the mercury lamps produce light good enough for the last two weeks of the plant....they are called Mercury Vapor lamps and they are used mainly for aquariums.....what these bulbs do is to produce light similar to the one the sun produces but the light they emit is rich in uvb rays....the uvb rays are harmful and thus the plant to protect itself produces more thc as a reaction......these bulbs therefore cannot be used for vegetation or flowering.....for vegetation use a MH bulb and for flowering an HPS.....if you like for flowering add a supplement to the HPS using a Mercury Vapor bulb of low wattage~around 75 watts for a couple of hrs a day....remember though they are harmful....you can do the job only with the HPS!