"Show me some evidence and I'll consider changing my stance. Metal Halide lamps are recommended for the amount of light they give off. The spectral content is leveraged only as a marketing ploy to discredit High Pressure Sodium lamps. And, it may be true that MH is better than HPS but at that point we are talking about blue light compared to orange light."

A CD spectrometer

Even with basis tests you can see that a Metal halide as a more complete spectrum hence why plants like them more. As far as I can see this whole thread has been centrered around the blue/red ratio. surely just growing under red/blue can only be supplemental in the long term. Yes it works, yes blue lights Veg lovely plants. Its fact now. The mix is very relevent as the plants thrive on both red and blue through all stages of growth, just like outdoor green. There is also a lot of research to show that the important characteristics of the finished product are better when treated with more of the light we cannot see. At the very end of the visible light spectrum. There is also a lot to be said about moonlight on a plants life cycle too. AS professional growers of commercial crops know to sow when the moon is high as the gravity as an effect on root development. Its these factors i think that are more important than a red/blue mix. WE should be looking towards continuos spectrum lighting.