.
What would t5 or mh users use?
54 x 8 tubes,, 2 250 ( or 2 150w) mh bulbs?
Both have about the same overall inherent efficiency ( in reg bulbs approx 100 lumens/watt. Note though current leds are 50% more efficient at like 150 L/W and 100l/w Also lumens are not a good measurement for reef centric bulbs but used as a proxy of efficiency) where leds have better focus (less waste).
but again.. at full.