Best LED Grow Lights: Everything you need to know about buying and Using a LED Grow Light

Last updated: March 2, 2019 at 10:08 am

Cannabis under Led Grow Lights

Led Grow Lights are amazing technical wonders. There is no other way to produce as much light while using less electricity than other available incandescent options. Though LED’s have come into the mainstream in recent years as a viable grow option It wasn’t always that way. Early LED grow lights were not very powerful and LED to poor yields all while the LED companies were touting its amazing power. These early misrepresentations have left a lot of skepticism in place to this date about LED Grow lights.

LED Grow Light Technology Has Arrived

To be fair, LED grow light technology has caught up and even surpassed my expectations. I’ve been a medium scale grower for over 10 years and in the past two years I’ve tested many LED grow lights and now my grow uses LED grow lights exclusively. That’s how confident I am in the technology at this point. I’ve been growing full time with LED grow lights now for two years and have had excellent results. In the early days before newer technology took hold, I had a number of grows completely fail on me due to the poor LED grow light quality. But that’s all changed now, LED is finally everything it was promised to be. High powered, full spectrum and energy and heat efficient; I call that the growing trifactor.

Need Help Picking a LED Grow Light, check out our LED Grow Light Reviews

LED Grow Lights Save Money

It’s true that current LED technology is more expensive than traditional High Intensity Discharge lights such as High-Pressure Sodium. That being said you can grow your crops with no loss in yields with 40% less electricity and a lot less headaches dealing with heat issues in your grow space. At this point I’ve completed six amazing grows since switching to LED grow lights permanently.  Any up extra up-front costs from investing in LED are made back within 1 or 2 grows just in electricity savings.

I don’t expect you to take my word the LED grow lights are truly the way to grow your cannabis over HID lighting. I’m going to explain Led Grow Lights and remove a lot of the confusion you might have over wattage or power.

How to calculate LED wattage required to flower Cannabis plants

When you are using traditional HID lighting for growing your cannabis plants you talk about power in Watts. One Watt of power = one Watt of Light power. This is where it gets confusing with LED grow lights. LEDs are much more efficient at producing light power. In the case of LED grow lights one watt in is not equal to one watt out making it impossible to compare wattage numbers between the two different light options it would be like comparing apples to oranges. That means there must be another way to measure light produced by LED grow lights.

LED Grow Lights are Measured in PAR

So, what the heck is PAR? It stands for Photosynthetically Active Radiation. Par isn’t a measurement like “metric, feet or inches, it references electromagnetic radiation which is required by photosynthesis to convert light energy into chemical energy; in other words, plant food.

Coincidentally the light spectrum that is used by plants for energy is the same visible to the human eye. Light is defined by wavelengths of the electromagnetic radiation spectrum. There are wavelengths that are not visible to the human eye such as UV and Infrared which are still beneficially to plants. For example, a small amount of UV light is usually included on LED grow light fixtures because of its anti-microbial effect.  So, if PAR isn’t a measurement how do you measure the strength of an LED grow light?

Map of Par Lighting
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How are LED Grow Lights energy production measured?

If PAR is electromagnetic radiation spectrum’s, then how are LED grow lights measured? I know you were hoping for a simple answer but it’s not. The three measurements that count is PPF, PPFD, and DLI.

So, the first thing to understand about PAR is that it is the part of the electromagnetic radiation spectrum (light) that is useful to plants and algae to activate photosynthesis — it is NOT a measurement. What really counts is:

  • How much light the LED grow light creates?
  • How much of that light is available to the plants?
  • The amount of light a plant receives during a photoperiod?

What are PPF, PPFD, DLI, and Moles?

Photosynthetic Photon Flux (PPF)

Photosynthetic Photon Flux or PPF measures the total light produced by a light source per second. Another way to think of it would be that PPF is the amount of PAR that was emitted by your light source in a second. This measurement is measured in micromoles per second, more about micromoles coming up shortly. It is important to note the PPF measures the light created by your source but doesn’t reflect the amount of light that reaches your plant.

Photosynthetic Photon Flux Density (PPFD)

The second measurement of LED grow lights is PPFD which stands for Photosynthetic Photon Flux Density. This just means that it is a measurement of how much light per second reaches your plant’s surfaces, more technically it is the number of photosynthetically active photons reaching the surfaces of your plant. PPFD measures a spot in a specific location of your plant’s canopy. Its measurement is called micromoles per square meter per second. It can be shown in a mathematical express as μmol/m2/s.

Daily Light Integral (DLI)

The last measurement is DLI or the daily Light Integral. This measures the amount of light that reaches a plant in a day (or Photoperiod). An easy way to think of it is a day’s dose of required light for your plant. Technically speaking DLI is a measurement of the cumulative number of photons that reach your plant in a photoperiod. DLI is expressed as mol/m2/d which is the number of moles per square meter per day.

Moles Huh?

There are almost infinite numbers of photons (light particles) in visible light. The quantity is so large that is can’t easily be expressed in numbers. Things go off the rails as far as needing to understand this next part. A mole, is equal to 602,214,150,000,000,000,000,000 which isn’t a very manageable number to be working with. Instead, the measurement micromole is introduced which is 1 millionth of a mole. So, a micromole of photons would be one-millionth of 602 quadrillions. ACK!


  • PPF explains the number of photons of light are created by a light source each second
  • PPFD explains how densely your fixture distributes light photons on a square meter target area in one second.
  • DLI explains the number of photons that were delivered in a 1-meter square of space during a photoperiod (one day).


An Easier way to think about this

Use your imagination for a minute and think about things like this:

The light fixture is a cloud and the light falling from the fixture is rain falling every second. PPF, in this case, would tell you the number of raindrops falling from the cloud every second.

Think of light as rain and the light fixture as a cloud.

PPF tells us how many raindrops are falling from a cloud every second. Now pretend that the cloud produces 1 million raindrops per second. If those million raindrops fell from a big cloud the size of a State, you wouldn’t even be able to notice the raindrops. That same million raindrops per second in a tiny cloud the size of a house there would be a flood below the cloud. The raindrop density (PPFD) of the house-sized cloud would be much higher than from a cloud the size of a state.

If PPF tells us how many photons are being produced per second, then PPFD would be the number of photons that are landing on your plant ever second. The more light that hits your plant the more photosynthesis that can take place which leads to more growth of your plant.


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