Reeferman Genetics – Chapter 7 – Grow Top Shelf Buds

Chapter 7 of our 14 part weekly series will talk about the importance of lighting. Follow step by step to grow top shelf harvests like a pro. The information and instructions are highly scalable. These proven and well developed methods and technologies will work for anyone. Whether you want to grow some personal crops of buds at home or if you intend to fill a warehouse.

Lighting Choices

Grow Lighting choicesLike nutrients, there are a lot of choices and claims when it comes to what is “the best grow light”. This book is not out to debate anything, we will make recommendations based on what we know works well and in harmony with the other technologies we discuss in detail. You might do better sourcing and installing a different type or style of lighting; however, you can most certainly do worse for your crop and your bank account.


We have already mentioned we prefer high output LED (light emitting diodes) grow fixtures over other lighting sources like HIDs (high intensity discharge) including High Pressure Sodium, Metal Halide and Ceramic Metal Halide. To recap very briefly, we choose LED because:

-safety; cooler operating fixtures and lower wattages

-efficiency; higher rates of light for photosynthesis for every watt of lighting power consumed

-closer to canopy tolerances; LED fixtures will not burn foliage and buds when operating at close distances to the tops of plants, ideal for getting the most yields out of tight spaces

-even coverage; good LED light fixtures spread intense light out over a wider area versus HID sources that emanate from a single point

-tailored spectrum; light quality is much higher; combinations of individual diodes can be tailored for a specific output versus over amplified and lesser quality light from HID sources

-faster flowering cycles; buds mature faster, up to 25% less time in budding to reach full maturity.

-no lamps to replace or switch; this saves big on money over a few years because LED diodes and drivers last a long time.

-fewer hassles with mites or mildew; it is true, ask around, side by side in the same environment there will be fewer pests or problems on LED grown cannabis plants versus the same strain from the same batch grown under HPS lighting.

The bottom line from choosing high quality LED crop lighting over other sources is harvesting great yields of super high quality tight buds that came with fewer hassles and less power. While it depends on the strain naturally, harvesting 450 grams of top shelf bud from 640 watts of LED grow lighting in 6 weeks is not uncommon, some exceptional growers with the right strain may exceed this benchmark considerably.

Choosing the Right LED Grow Light

Note: for propagation of small cuttings and seedlings we still prefer T-5 fluorescent lighting

There are lots of LED fixtures to choose from. In our growing model, we finish plants in a 3’ X 6’ horticultural tray (outside dimensions are slightly larger) and establish and veg our plants in a 2’ x 4’ horticultural tray. The tray dimensions we use give us our required lighting footprint, i.e., how much area we need to cover with evenly distributed intense grow lighting.

Pre-Veg and Veg

LED Grow LightsA 240 to 360 watt Quantum Board (QB) LED grow light gives us more than adequate coverage for our 2’ x 4’ veg tray. LED lighting strips, i.e., a “spider” will also work well. Either a Quantum Board or Strip style LED lighting at the recommended wattage is equally good at supporting two to four large plants that can serve as mother plants. For every 3’ x 6’ horticultural tray you intend to have in your flowering room, count on needing at least one 2’ x 4 ‘vegetative LED set up to always keep the flowering room productive. This serves to help avoid down times because there are no good sized plants available to replace the ones you may have recently harvested.


Note it is wise to maintain separate vegetative and flowering rooms. Besides the ability to keep your gardens at maximum production levels, the two different rooms have different needs. A larger room with a more intensive environment used for flowering plants is not ideal for raising smaller young plants, it tends to stress them.

So, if you intend to keep some mother plants (for cuttings) selected from your favorite seed crops and keep a fresh crop of veg plants to replace harvested flowering plants on the ready, budget for two 240 to 360 watt Quantum Boards or Strips (Spiders) in veg for each 3’ x 6’ horticultural tray in your flowering room.

A dimmer switch is recommended for all LED lighting in veg. Full power on new plants is not only a waste of electricity, but it will also stress young plants and hurt growth. Gradually ramp up lighting levels as recommended in the guide given further into this section.

A good spectrum rating for your veg LEDs is from 3500 to 5000 K (kelvins). A small bandwidth of Red, Far Red and UV can be beneficial but is not altogether necessary for veg. 3500Kelvin fixtures are also suitable for budding plants, the higher the Kelvin rating, the “bluer” the light is. A lower Kelvin means “redder”, which promotes flower development and maturation.


For flowering and budding, 600 to 800 watts of full spectrum (with Red, Far Red, and optionally UV) LED grow lighting is recommended for each square meter. So, that is two fixtures for each 3’ X 6’ horticultural tray. Quantum Boards are good here while Spiders (groups of strips) help to promote more even coverage. Spider type LED grow light fixtures may also allow you to adjust the position of each LED light bar within the fixture, helping you to better even out light intensity from the center of the fixture to the edges. Newer models are “foldable” for smaller sized package in shipping and to save time, i.e., no assembly required, ready to plug in out of the box.

LED Grow Light Pricing & Sourcing

A high quality professional LED grow light fixture is not cheap to buy. Expect to pay from 200-300 dollars for smaller wattage quantum boards, and from 600-1600 dollars for higher wattage board or strip fixtures. You most often get what you pay for, however, it can also pay to shop around, there are plenty of social media chat boards and sites filled with real growers who are happy to share their findings with a particular LED grow fixture. Take with a grain of salt, however, as “everyone’s an expert” and there are also fake accounts directed by salespeople looking to sell their own brand and diminish the esteem of others.

LED Grow Light Technical Stuff, the Basics

LED Light StripsYou will hear a lot of different terms, theories, and jargon when people discuss LED grow lights. So, here is some basics to familiarize yourself with first.

Diodes or Chips-the small individual “lights” arranged in the LED fixture.

Driver-the heavier piece in the fixture that regulates electrical current to drive the LED chips.

Heat Sink-the metal piece that boards with the chips or diodes are affixed to that helps dissipate heat away from the LED lights. Sometimes this is passive (no fan) or may also be active (with fan)

Light Board-i.e., Quantum Board or Strip, the piece that connects the LED chips or diodes to the electrical current, typically mounted to a heat sink.

Dimmer-just like it sounds, used to dial the lighting intensity up or down, typically in a range of 30 to 100%. Some are a simple screw turn or knob. Others may have a digital interface or even operate from your smart phone.

Additional Notes on LED Basics

Higher quality fixtures have a protective covering over the board or strips. This may be polycarbonate, glass, or an applied polymer coating. If your diodes are unprotected, they may pose a hazard or become damaged if contacted with moisture, i.e., plant sprays.

High quality LED fixtures have some weight to them, be prepared to support it with heavy duty light hangers or chains from secure hooks or tracks mounted into studs. The diodes and drivers do not have much weight to them, it is the metal (usually aluminum) that accounts for most of the weight. The more metal, the better the fixture dissipates heat away. You want to make sure it is easy to adjust fixture height as necessary from the top of the crop. Most LED fixtures operate best from ten to eighteen inches above the canopy.

Measuring LED Grow Light Intensity

Measuring LED Grow Light IntensityPAR meters measure and give readings as (µmol m-2  s-1) aka micromoles per meter square per second. These are a little more expensive to buy and source versus traditional light meters which measure in Lux, Lumens or Foot Candles.

To keep things simple and brief, neither is perfect for measuring LED grow light values, believe it or not, you can trick a high end PAR meter into thinking a flashlight is better than natural sunlight at noon.

However, a PAR meter does provide a point of reference, as does as Lumens or Lux meter to help make your results repeatable and to give you a relative value. The readings will be specific to your grow light spectrum when it comes to LED grow light values Other sources like HPS, MH, CMH will have some variation from lamp to lamp although not nearly as wide as the differences between LED fixtures from different manufacturers. All this has to do with how the spectral output of LED is tuned or balanced.

Most high end LED fixtures are going to be in the 3000-4000K diode range with added Red and Far Red. Some will also add a small bandwidth of UV. The values given in our recommended LED light intensity chart is somewhat transferable from one fixture to another. Just do not take it as an absolute, rather, as a baseline or point of reference to start with.

Recommended LED Grow Lighting Intensity Values

Germination, Rooting Cuttings, PreVeg*

Cannabis roots LED LightingWe recommend using T-5 or similar full spectrum fluorescent lighting for establishing small transplants. It is affordable and works very well when plants are small.

80 to 120 µmol m-2 s-1 is typically adequate. Vegetative Growth

Full spectrum LED with a Kelvin rating of 3500-5000K is ideal here.

200 to 450 µmol m-2  s-1 will encourage rapid early root and shoot development while keeping plants compact and sturdy, too strong will stress plants, too little will stimulate weak stretchy growth patterns. Added UV light may promote stretching, some strains respond well to added UV in veg while others do not.

Early Flowering

Full spectrum LED with a Kelvin rating of 3000-3500K is ideal here. Added UV light may be beneficial, especially with strains that maintain tighter growth patterns in early flowering and transitional development.

800-1200 µmol m-2  s-1 will stimulate rapid development and lots of new budding sites. The greater a jump in healthy and sturdy development you create here the less time that is required in vegetative growth earlier on.

Flowering & Peak Budding

LED Grow LightAs above, however, with increased intensity. If using a tunable spectrum, this is the time to increase light levels in the Red bandwidth. UV light is also beneficial for crop quality and bud density.

1200-1600 µmol m-2 s-1 Ripening.

Some growers reduce light intensity and grow room temperatures in the final days before anticipated harvest. This is said to improve colorations, aromas, and flavors. For faster harvests and maximum bud weight, we recommend maintaining high light intensity and moderate grow room temperatures. UV light at this stage will often increase essential oil production and potential potency.

1200-1600 µmol m-2  s-1   OR 600-800 µmol m-2  s-1




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