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Many plants, especially flowering plants are triggered by the hours of daylight or darkness and the strength and spectrum of that light.

For most purposes, a plant in vegetative growth is usually looking for 18 hours a day of light.
Changing the light to 12 hours of daylight each day will usually trigger a plant to go into flower.


In the summer when the sun is high in the sky and the days are longer, the sun is more toward the blue end of the spectrum. This is exactly what a plant in the vegetative stage likes.


As the days get shorter, the sun gets lower on the horizon and has more of the atmosphere to shine through, which makes the light more toward the red end of the spectrum which is what some plants recognize as time to start flowering, pollinating or getting ready to produce seed.


This is how different types of lighting can greatly influence how a plant will grow during any given stage of growth.


There are only a few main types of lighting that are used in hydroponics.

HID or High Intensity Discharge lighting:

There are 3 main types of HID or High Intensity Discharge lighting used for growing.


These are High Pressure Sodium HPS, Metal Halide MH and Ceramic Metal Halide CMH


These lights put out about the same heat watt for watt as a heater would. So good in the winter around here but not so good in the summer.

Most common for many years is the HPS or High-Pressure Sodium.

HPS light is toward the red end of the spectrum so is mainly now used for flowering.

MH or Metal Halide is more toward the blue end of the spectrum so is more used for vegetative growth.

Now there are lamps (bulbs) that will work in either a MH or HPS ballast called conversion bulbs. There are also ballasts that are switchable from MH to HPS so you only have to change the bulb to go from vegetative growth to flowering.

The newest type of HID lighting is called CMH or Ceramic Metal Halide.

These are supposedly out performing the others by having a more complete spectrum while using smaller wattage ballasts to do the same job.

Time will tell but from what I’ve seen so far, my money is on them. Literally.

Fluorescentge lighting:

This type of lighting has been used for many years, and still is to a great degree.

Now with higher efficiency lamps and ballasts the cost has gone up on equipment but energy costs are less to run them than they used to be.

CFLs or Compact fluorescent lights also give you pretty good bang for your buck because the wattage to light output is rated at about 4-1. Meaning that a 100w lamps will give you 400w equivalent light. However, I wouldn’t expect it to work as good as an actual 400w HID lamp and ballast.

LED lighting is easily the most efficient type of lighting.

They have been around for quite a while but are only lately becoming quite common for indoor gardening.

Depending on who you talk to, they work very good to not so great compared to HID lighting.

Good quality LED lights are still very expensive. Whether they are worth the initial costs depends mostly on your budget.

I personally don’t have much experience with this type of lighting until recently, so I’ll leave it up to the geeks in the forums to argue about.