very true. uv rays ,which metal halide lights produce will make your babies frost up,so if pos use a hps with your mh into flower but if not feasable then put the mh in for last 2-3 weeks, you,ll notice a big difference or you can get uv lights from pet stores,for aqaurium tanks etc..... do the job nearly as good as mh lights,not quite but good enough.
I have talked about this many times in the past on this site and it is the sole reason I use the Ceramic Metal Halide during flowering and also VEG.