Whether you are buying LEDs for the first time or upgrading your current system, the LED grow light industry can feel a bit like the wild, wild, west.
Most of the terminology has been adapted from older technologies such as HPS or MH. It is not always useful for describing the intensity, efficiency, or usability of an LED grow light.
As you wade into the crowded LED grow light arena, use this Complete Buyers Guide to navigate the options. The following questions should help you under stand what functions and measurements are both useful and applicable for LED grow lights, specifically for growing cannabis indoors.
LIGHT-EMITTING DIODE (LED)A small semi-conductor that produces light when electricity flows through it.
WHAT IS YOUR TOTAL BUDGET FOR LIGHTS?
Lighting is one of the few areas of an indoor grow room where it pays to invest in high quality, long-lasting fixtures. Yet the price is not always a clear indicator of LED quality.
Look at the entire package (intensity, spectrum, brand name, etc. ) to determine if the fixture is appropriate for your space. Smaller units from trusted brands are now available for under $200. Larger LED grow lights, suitable for larger footprints or commercial operations, usually begin at $500 but can easily go over $1000 per unit.
If budget is your main concern, start looking at LED grow light options using price point as the first filtering factor.
WHAT IS THE LIGHT INTENSITY OF THE FIXTURE?
LEDs should advertise total light intensity (PPF) plus the light intensity as it diffuses away from the center (PPFD). This is the total light intensity, versus the usable light intensity. Check the PAR map for the fixture to understand the PPFD diffusion rate.
Studies have determined the ideal PPFD for growing cannabis can vary depending on stage. Use the following as a guide:
- Seedling 100-300 μmol/s
- Clone 75- 150 μmol/s
- Vegetative 300-600 μmol/s
- Bloom 600+ μmol/s 
PHOTOSYNTHETIC PHOTON FLUX (PPF)The number of photons per second put out by a light source or how much PAR the fixture produces.
PHOTOSYNTHETIC PHOTON FLUX DENSITY (PPFD)The number of photons per second put off by a light source in a defined area.
HOW MUCH TOTAL PPF DOES THE LED LIGHT IDEALLY NEED TO PRODUCE?
- 5’ x 5’ space requires 1500+ μmol/s
- 4' x 4' space requires 1 100- 1500 μmol/s
- 3'x 3' space requires 600-850 μmol/s
- 2'x 2' space requires 275-375 μmol/s
μmol/sThis is a standard unit of measurement for light, called micromoles.
PHOTOSYNTHETIC ACTIVE RADIATION (PAR)The amount of light produced by a fixture which is usable to plants.
WHAT TYPE OF DIODES DOES THE FIXTURE HAVE?
Single-wavelength (or 'mono') diodes: These are early model LED grow lights, which are quickly getting replaced with more efficient and powerful diode advances. They are affordable but have lower PPFD and worse canopy penetration than the newer alternatives.
Full-spectrum white didoes: These provide better intensity, efficiency, and canopy penetration. Increasingly chosen as the best choice by growers, provided it fits the budget.
DOES THE PAR MAP INDICATE SPOTLIGHT STYLE OR EVEN DISTRIBUTION ACROSS THE CANOPY?
A fixture's PAR map tells you if the light intensity or PPF is focused in roughly a small area or if it's relatively consistent across the entire map. Better lights will provide more even PPF readings from one side to the other.
Enhanced LEDs: These fixtures come with full-spectrum white diodes with added blue, red, or UV options to improve growth. Some brands are adjustable to switch between a more robust blue spectrum to a stronger red spectrum as you move between the plant's growth stages.
DO YOU NEED LED GROW LIGHTS SUITABLE FOR VEG, FLOWER, OR GENERALLY APPLICABLE TO BOTH GROWTH STAGES?
Ideally cannabis requires two slightly different light spectrums for the veg and flower stages, mimicking the natural changes of the seasons. Are you looking for a light that will cover both stages or a fixture to enhance a specific stage?
WHEN ARE COBS APPROPRIATE?
In certain grow rooms , a COB may be appropriate as the sole light source or as a supplemental one. They deliver greater uniformity and light intensity than conventional LED fixtures, but the beam of light is much more focused. COBs are compact with low heat production.
They make excellent supplemental fixtures, as they can only provide a single spectrum of light (blue, red, UV, etc.). 
HOW MUCH ELECTRICITY DOES THE FIXTURE USE IN WATTS?
One of the big advantages of LED grow lights is their energy efficiency. Most fixtures are between 30 to 50 percent more efficient than conventional HPS lights.
Each brand and style will draws lightly different wattage. Using the price per kilowatt-hours noted on your local power bill, you can determine roughly how much the LED grow light will cost to run per hour.
WHAT IS THE VOLTAGE RATING?
The USA and Canada use a standard 120v. However, other countries vary. In the EU, they use a 230v. Confirm the LED grow light you are purchasing uses the necessary voltage.
WHAT IS YOUR EXPECTED CANOPY SIZE IN SQUARE FEET?
The maximum coverage for most growlights affordable for the small - scale grower i s 5' x 5'. Many growers use one or more lights within the same grow room to provide adequate coverage over the total canopy.
WHAT IS THE UNIFORMITY AND INTENSITY OF THE LED GROWING LIGHT ACROSS THE FOOTPRINT? (HINT LOOK AT THE PAR MAP).
Not all LED grow lights were created equal. Don't just trust the brand's coverage claim. The numbers on a PAR map can vary significantly from the central focus towards the edges.
If you want to get the most out of your light, look for a PAR map with even distribution from one side to the other. Generally, these fixtures may be more expensive. If the light you are buying has poor distribution, calculate coverage area based on the actual useable square footage.
DO YOU WANT OR NEED ADDITIONAL LENSES?
With smaller diodes, some growers prefer to intensify the light with TIR lenses (glass lenses).
These are useful to increase the intensity of the diodes but will lower the total overall footprint of the light.
In certain circumstances, they may be useful as a means to narrow the focus of the light and improve otherwise wasted dispersion.
TOTAL INTERNAL REFLECTION (TIR)A lens used to change the direction or intensity of the normal diode.
WHAT ARE THE PHYSICAL RESTRICTIONS FOR THE SIZE AND WEIGHT OF YOUR LED GROW LIGHT?
Realistically, what size grow light is suitable for your space? There are several considerations, including:
- Weight restrictions for hanging from the ceiling or support system.
- Spacing between the canopy and LEDs during all stages of the plant's growth.
- Physical width and length of the fixture.
- HVAC considerations for small spaces.
WHAT ARE THE LEGALLY REQUIRED CERTIFICATIONS AND/OR MARKINGS?
Commercial growers in the US must use either a UL or ETL certified fixture in their grow rooms. Home growers do not legally require any special markings. However, you want to rely on these certifications as a means to confirm product safety and quality. Internationally, there are similar certifications, such as CSA (European Union) and CE (Canada).
DOES IT COME WITH A STANDARD WARRANTY?
How long is the warranty, and what is included in the manufacturers or distributors' fine print? Trusted LED grow light brands (Growers Choice, Electric Sky, Timber Grow, Kind LED, and HLG are some examples) have a three-year warranty policy.
DOES THE LIGHT FIXTURE COME WITH SPECIAL FEATURES OR ADD ON DEVICES SUCH AS CONTROLLER, SCHEDULER, DIMMER, SUNRISE/SUNSET, SPECTRUM CONTROL?
Some grow lights have special ty features making indoor growing easier or more beneficial for plant health. For example, some lights have a built-in sunrise and sunset feature to gradually turn lights on or off according to the timer.
Other lights allow for precise spectrum control , to adjust for blue during vegetative stage or reds during flowering.