CFL Lights in a Grow Box, and
Do Plants Create Humidity?

by Fred
(Exeter, N.H. U.S.A)

I am a first time grower and I have a few questions. My grow box is 2'x2'x3' I have a total of 8 26 watt CFL's, 2 65 watt CFL's , with a 14 watt LED grow panel. There is a 4" intake fan (55 cfm) and a 4" outtake fan (55 cfm), and 6 sides of mylar. My first that enough light for 4 tomato plants (my lights are 6500k for veg and 2700k replacement for the flowering phase). Second question, should I use the LED for the vegetative and germination stage? Third question, without any plants in my grow box and all the lights on I have a box temp of 68, a room temp of 64, and humidity at 35% in both. Will the plants create that extra 15% that I need to gain? I understand perfect humidity would be 50%-55%, is this true? Thank you very much!

Answer: Fred- tomatoes and most other garden plants do very well under 40 watts of light per square foot. I use this as a general guideline in just about every garden I set up or give advice on. You mentioned the "footprint" of your grow box is 2' x 2', giving you a garden area of 4 square feet. If you placed all of your CFL's into this space (338 watts total), your box would be lit at 84.5 watts/sq.ft..

With fluorescent lights (including CFL's), the light doesn't penetrate down into the plants very far. So, on one hand, the extra wattage will help the light penetrate down into the plants further, allowing you to grow slightly taller plants and still have them be healthy at the bottom. Instead of having a 12 inch effective growing distance from the lights, you may end up with an 18 or 20 inch effective growing distance from the lights (especially with mylar on all 6 sides of the box).

On the other hand, you have enough light in your grow box to take one of those 26 watt CFL's out and use it to grow your seeds/clones or small plants in the vegetative stage. This is what I would recommend. The vegetative stage requires less light than the flowering stage, but 14 watts will not be enough. As a general rule, I try to stay at 20 watts/sq.ft. or more for the vegetative stage.

One CFL would work well to grow four small plants up to about 8 inches tall from seed or clone. The 14 watt LED can be used for supplemental lighting in the veg area if you like. As always, the plants will benefit most from the light if you surround them with reflective material.

Since your box is only 3 feet high, you will certainly want to start flowering your tomato plants while they are still short....they will continue to grow during flowering. An 8 inch tall plant may end it's life cycle being 16 inches tall! Also, you want to make sure there is enough air movement INSIDE the box....this helps carry away oxygen when the plants exhale and also helps bring fresh CO2 in contact with the leaves for the plants to breathe in.

The ideal humidity is 50%, plus or minus 10%. In general, humidity that is too high is much more of a problem than humidity that is too low.... especially if your humidity level is only a few percent from being in the ideal range. If I were you, I wouldn't worry at all about your humidity level....but to answer your question yes, plants create humidity by exhaling water vapor along with oxygen.

This process is called transpiration- as water vapor exits from the leaves, it creates a little vacuum in the plant tissue, allowing the roots to suck up water (and nutrients). The plants may ADD humidity to your grow box, but if you have your intake and exhaust fans on constantly to control the temperature it will not be enough to raise the humidity level inside the box very much (maybe one percent).

As I said before, don't worry about the humidity level. Much more important to your success will be proper lighting, proper feeding, proper temperature control, and providing your plants a proper dark period when it comes time to force flowering. I hope this helps....Happy Growing!

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Do Plants Create Humidity?

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Sep 25, 2011
by: Blazed

seems to me like you are not growing tomatoes but are growing some marijuana, in that case your grow setup is nice, just put a bowl of water near a fan to increase your humidity

Jan 18, 2010
Benefits of LED Grow Lights
by: Richard

Running Costs: The main benefit of using LED grow lights is the lower running costs. The better ones on the market use up to 90% less electricity than comparable Sodium/HID bulbs. LED grow lights can be used as either a primary light source or a supplemental light and they will pay for themselves in around 6 months of heavy use. The expected life of a LED grow lamp is on average 100,000 hours. This is 10 to 50 times longer than a typical Sodium/HID grow light bulb.

Purchase Costs: Although initial purchase costs may be higher than comparable Sodium bulbs, the real costs are often lower because you don't need a ballast. Unlike fluorescent tubes and metallic vapor lamps that need a ballast to operate, LED grow lamps don't need a ballast. This eliminates a recurring cost from your grow room set-up.

You also don't have the extra costs of purchasing a reflector as LEDs have the reflectors built right into themselves. Grow Season. Since the Chlorophyll does not have to battle with unwanted light-waves, LED's can also be left on 24 hours a day without stressing your plants out. You can also use LED grow lamps to simply extend the day period of your light cycle by 4/6 hours during the Winter months. This extends your grow season to 365 days per year.

Benefits To The Environment. Switching to low energy, solid state lighting benefits the environment. The low power requirements of LED light sources make them ideal for self contained, solar or wind powered installations, particularly in remote locations. LEDs consume far less energy than standard light bulbs, leading to greatly reduced energy costs.

LEDs also require far less energy to manufacture than other light sources, reducing their environmental impact even further. Less Environmental Hazard- Metallic vapor and fluorescent lamps all contain mercury, a heavy metal identified by the U.S. Government as hazardous to the environment and our landfills. Our LED Lights do not contain mercury.

Targeted Light Output. Broad spectrum grow lights produce a lot of light waves that plants can't use efficiently. LED Grow Lights only deliver the colors of light used by plants for efficient and healthy growth.

Minimum Heat. LED grow lights are warm to touch and won't scorch young or tender plants as HID lighting can.

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