If you take a T12 as being 1 on the WPG scale.
T8 a tiny bit more maybe 1.2x
PC CF as 1.5x
T5 as 1.75x
T5HO as 1.8x
You will be in the ball park there.
As an example:
when I had 1WPG of T8 I got growth at a reasonable rate but the tank still looked quite dark
when I had 1.75WPG of PC CF I got much much faster growth but the tank still looked quite dark in some areas.
I currently have 0.9WPG of T5HO and the whole tank is light and growth if anything is even better and faster than I had with the CF even though it is nearly half the WPG.
Then I have to factor in the different plants I had under each light, the length of photoperiod, differing CO2 injections, different fert regimes, distance above the tank and thats how I come to the (still very rough) multiples I have at the top of this post.
So in essence we know 2WPG of T8 grows anything. 3WPG will carpet well. Therefore 1WPG of T5HO will grow anything and 1.5-2WPG will carpet well
The LED test will come soon. lol but will be much harder to work out due to the complicated lighting schedule I will use with it.
The distance above the tank is quite an important one. stock lighting (within cheap canopies) is approx 2" from the water level in some cases which means that the light will be god where the lights are but the light spread to the eye wil not be brilliant. When the lights are raised higher the light spread to our eyes may make it look better but the actual light to the tank will be lessened.
Think of a torch. If you point it at the floor next to you you see a small but bright circle. If you move the beam away the circle gets larger but not as bright. So there isa balance between getting the spread and retaining as much intensity as possible. Therefore If you have dark areas then you can raise the light up an inch or 2. Adding a little more light will maintain the intensity from raising it. Alternatively raising the light away can lower your WPG if required whilst also giving a better spread.
So those people who already have more light than they now now they wanted don't need to rip it out and downgrade. They can just raise their light with the same lights and the spread will be better whilst achieving a lower light level within the tank. Arcadia suspension kits are only £15 from AE or you can use chain and S hooks like I have. The Arcadia kit will obviously look better.
AC