LED Grow Light FAQ - Your Questions Answered

How much money will I save if I switch to LED grow lights? What size LED do I need for my grow tent? We get these question a lot and we are always happy to answer. Below we have summarized some of the most frequently asked questions that we get form our customers at GrowersHouse.

How much money can I save by switching to LED lights?

If you have a small grow room that measures 4' x 4' you will need 1 grow light with about 500 watts of power. You'll spend slightly more on purchasing an LED light, but you will save on electricity costs and bulb replacement costs.

Over the course of 10 years you would wind up spending $4,800 on your CMH lights and only $3,900 on your LED setup. We have discussed this in-depth here.

Can too much LED light kill a plant?

Yes, too much light from any source can damage your plants, though it will be extremely hard for the light to kill the plant alone. You will see visible cues of this as the plants are affected. Signs of too much LED light will include lightening of the leaf tips on only the top leaves. As this progresses the plant leaves will become crisp and burnt. Another sign of too much light is the buds will start to bleach white near the top. If you see these signs raise your light by 12 inches and that should solve your problem. Just remember, plants grow up, so raise your light up as the plants grow vertically.

What size LED light do I need for my grow tent?

This is one of the most common questions that we get on our website and in our store. The answer depends on the size of your growing area and power of your LED lights. A 5' x 5' grow tent can be covered by a single 750W grow light. Take a look at the chart that we have created here to help answer this question - How Many LED Lights Do I Need for My Grow Room?

What are the best LED grow light brands?

The best LED grow light for one person may not be the best LED grow light for another. What we mean by that is 'best LED' can be measured by total output (PPF), efficiency (umol/J) or even some other measurement like how thin, light or modular the LED light is. Now we know this is not the answer you want to hear, so we're going to break down the best LED grow lights by different measurements:

You can read the details for our top recommendations in different price ranges in our Best LED Grow Lights of 2021 Comparison & Review Test.

Best LED Grow Lights By Efficiency:

1. HLG Scorpion Diablo 650w @ 2.86 umol/J


2. HLG 650R @ 2.75 umol/J


3. Gavita Pro 1700e @ 2.70 umol/J

Best LED Grow Lights By Total Output:

1. Growers Choice ROI-E720 @ 1,895 PPF (umol/s)


2. HLG - Scorpion Diablo 650w @ 1,874 PPF (umol/s)


3. Gavita Pro 1700e @ 1,764 PPF (umol/S)

Should I run my grow lights at night? Can I leave my grow lights on 24 hours/day?

Turning lights on for part of the night will accelerate vegetation and flowering. Light cycles are expressed as X/Y, where X is lights on and Y is lights off. Common cycles are 12/12 and up to 18/6. A light timer can turn the grow light or lights on and off at the times you set. Do not, however, leave grow lights on 24/7. Continuous light will cause plants to dry, at least stunting growth but quite possibly killing them.

What color should my LED lights be at night?

In general, newer, quality LED grow lights are full-spectrum lights—that is, they closely mimic sunlight. Check the manufacturer's specs for your light fixture. We're adding light tests all the time. Many LED grow lights are adjustable for spectrum. Seldom do we answer a question with a question, but here it's necessary: In what phase are your plants?

Propagation: More blue especially, and some red.

Vegetative: Just go with a full-spectrum LED light. Vegetation also benefits from more green and yellow as plants get bigger and fuller, to better penetrate the canopy. Full-spectrum lights have these wavelengths.

Flowering: More red especially, and if possible, more blue.

Do LED lights take longer to flower than CMH lights?

Both full-spectrum LED lights and CMH lights are strong performers for flowering. How long flowering takes depends on a lot of factors, including hours of light, temperature, humidity level, and the light spectrum that bathes the plants. Older "burple" LEDs, with only blue- and red-emitting diodes will not flower as well as a CMH (ceramic metal halide) or a newer full-spectrum LED fixture. Both CMH and full-spectrum LEDs approximate sunlight, so they include blue, red, and good vegetative wavelengths, such as green and yellow.

Many high-quality, newer LEDs allow you to adjust the spectrum; lower-cost LEDs usually do not adjust. For flowering under an LED fixture, adjust the spectrum to give plants considerably more red and some additional blue. Adjustable LED fixtures sometimes have pre-set levels for propagation and flowering.

Although good for flowering, CMH grow lights do not allow for adjusting the spectrum. To add red during flowering, consider replacing the CMH bulb temporarily with an HPS (high-pressure sodium) bulb that is compatible with your CMH fixture. It will provide higher levels of orange and red and accelerate budding and flowering.

How should I adjust my growing lights throughout the growing cycle?

With the right adjustments, you can improve maturity during propagation, vegetation and flowering. Not all light fixtures are adjustable as newer, high-quality LEDs are. That means you'll have to look at the spectrum characteristics for each light before buying. Manufacturers include this information on the package and online. You want a light that comes as close to mimicking daylight as possible—full-spectrum light.

In general, for optimum results, here are wavelengths preferable in each stage of the cycle. Blue and red are useful in all phases:

Propagation: Extra blue and some red; a limited amount of ultra violet can increase terpene production, but too much can damage plants.

Vegetation: Lots of blue, green and, when plants become fuller, yellow, which penetrates the canopy to feed lower parts of the plants.

Flowering: Definitely more red, and a little extra blue.

Adjustable LED fixtures make this process easy. MH and CMH are both good for propagation and vegetation. With MH and CMH bulbs, however, you would have to replace them during flowering with an HPS lamp to get more red and orange. The fixtures must be compatible for the multiple types of bulbs. Fluorescent lights do well in propagation because their spectrum is blue-white, and during vegetation. For flowering, however, you may want to replace a standard white tube in the fluorescent fixture with a red tube, a fairly inexpensive adjustment.

How much will my LED grow lights add to my power bill?

Let's look at power consumption for an LED fixture suitable for up to a 3' x 4' veg space, the California Lightworks SolarXtreme 500. It would add about $19 per month to your bill, or $228 per year, at the average U.S. power cost of 13.19 cents per kilowatt hour. Twelve hours daily is typical usage. Use it longer and your cost would rise, as it would with a higher electrical rate.
The higher the wattage on a light, the more it will cost to run.

What are the best grow lights for small closets and grow tents?

The California Light Works SolarXtreme 250 LED and Horticulture Lighting Group HLG 100 V2 LED are two of the best LED lights for ultra-small grow spaces. We recommend these for spaces as small as 2' x 2'.

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