plug them in theres a way to tell by looking but i cant explain the technical shit.. only if i saw it i could tell.. just google what each looks like.. the insides of the lamps are very different and easily to visually differ
hps's tend to look like a long tube sort of. mh's have more of a bulbous shape in the middle usually. if you plug them in. the mh puts off blue light and the hps puts off orange