LED Grow lights have come a long way in a very short amount of time. The technology required to produce enough usable light wasn’t obtainable until just recently. Unfortunately for consumers many LED companies toted their LED grow lights as more powerful than HID (high Intensity Discharge) lights when they were not. These early misleading statements lead to a negative consumer sentiment that lasts to this day.

I’ve been growing with and testing LED grow lights for 4 years, I’ve tested many of the early LED grow lights that were more than disappointing and often catastrophic to the test plants being grown under them. In the past year or so there has been a significant change in the LED grow light technology available and this has opened the flood gates to high quality, high powered LED grow lights on the market.

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At this point LED grow light technology though more expensive than traditional HID (high Intensity Discharge) lights, is now capable of replacing your current HID setup. There will be some skepticism to that statement but I’ve had over 8 grows with current LED technology and have found that I have had no loss in crop yields, in fact I’ve seen small increases in cannabis yields.

You don’t have to take my word that LED is as good as HID lighting, I’m going to explain the confusion over LED power output and you’ll see for yourself.

How to calculate LED wattage required to flower Cannabis plants

The traditional power measurement for grow lights has been Watts which has made things simple up until the development of LED. A Watt of power equals 1 Watt of power output of light. The confusion comes when you try to measure LED grow lights in Watts. In the case of LED, a Watt of power into the light isn’t a Watt of power out of the light. Since LEDs are much more efficient than incandescent bulbs we must use a different measurement to qualify the power being generated by the LED grow light.

You might have heard or read the term “PAR” related to led grow lights, this is the actual measurement of the useable light spectrum produced by the LED. You see LEDs get their efficacy from not converting as much energy into heat compared to incandescent bulbs. This means that more of the energy used by the LED grow light is converted to actual usable grow light.

LED Cannabis plants
LED Cannabis plants – Image Powered by how-to-marijuana.com

“PAR” stands for photo-synthetically active radiation which is light emitted in the electromagnetic spectrum between 400 nm and 700 nm while humans only see light wavelengths between 500 nm and 600 nm. Plants can convert light wavelengths between 400 nm and 700 nm to energy via photosynthesis. This still doesn’t tell the whole picture, we haven’t talked about the light intensity.

This is where things start to get a little more complicated. The next term you will need to know is “PPF” or photosynthetic photon flux, sounds like a Star Trek reference I know but it just means the amount of light produced by a light source per second. This leads us right to another term, “PPFD” which stands for photosynthetic photon flux density. This is the measurement of how many photo synthetic photons fall on your plants surfaces per second.

How are you supposed to figure out how large of a LED grow light you need? Well you could do the math which most people have no interest in doing, or you can use this handy chart to estimate. The average LED grow light draws about 32 watts to cover 1 square foot for flowering cannabis, we’ll use flowering cannabis to calculate power requirements since the flowering stage requires significantly more power. A typical HID light would draw about 45 watts per square foot just for comparison.

Quick Chart

Quick Chart
Quick Chart – Image Powered by powerlines.seattle.gov

1′ x 1′: 32 watts
2′ x 2′: 128 watts
3′ x 3′: 288 watts
4′ x 4′: 512 watts
5′ x 5′: 800 watts
6′ x 6′: 1152 watts

Estimation Based on 1 square foot per plant
# of Plants   Square Feet   Recommended LED Wattage
1                         1                                     32
2                         2                                    64
4                         4                                    128
6                         6                                    192
8                         8                                    256
10                        10                                  320

What do they mean when they talk about full spectrum light?

I opened this article mentioning “PAR” which stands for photo-synthetically active radiation. This measurement of light is often referred to as full spectrum light. Full spectrum lights are the wave lengths of light between 440 nm and 700 nm which includes ultraviolet and infrared. Cannabis plants use this whole spectrum to photosynthesize light into simple sugars.

When purchasing a LED grow light system, you will find that the higher end systems will all be full spectrum. Be cautious when investigating cheaper grow lights as manufactures sometimes claim to be full spectrum but don’t provide IF and IR LED Chips in their units.

Is full spectrum light absolutely a requirement? You can get away without ultraviolet and infrared but this could leave your plants open to unwanted issues such as molds and mildews. Ultraviolet light is natures sterilizer, it’s even used to kill virus’s. When growing in a small area such as a grow tent it really is important to have ultraviolet to mitigate the risks of enclosed growing.

spectrum light
Spectrum Light – Image Powered by plazilla.com

Full spectrum LED lights generally have two operational modes; vegetation and flowering. In Vegetation mode the grow light will use 40% less energy and use less red light. This is because vegetation doesn’t require as much energy as flowering a plant. As well flowering plants require more red light to grow fat health buds. When you’re ready to start flowering your plants just flip the operational mode over to flowering and you are done. No need to change light bulbs.

One thing is for sure a full spectrum LED grow light will produce a larger yield than a LED grow light that isn’t full spectrum. I’ve grown with both options and the full spectrum option really takes LED grow lights to the next level.

Light color by Nano Meter.
⦁ Yellow – 580nm
⦁ Orange – 610nm
⦁ Red – 630nm
⦁ Deep red – 660nm
⦁ Blue – 460nm
⦁ Royal blue – 430nm
⦁ UV – 410nm
⦁ Infrared (IR) – 730nm

Managing Heat

It is true that LED grow lights produce about 40% less heat than traditional incandescent light bulbs. LEDs achieve this by producing only useful light spectrums for growing plants, it cuts out all the white light which greatly reduces the heat generated.

LEDs which is short for light emitting diodes, are solid state electronics. As with all electronics heat is the enemy. With LED grow lights excessive heat means ware on the electronics. LED chips that are normally rated for 50,000 or more hours can have their lifespan greatly reduced by overheating.

Quality LED grow light manufactures engineer their units with fans and heat syncs which greatly dissipate heat. Heat is drawn into aluminum heat syncs where cooler air drawn into the light unit and over the surfaces. This brings a great reduction in heat to the LED grow unit as well as the whole growing area. The heat left over from the grow light is generally easily managed with simple ventilation of your grow area. I find that my 1000-Watt LED panel produces a temperature that sustains the grow area at 85 degrees Fahrenheit or 30 degrees Celsius without extra ventilation or fans.

Spreading the light around your grow area

LED grow lights make use of lenses to direct light out of the LED structure and into your plants. All LED’s have a primary lens to deal with this. Some manufactures add a secondary lens to their grow lights to direct the light into wider beams to create more coverage or into narrow beams to create more intensity.

Each time a lens is added in front of an LED the power of the LED is reduced by 8-10% but the increase in efficacy for the plants great out ways the slight energy loss.

Spreading the Light
Spreading the Light – Image Powered by just4growers.com

These optics are generally made of plastic or glass and tend to have a focus of between 90 and 120 degrees.

Some deceptive manufactures advertise that their lenses increase the intensity of light that is passed through them but this is not possible. The intensity can only be increased with more power while the lenses decrease intensity by expanding the lights foot print or increasing intensity by reducing the foot print.

Is the cost of a LED Grow light worth the reward?

It is true that the upfront investment in a LED grow light is higher than a HPS (high pressure sodium) grow systems. The traditional HPS is just a fancy light bulb with a ballast to prevent flickering. The HPS system requires that the bulbs be replaced after about 6 months of continuous use. The HPS system also requires about 40% more electricity to function at full capacity compared to a LED grow light on Flower mode.

LED Grow Light
LED Grow Light – Image Powered by growweedeasy.com

LED’s have an expected performance life of 50,000 to 75,000 hours or 5.7 years of continuous operation. That’s a load of grows, couple that with the 40% decrease in electricity costs and you have a pretty easy answer. But the savings go further. Due to the lower operating temperature of an LED grow light your grow will require less environmental air conditioning. You will require less energy to manage the temperature and humidity inside your grow space.

TIP: Looking to buy seeds? Visit the ILGM marijuana seed shop

You can see pretty quickly that the high upfront cost of LED grow lights is made back over a short time of operation.

The time of LED grow systems is here! Over the next year or two more and more people will invest in this technology and that will fuel even more development. I wouldn’t wait for any more improvements because LED technology is already capable of increasing your cannabis yields and potency. Do a little research, read some led grow light reviews and you will surely be happy with your move over to LED grow lighting. If you’re a new grower then you’ll just get to know the simplicity of LED as the go to technology.

Bud Durden is an expert writer, grower and entrepeneur.

Read a full 2017 LED light review on his homebase Budsgrowguide.com

Marijuana stays in the news, and Alice is always ready to keep us updated. A world traveler and lover of freedom, Alice knows what is going on, no matter where she roams. She specializes in marijuana legalization stories across the globe, with up to date... [read more]


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  1. By Queen Frostine ,11 Feb 2018
    Very helpful, thanks! Besides being effective & efficient, LED lights are more fun to look at. They remind me of a disco with strobe lights, haha. Like your plants are having a rave in their growbox ;)
  2. By Matt ,28 Jan 2019
    I use 3 x 5 metres of LED strip lighting in white, warm white and cool white in a grow box with silver reflective bubble wrap of dimensions 1200mm high, 700mm wide and 500mm deep. Plants are thriving on less […]Read More
  3. By Dee ,13 Aug 2019
    I found a herme after 4 -5 weeks of Flowering. I took it out of the tent as soon as I discovered it. How do I know if I got it out in time before it pollinated my other femmales?
  4. By Ralph ,24 Jan 2020
    What are your take on plasma lighting for growing
  5. By Danny ,05 May 2020
    I'm just starting a grow but I would like to know what tents would be good. What exhaust fans, would be good to use.
  6. By Bryan ,22 May 2020
    Best light for a 2by2by4 grow tent

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