By comparing them MH requires much more power than LED to attain the same amount of PUR. MH is less efficient and radiates light at 360 deg while LED is unidirectional and can be zoomed in with low angle lenses to penetrate deeper. MH is full spectrum so it does waste a lot of light energy while LED uses only the right frequency or color (blue) with some whites to please our eyes. For those with MH and add blue LEDs, I believe they use the LEDs for moonlight. Otherwise, it is just aesthetic to have more blues.