you can also raise the humidity by simply placing a bowl or bucket (depending on size of area) of water in the grow area. You can further increase it by adding a bubblier to the water to aerate it. This method how ever has many variables including exhaust speeds, overall temps, how wet your soil or media is, how large your plants are, etc. this method works better with small areas but is hit or miss on how high the humidity will actually go.
I am using a 4 bulb 48" florescent fixture with alternating daylight and warm light tubes. The smallest plants are on the ends where the light power is greatest and the larger plants are in the middle. Soon I will have to raise my lights and the smaller plants with it. pics to come....
SC