LED can pop the color of coral unlike any t5 can do. As far as the spread, my understanding is that it’s tough to beat t5 on that front, though LED bars can be pretty close.
I wouldn’t go back to t5 just because I can achieve the same or better par from my led bars and the color pop on my sps (walt disney for example) and of course, zoanthids.
Some people that have sps only tanks don’t need that distinct pop and depending on the coral, enjoy the look of it over led only. Blue plus t5 is an attractive bulb but I am seeing colors in my colors that i didnt see when i had my ati sunpower up. I also blended t5 and led and only noticed the pop when t5 went off in the evening
I think there are two ways to look at lighting.
1) Color and appearance to us
2) Food and coverage from the coral's standpoint
I personally believe that LED's leave a lot to be desired from a coral's standpoint. Sure LED's can grow corals just fine, its been proven time and time again, I have no arguments that it can't grow corals. My thought process takes me down a completely different route. Maybe its just splitting hairs at this point, maybe its the itch to understand why there seems to be a difference in accountable experience through anecdotal evidence, but in the end I think there is something left on the table in terms of the health of our corals.
When you talk to people who've been in this hobby for decades, you hear first hand accounts that Metal Halides and T5's grew corals faster and healthier than LED's ever have for those people. Some of this can certainly be chalked up to how easy/difficult LED's can be set up, but I believe there is more to it than that.
So lets think about the question, why would T5's and Metal Halides be any different?
I have a feeling that if you put a frag of the same coral under the same water conditions and same par where one frag is under a Metal Halide or T5 light, and the other is under a LED light, you'd not only see better growth, but healthier tissue from the coral under the T5 or Metal Halide light. This is an experiment that I'd love to try one day. I'd love to start experimenting and plan on building out a small area in my house for this specific reason. I hope sometime in 2026 I'll be able to start a few experiments.
If you ask me, I'd expect this outcome due to the simple fact that Metal Halide and T5 lights create such a broad spectrum of light versus LED diodes only creating specific frequencies. I know there are studies out there that prove corals use two or three specific wavelengths of light for energy, but my theory is that due to modifiers in the water such as water clarify, shading, ect, that these wavelengths get modified to a certain degree thus affecting the efficiency of the energy process of the corals. I also believe that the can be an argument made for the other spectrums of light helping the countless other organisms that live within our aquariums. I believe a healthy aquarium must be comprised of a healthy eco system, not just the fish and corals. I think its ill-considered to think that other organisms within our aquarium do not have any affect on our corals.
As far as spread, I think the hobby is starting to see the lack of spread from an LED standpoint as an argumentative point as to why T5 and Metal Halide's were just regarded as an all around easier lighting solution to aquariums. Due to this, I think we have and will continue to see improvements to LED fixtures in this area which really does help to bridge the gap between these new LED fixtures and Metal Halide and T5 fixtures. I just think that at the end of the day, LED's will always fall short of the mark set by Metal Halides and T5's because there just isn't a way to fully replicate a full spectrum light source with LEDs.
Another point that I wish to explore more through metal halides is the infrared light spectrums given off by these fixtures. But that's another discussion for another time.
