LED grow light efficiency in umol/Joule (400-700nm) is often stated as micromole per Joule -- or seen as umol/j or PPF/W--means for every joule of electrical energy (Joule = watt x second) a number of photon micromoles are produced. Most entry-level LEDs are between 1.0 and 1.7 umol/j. Higher end LEDs are usually 2.0 umol/j. 400-700nm relates to the wavelengths of light in nanometers (nm). 400-700nm is the spectral range that plants use most efficiently to photosynthesize. This range is also often referred to as the range of Photosynthetically Active Radiation (PAR).
LED grow lights can be designed with spectra (plural for spectrum) in many different recipes, as they're called. When thinking about buying a LED grow light it's important to think about what phase you're going to use the grow light for propagation, vegetative growth, flowering phase, or a generalist for all phases of growth, often referred to as 'full spectrum' or 'full cycle.'
Often you will see spectral charts showing what looks like a rainbow of colors on a graph with numbers below it. The numbers below are known as nanometers or thousandth of a meter long. Light waves have changing wave frequencies that cause us to see different colors. Plants have evolved to use mainly blue and yellow to red light spectra to photosynthesize, although they do use other colors including infrared, green, white and ultraviolet. See the chart below to see an example of a LED spectral chart:
To get you more familiar with LED grow light spectral charts for different phases of growth, below we have the HLG 300L Rspec (flowering phase/full cycle) and Bspec (vegetative phase) so you can compare them. Notice how the HLG 300L Rspec has more relative intensity in the yellow, orange, red area and a little less in the blue.
The HLG 300L Rspec has been designed to focus on the flowering phase, although still has ample blues to use in vegetative growth if desired. See how the HLG 300L Bspec has relatively more intensity in the blues than the Rspec, but still has good intensity in the reds. HLG, like many other LED companies, makes one vegetative focused light and one flowering/full-cycle light. You'll see other companies do the same when they have two models instead of just one generalist model.
Wattage is commonly used to reference LED fixture size, price and coverage area. While wattage is a good guildline, it isn't the most accurate way to determine the coverage area of a LED grow light. The most accurate way to measure a lights output is in PPFD (photosynthetic photon flux density AKA umol/j/m2). PPFD can be more simply thought of as the number of light particles (photons) that fall on a given surface each second.
PPFD (umol/j/m2) and DLI is the correct metric for measuring useful light intensity over a given area. Coupled with the correct spectrum for your plant type and phase of growth, PPFD (and spectrum) are the keys to a successful grow. However, for the purpose of estimation, we will report wattage calculations in this article.
When we talk about wattage inthis article, we are referring to the wattage drawn at the wall, not what the manufacturer states as "LED wattage" - which is typically the product of the maximum LED wattage and the number of LEDs. For example, 300 x 3-watt diodes would be a 900 watt LED grow light. However, the LED grow light might only draw 500 watts at the wall.
When shopping for a LED grow light, it's important to take these considerations into your purchasing decision:
What is the length of the warranty of the LED light?
Most LED grow lights last around 50,000 hours. This usually equates to about 5 years of solid use. If you find an LED grow light that has a 1 or 2 year warranty, then assume it is made with the least expensive LED components available and don't expect it to last longer than the warranty period. Most reputable companies will have a 3-5 year warranty for the LED lights.
If a diode goes out, what is the process to get the fixture repaired or replaced?
This is an important consideration for your growing operation. Ask yourself, "If my LED light goes out, do I have a substitute light I can use if I need to send my LED light in for repair or replacement?" If the answer to that question is no, you may want to look for fixtures that have modular aspects to them where part of the fixture can be disassembled and repaired/replaced while you can continue to use the remainder of the LED grow fixture. Some examples of modular fixtures are:
Does the LED light have a good way to dissipate heat away from the LED diodes?
One of the aspects that makes LEDs degrade and fail is heat. If LED diodes don't have a good way to 'exhaust' the heat they produce, then they operate less efficiently and they become less reliable. This is a double whammy that you want to stay away from. When shopping for LED grow lights, look for ones that mention a thermal heat management design, spaced out diodes, underdriving the wattage of the diodes, and heat sinks. We've shown some images below of good examples of LED lights with heat dissipation design and ones with bad heat dissipation design.
We're doing something no one has ever done before -- well, sort of. Each LED company who takes their craft seriously focuses on buying high quality components that will last a long time (read: not fail within 2 years) and have high efficiency/output ratings. To test LED grow lights comprehensively, you really need to send them to a laboratory that will will run the light through a battery of instrumentation. Each test from these companies is not cheap. For all the testing that we're requesting, the bill can run up to about $1,500 per light. This was no cheap endeavor, but we wanted to create the most unbiased, comprehensive, and informative comparison review test on the web. Therefore we needed to be using the best equipment available to do our testing.
This is not your normal 5' x 5' grid where you use a lumen meter. That can be somewhat helpful, but we're going to use testing done at UL and Light Laboratory Inc., which are independent 3rd party light laboratories that do not have an incentive to make one brand look better than another. These are the same laboratories that most LED manufacturers use to test when designing their lights.
Each test from these companies is not cheap. For all the testing that we're requesting, the bill can run up to about $1,500 per light. This was no cheap endeavor, but we wanted to create the most unbiased, comprehensive, and informative comparison review test on the web. Therefore we needed to be using the best equipment available to do our testing.
The other amazing thing about this test? It's never-ending. That's right, we're going to continually test lights and add the information to this page along with the PDF of results directly from the testing lab. We'll also include information in easy to digest tables and graphs below, along with definitions of the terms so you won't need to be a optical scientist to understand what's going on.
There is no one size fits all when it comes to LEDs. We hope this testing helps you choose the best light for you. Also, if you're going to purchase a LED grow light soon, please consider buying from GrowersHouse.com. We put a lot of time and money into this testing to help our customers make informed purchasing decisions. Being a customer helps support our mission of educating fellow growers.
To make it easier on our customer's wallets, we're also offering a 5% coupon good for any of the lights featured in the testing below: GHLED5. Not combinable with other sales or discounts.
Definitions of headings are below the table.
Efficiency (umol/Joule) [400-700nm]
Total PPF (400-700nm)
Luminous Efficacy (lm/W)
Brand of LED chips
California Light Works GH PRO 340
HLG 550 V2 R-Spec
California Light Works Solar Storm 550
Gavita Pro 1700e LED
Fluence SPYDR 2p LED
Fluence SPYDR 2i LED
HLG 650R LED
LED Efficiency in umol/Joule (400-700nm): Often stated as micromole per Joule -- or seen as umol/j or PPF/W--means for every joule of electrical energy (Joule = watt x second) a number of photon micromoles are produced. Most entry level LEDs are between 1.0 and 1.7 umol/j. Higher end LEDs are usually 2.0 umol/j. 400-700nm relates to the wavelengths of light in nanometers (nm). 400-700nm is the spectral range that plants use most efficiently to photosynthesize. This range is also offtenly referred to as the range of Photosynthetically Active Radiation (PAR).
Total PPF (400m-700nm): PPF is the abbreviation for "photosynthetic photon flux". It gives the information on the number of photons, which are emitted by a light source. Only photons in the wavelength range from 400nm to 700nm are considered. This is the so-called PAR (photosynthetic active radiation) and photons within these wavelengths contribute to photosynthesis. The unit of the PPF value is µmol/s (quantity of light particles emitted per second). Knowing the PPF value from different light sources allows an easy and objective comparison on the total light output which can in theory contribute to photosynthesis. Please note that the PPF does not consider the direction in which the light is emitted.
Luminous Efficacy (lm/W): A measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt. Wavelengths of light outside of the visible spectrum are not included in this measure. The majority of the light plants use to photosynthesize are visible, but there are non-visible spectra that plants also use including ultraviolet and infrared.