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How much light should I use in my grow room?

This will predominantly depend on the size of your grow room.

As general guide, use about 1000 to 2000 watts per square meter of growing area.

Rule of thumb is 1% increase in light = 1% increase in growth up to the light saturation point. The light saturation point is the point where lighter won't get a growth response. Because of heat problems, you are unlikely to reach this point with normal artificial HID lighting.

What is the best light to use, high Pressure Sodium or Metal Halide?

In trials, we found that High Pressure Sodium (versus Metal Halide) when used for an entire crop cycle, slightly but noticeably out performed Metal Halide. We have also found that High Pressure Sodium gives a marginally better yield if it used for the bloom phase and the Metal Halide performs slightly better during growth.

Our results would not justify purchasing both the lights for growth and bloom but this may not be the case with all species and strains. We also found that both types of lights used together yielded better results than either type alone. Given the choice between the two, we would recommend High Pressure Sodium over Metal Halide.

How can I tell if there is too much light in my grow room?

Yield will be reduced because the upper canopy of the plant will get too hot and burn. It will cause the running temperature to be higher than necessary and in extreme cases the plant will " shut down " and stop growing as it will be unable to cool itself down.

Excessive heat rather than too much light is more likely to be a problem when using artificial lighting.

How can I tell if there is not enough light in my grow room?

Your yield will not reach its full potential. The plants need light too so the leaves can manufacture sugars for the plants use.

A rule of thumb is 1% reduction in the light from optimal = 1% reduction in yield. In severe cases of light deprivation, the plants will be pale and thin and will be stretching toward the light

I have plenty of light but my plants are still stretching and growing during the flowering period.

This could be caused by excessively long light durations during the flowering period.

You could try dropping the light to ten hours, crank the conductivity up to about 2.6-2.8 E.C and use a high potash additive such as Superior Potash. Many growers open their rooms during the dark period, allowing extra light in.

If the room is not adequately sealed against light then there could be light inadvertently seeping into the room during the dark time. Any light during the dark time may cause the plants to stretch. If these are not your problems, then it could be the strain you are using or too high a nitrogen level during the flowering phase.

Do I need reflective walls inside my grow room?

You don't need to have reflective walls but reflective walls dramatically increase the light efficiency and therefore plant growth.

Non reflective surfaces absorb light which is therefore not available to the plant.

Rule of thumb is 1% increase in light = 1% increases in growth up to the light saturation point. The light saturation point is the point where lighter won't get a growth response. Because of heat problems, you are unlikely to reach this point with normal HID lights. Silver or white surfaces are the best to use.