7 girls in one 2X5 tent requires all of them be approximately the same height by the time they enter the bloom tent. I try to keep the plants within 1 inch of each other so they all experience the same lighting intensity. This requires occasional position changes within the tent if I notice one plant out growing the others. It is my version of "equal opportunity" within my agricultural endeavor. This step is one of the "fine tuning" operations which contribute to a standardized product. The effort spent during the preparation stages prior to bloom is worth it. During the grow stage with the two 150 watt HPS lamps, a hot spot immediately below & centered under the bulb develops. Raising the lamps spreads the light out but, weakens it. Plants at the periphery do not receive as much light as the ones immediately under the lamp. This requires the operator to move the plants around every few days allowing each a chance at the center. It's not to say the plants at the edge are not receiving enough light. They are. It is a relative thing. There is adequate light at the edge to successfully grow a healthy plant but there is more light directly under the lamp. So, you still have to move them around. [All other factors being equal, heat considerations are not discussed here] Plants grown outside don't have that problem. They are besieged by other hazards.
Question: If all you are doing is growing 7 plants in a tent each crop, why do you need two 150 watt HPS lamps. Isn't that overkill?
Ans: More is better in the lighting department. You really can't have too much. There are two important areas of concern when using artificial light. (I know I said I was not going to talk about heat considerations. I lied. I am going to talk about it. ) The obvious one is the heat air temperature in the growing area. A ventilation system with air movement is required. The second is radiated heat from the lamp itself. That quartz tube in the center of the bulb is extremely hot. (Look at the bulb immediately after turning it off. It is still glowing for about 20 seconds. The center quartz tube gradually cools off. That is a lot of heat energy to be that close to your plants even if contained.) The radiated infrared heat from the bulb is detrimental and is best avoided. I maintain a distance of 15 inches from the center plant to the lamp fixture and rotate the crop accordingly. I performed that task this morning. In three days the girls will be ready to transition to the bloom tent, all at the same height and set to go. All that being said; I am eagerly anticipating the practical development of high powered LED lamps and lower prices. At this time they are too expensive and not bright enough. (mostly too expensive) The electrical bill for doing all this now is about $30 month. LED's could reduce that by $25 month. I will have to perform a cost study to see how far in the future I will have to go to reach the break even point. I still have another crop or two left on these bulbs before I assign them to parking lot lighting duty. I'll address the issue again at that time.
Question: If all you are doing is growing 7 plants in a tent each crop, why do you need two 150 watt HPS lamps. Isn't that overkill?
Ans: More is better in the lighting department. You really can't have too much. There are two important areas of concern when using artificial light. (I know I said I was not going to talk about heat considerations. I lied. I am going to talk about it. ) The obvious one is the heat air temperature in the growing area. A ventilation system with air movement is required. The second is radiated heat from the lamp itself. That quartz tube in the center of the bulb is extremely hot. (Look at the bulb immediately after turning it off. It is still glowing for about 20 seconds. The center quartz tube gradually cools off. That is a lot of heat energy to be that close to your plants even if contained.) The radiated infrared heat from the bulb is detrimental and is best avoided. I maintain a distance of 15 inches from the center plant to the lamp fixture and rotate the crop accordingly. I performed that task this morning. In three days the girls will be ready to transition to the bloom tent, all at the same height and set to go. All that being said; I am eagerly anticipating the practical development of high powered LED lamps and lower prices. At this time they are too expensive and not bright enough. (mostly too expensive) The electrical bill for doing all this now is about $30 month. LED's could reduce that by $25 month. I will have to perform a cost study to see how far in the future I will have to go to reach the break even point. I still have another crop or two left on these bulbs before I assign them to parking lot lighting duty. I'll address the issue again at that time.
