Ok, gotta chime in here. New metal halide lighting is almoast as efficient as T5/PC (remember, PCs are just dual T5s) now a days. Lets toss some numbers down. A dual 96 watt PC consumes about 210 watts of electrical energy between lamps and ballast. A 175watt electronic metal halide system consumes about 205 watts of energy between lamp and ballast. A quad 39watt T5HO fixture consumes about 180 watts of electrical energy between lamp and ballast. I'm trying to compare 3 systems for a 3foot tank span. Obviously numbers change if you use different bulbs, but these should be a close comparison.
Now, if you compare the Photosynthetically Available Radiation (PAR) from fixture to fixture is where the real decision lies. The 2xPC puts out 230PAR, the 4xT5 about 255PAR and the metal halide about 280PAR. If you go with efficiency of electrical energy/par you get an efficiency of 1.10, for the T5 1.42, and the MH 1.38. As you can see, T5s are the most efficient at converting Electricity to usable light energy, followed VERY closely by MH. PCs have a pretty significant dropoff, mainly because their reflectors are not as efficient. The 175watt MH fixture puts out a lot of heat, yes, but it also delivers more light. Even T5s and PCs get hot, so don't think they're light years more efficient than MH.
Also, one thing of note, the older designed Magnetic ballasted 150watt MHs consume about 235watts of electrical energy for nearly the same PAR and an efficiency of 1.19. Still more efficient than PC but not by much.
Also, for those who're wondering, PAR is a significant measure because it actually compares the amount of light delivered along the photosynthetic spectrum used by zooxanthellae. Just comparing Lumens (raw light) per watt is not a good measure of a bulb's effectiveness. Going by Lumens per watt, Halides are ahead of T5s, but some of that light is wasted. Hope that clears some stuff up
And as a point of fact, many SPS keepers who want the most light for the least energy are shifting to a 6 tube T5 setup. Gives them similar amount of PAR compared to a MH solution at a slightly better electrical efficiency. Although then there's the environmental issue of disposing of all the toxix phosphors in 6 T5 tubes compared with 1 or 2 MH bulbs every year. Lighting has come a long way in the last decade or so and our choices as aquarists are all good
Now, if you compare the Photosynthetically Available Radiation (PAR) from fixture to fixture is where the real decision lies. The 2xPC puts out 230PAR, the 4xT5 about 255PAR and the metal halide about 280PAR. If you go with efficiency of electrical energy/par you get an efficiency of 1.10, for the T5 1.42, and the MH 1.38. As you can see, T5s are the most efficient at converting Electricity to usable light energy, followed VERY closely by MH. PCs have a pretty significant dropoff, mainly because their reflectors are not as efficient. The 175watt MH fixture puts out a lot of heat, yes, but it also delivers more light. Even T5s and PCs get hot, so don't think they're light years more efficient than MH.
Also, one thing of note, the older designed Magnetic ballasted 150watt MHs consume about 235watts of electrical energy for nearly the same PAR and an efficiency of 1.19. Still more efficient than PC but not by much.
Also, for those who're wondering, PAR is a significant measure because it actually compares the amount of light delivered along the photosynthetic spectrum used by zooxanthellae. Just comparing Lumens (raw light) per watt is not a good measure of a bulb's effectiveness. Going by Lumens per watt, Halides are ahead of T5s, but some of that light is wasted. Hope that clears some stuff up
And as a point of fact, many SPS keepers who want the most light for the least energy are shifting to a 6 tube T5 setup. Gives them similar amount of PAR compared to a MH solution at a slightly better electrical efficiency. Although then there's the environmental issue of disposing of all the toxix phosphors in 6 T5 tubes compared with 1 or 2 MH bulbs every year. Lighting has come a long way in the last decade or so and our choices as aquarists are all good
