Usually, the first thing the grower must decide is what lighting equipment he will use depending on the space he has available. Unless this space is tiny (in case you would use CFL bulbs or LED equipment) most growers opt for the bulbs that offer the best ratio/lumbermen, whether they are HM (metal halide) or HPS (sodium at high pressure).
The power and spectrum of the bulbs used are also determined depending on whether we want the plant to grow or flourish. During growth, cannabis plants do not have a high demand for light intensity, although they do have daylight hours. Thus, we will need to illuminate them for a minimum of 18 hours of light a day to ensure steady and steady growth. For this phase, the luminaries – always of a white / blue spectrum – most used are CFL, LED, standard fluorescent or HM lamps.
During flowering, and to achieve good results regarding yield, the plant needs a somewhat redder spectrum and much more light intensity, so the lamps most used for this phase are high-pressure sodium vapor (HPS), lit for 12 hours a day and off for another 12 hours without interruption.
To have the temperature as stable as possible, and even to have a good ventilation system, it is recommended to turn on the lights during the night, which is always the day less hot. If necessary, air-cooled reflectors can be used, which lower the cabinet temperature by 4-6ºC.
For our 1.2 x 1.2 meter cabinet – and always looking for maximum performance – we would normally use a 400w HM bulb for growth (18/6) and a 600W HPS bulb for flowering (12/12).