Best Growing Conditions
The best growing conditions for hydroponic plant growth rely on light, temperature, humidity and atmosphere.

Lighting
Plants naturally depend upon sunlight to grow so lighting is one of the most important things for successful indoor growth. Horticultural lighting is becoming more economical and cost effective.
The most efficient way to provide this is in a darkened environment where all the lighting can be timed and provided on a schedule. Alternatively, if growing in a greenhouse, the lighting can be timed to provide extra hours during the darker months of the year.
A very important thing to consider is the amount of light reflection in the growing area and getting the most amount of reflection in the room will provide an effective amount of energy.
Temperature
Most species of plants grow best between 20-28 degrees centigrade, with the optimal value being in the mid 20's. The lighting used for growth also provides heat so during this period is is relatively easy to maintain the ideal temperature.
There can be times where the heat becomes too high and there are a variety of extractor fans that can help to reduce this. The fan can be linked to a thermostat to ensure that it switches on and off according to the temperature in the grow room.
When the lights are off the temperature will lower, especially in the colder months of the year. For these times it is important to have heating, which can also be controlled by a thermostat.
Most plants do best when the ambient temperature is kept at a consistent level and with a combination of a fan, a heater and a thermostat this can be fairly straightforward to achieve.
Humidity
Humidity is the measure of water vapour in the air and is important to control to ensure the health of your plants. If the growroom is too humid for lengthy periods it can result in the growth of mould such as Botrytis. Mould can quickly spread and damage your plants.
A device that can help to monitor this is a hygrometer. This instrument is mounted on the wall and will constantly analyse the humidity. Ideally it will be lower than 50% and if it does go above this an extractor fan will help to reduce it.
To reduce the likelihood of high humidity ensure that any spilled water on the floor is quickly mopped up.
Atmosphere
Plants rely on carbon dioxide to survive, just as animals rely on oxygen. Just as we would struggle if left in a sealed environment, plants will also suffer in the same way. So it is important to ensure there is a constant and efficient supply of CO2.
One method of this is to ensure that there is an airflow into the growroom. Leaving a door or a window open can achieve this but it will have an effect on the temperature.
Alternatively, bottles of CO2 can ensure the plants can effectively breathe and a
regulator can monitor the levels in the growroom and release it as and when required.