6. LIGHT

High Intensity Discharge lamps are the best solution for inside growing. These HID lamps are available in three “tastes”:  High Pressure Sodium (HPS), Metal Halide (MH) en Mercury Vapor. HPS gives a somewhat yellowish light.

The HPS bulb is by far the most commonly used by indoor growers. Philips has several types available: 

-          MASTER SON-T PIA GREEN POWER (The most efficient SON lamp with the highest growth/lumen efficiency per watt. Enhanced pressure improved the light-efficiency close to 150 lumen/W).

-          MASTER SON-T PIA AGRO (Special spectrum with more blue-emission resulting in more compact plant growth, especially suited for relatively low levels of light).

While blooming, do not use bulbs that give too much of a yellowish light, like SON T Plus bulbs. With such a lamp the harvest will be about 20% lesser. Also do not use the MASTER SON-T PIA (used for streetlights) but the MASTER SON-T PIA GREEN POWER. Furthermore, Philips advises to combine HPS bulbs with MASTER HPI-T PLUS bulbs in case of growing without any sunlight.

In my opinion one 400 watt lamp per square meter is exactly right. But a lot of people have great harvests with a 600 watt lamp per square meter. It all depends on the circumstances. If growing in a big hall where you have perfect control over temperature and humidity a 600 or maybe even a 1000 watt bulb will do great. But, if you grow in a room of an apartment it is often difficult to keep the temperature and humidity acceptable. In such a case better to choose for the 400 watt per square meter. According to Philips, bulbs can be used for about 10.000 hours without unacceptable loss of light. When lamps are used 12 hours a day they can last for more than two years.