Keep your plants a minimum of 4' away from the lights. I have some plants that shoot up and end up getting burned so you have to constantly monitor growth and rearrange them as needed. I have the lights on timers because there's a huge window in the grow room that allows a good amount of in for a few hours in the afternoon. I have them set to go on at 6am, off at 1pm and back on at 4pm until 8pm for a total of 14 hours of light. Some people like keeping the lights on for 16 hours but they are energy hogs. Karyn

Squirel cage fans block the light, an important consideration if some plants need 12 hours of darkness to bloom. The axial fans Paul is talking about do not block the light; you would have to rig up something else to do that. The axial fans that are quiet, tend to have low cfm. Because small axial fan blades have so little surface area, they need to rotate fast in order to move a lot of air. (Paul) " Electrical and computer fans at low rpm are virtually silent,..." (Lermer) "Electrical" fans? I had thought all fans were electrical, although I suppose there might be little elves with hand-powered fans. "Computer" fans? I don't know what kind of fan Paul has, (perhaps the original WWII-era Eniac); but in all the computers I have seen, the axial fans in them are too small to be useful for plant room ventilation. (Dcarch) "The computer type of cooling fan is specifically designed for ventilating and cooling." (Lermer) Silly me, I had thought all fans were for the purpose of ventilation and cooling. Please, tell me where I could get some fans that are not. Ripley's Believe it or Not might be interested. (dcarch) "Squirrel cage (centrifugal) blowers are specifically used to overcome backpressure situations as in pushing air thru ductworks. It is never used for general cooling purposes." (Lermer) Squirrel cage fans have that capability, but they don't have to be used in ducting; in fact they are rated for different lengths of ducting starting with none at all. Normally I wouldn't use them without ducting (because of the higher cost) but they do block the light. If you read what I said, my first preference was for an open door with a 16" pedestal mount fan from Home Depot. Telling someone to make holes in their door and install axial fans in them, without warning them about light leaks (in and out) is irresponsible. (dcarch) "Before you use a 16" fan to blow on your seedlings, say goodbye to them first." (Lermer) I said, pedestal mount; which means, the height is adjustable. Jon didn't say anything about seedlings. Those can be placed away from strong air currents. The bigger plants would appreciate the air movement (as any but rookie growers know). (Object 16) "PHOTOSYNTHESIS IS OPTIMUM at 70-85 degrees." (Lermer) That's an incredibly ignorant statement. Where did you hear that? Generally, he optimum temperature is 76F. For every two degrees above that, you lose about 10% of the plant growth. This isn't apparent to the naked eye, except at extremely high levels. Above 76F you will see more green leaves because the leaf surface area increases (leaves become thinner) to transpire/cool more; and the leaves at such high temperatures tend to be more full of water. Once you weigh the dried mass, you will significant reductions in yield at 85F. Although light-on periods should have at least 70F. http://www.umass.edu/umext/floriculture/fact_sheets/greenh use_management/gh_cool_growing.htm "For many crops, media temperatures for germination should be between 72F and 76F. After a crop is established, most plants will tolerate non-optimal temperatures more easily. Seed germination is not the place to skimp on heat." (Lermer) Adult plants can usually tolerate slightly lower or higher temperatures, depending on species (where they evolved). A few degrees above optimum is a lot more harmful than a few degrees below optimum. (Object 16) "Plant growth is mainly a function of total number of photons - a rough measure of light intensity is lumens, so have a look at both lamps, and decide whether one or the other has sufficient lumens." (Lermer) "Lumens" is a "rough" measure, true; very rough, because it is biased toward the center of the spectrum. HPS reads very high in lumens because it is mostly yellow spectrum. However lacking a better common measurement, "lumens" is a factor to consider; but you should also consider spectrum. Generally you want a full spectrum, between 400-700nm, blue (about 420nm) and red (about 675nm) are the most important. For that, CRI (color rendering index) is a rough measure.

I bought a ballast from a retail store in Ohio; and the ballast is a month old. The hum orginates at the top end of the handle and you have to wedge something between the ballast box and the handle to stop humming: I know ballasts normally hum but in this instance it's rather a harsh sound. I emailed Sun System as well: I have a defective ballast(Sun System X Econogro Remote Assembled Ballast); and I have a two year warranty: Where do I send my ballast for repair or replacement??? The retailer I purchased the aforesaid product from said I should send the product to you.????

I am trying to buy from Northern Lights at the moment.. well, almost at the point of demanding my money back. Don't give them any of your money!!!! I bought a 500W dual spectrum light from them 2 MONTHS ago and have yet to get the light. Apparently stuff was backordered and they didn't bother to tell me till I called and asked. They promised it was shipping that week, but that was 1 MONTH ago and I still don't have it! Plus, the shipping company has no record of any package shipped from their zip code to mine. Now they won't return my phone calls! I am 1 wk away from going to the BBB of Central Indiana, where NorthernLights already has an "unsatisfactory rating due to unanswered complaints". Wish I had looked that up before giving them almost $300 of my money.