Apr 12, 2019

3 Lighting Measurements to Improve Your Grow

Can Grow Lights Be Too Strong?

When it comes to the lighting you use for your plants, how much is too much? Believe it or not, there is a science behind finding out how many lights you should have and how to place them. It isn’t about just putting your one plant under an incandescent bulb in your bedroom closet anymore. The research is constantly evolving in an attempt to mimic the sun- both its intensity and spectrum. Don’t miss what our Grow Guru from The Dude Grows Show had to say about his experience with the different lighting technology. Learn how you can best use the newest lighting technology to your benefit to get the most out of your plants.

Lighting Spectrum

Lighting is one of the most important elements of your grow. Understanding how lights affect your plants allows you to use knowledge as power. The quality of the light provided is defined by the spectrum of light that they emit. This light allows them to conduct biological processes, such as growth and photosynthesis. Different ends of the light spectrum affect the plant differently, signaling to your plants to move from a vegetative stage to a flowering stage.

Color light spectrum chart

Every color of the rainbow within the PAR spectrum affects your plants. However, red and blue spectrums have the most influence on your plants’ growth and production. Red light is absorbed by the phytochrome receptor which increases the plant’s production of the hormone meta-topolin. Meta-Topolin helps to prevent the breakdown of chlorophyll in your plants and enables them to be green in color. Blue light is absorbed by the cryptochrome receptor and slows the production of the hormone auxin. Auxin is what helps with the vertical growth and the root development in your plants. Using a full spectrum light (a light that has all the colors of the rainbow emitting from it) is the closest way to mimic the sun.

After all this talk about spectrum, it is important to note that the color spectrum is the first thing that depreciates in a bulb. Don’t wait too long to change your bulbs or the spectrum’s degradation will negatively affect plant growth long before the lumens or PAR drop.

3 Lighting Measurements to Improve Your Grow

1 . PAR (Photosynthetically Active Radiation)

PAR is the range of light that is emitted from the bulb that is measured within the range of 400-700 nanometers (nm) but confusingly enough is not a measurement unit in itself. It serves as a point of reference to show if a light is within the spectrum to trigger the photosynthesis in your plants. If the light that you use is too far-red or ultra-violet (outside the 400-700nm), it can create adverse effects on your plants such as stunted growth or heat burn. You want to be sure that all of your plants are receiving a consistent spectrum.

2. PPFD (Photosynthetic Photon Flux Density)

The PPF is the most important thing to consider when determining how many lights are needed in your grow space. The PPF is the bulb’s “horsepower”. It is the mathematical number of photons per second that are coming out of the light at the point of source per second. This measurement is the way that you can ensure that your plants are receiving the light that they need to thrive.

It is important to note that there are planes of PPFD. PPF is the amount of light being emitted by the source and the density (the PPFD) is the amount of light in a certain spot of the room. The PPFD pertains to the plants directly under the light source. There are varying planes of PPFD as you move further away from the light. It is like a flashlight in complete darkness. The closer to the source the higher the density of light, as you move away from the light the intensity diminishes but the area of coverage increases.

3. CRI (Color Rendering Index)

Another rating to take into consideration when purchasing bulbs for your grow is the color rendering index. The CRI is the uniformity of the light spectrum in the PAR range and how even the light spectrum is. The sun is 100 CRI because it is completely even spectra. When purchasing a full spectrum bulb the CRI should be rated very high but some bulbs test higher than others. For example, light-emitting ceramics are very even and broad, running a high CRI, while HPS tends to run quite low.

What you are looking for is a relative Quantum Efficiency Curve, also known as the McCree curve. As previously mentioned, your plants benefit from exposure to different color spectrums during different stages of growth. You want to ensure that your plants are capable of going through their photosynthetic processes (natural biological growth process) by providing the adequate amount of spectrum needed at the correct time in their grow cycle.

Knowing Your Grow Lights

Plants are products of photo-tropism that determine their growth by exposure to different wavelengths of spectra. By withholding the blue spectrum during times of vegetative growth you will end up with spindly twizzler-looking plants. When a plant is denied the red spectrum during the flowering stage, you find yourself working with bushy little shrub plants. This is why an even spectrum is so important.

If your grow has areas that are prone to more shadows you may experience your plants growing at a slant to move towards the point of the light source. The reason is that auxins in the plants cause movement away from the shadows and elongation of cells on that side so that the plant bends to face the light. With that being said, there is such a thing as too little light in your grow room. Too little light exposure, in general, will not allow your plants one of the most important elements that it needs to generate their food and grow.

The amount of light exposure, or photo-periodicity, is also important. Photo-periodicity is how a plant knows when to enter the flowering stage depending on the number of darkness hours that it experiences. When plants are in a natural outdoor environment, they know when to enter the flowering stage due to the lessening of daylight hours that occur in the fall season. Indoors, you mimic this change in season by changing the number of hours they are exposed to the grow lights (or are in darkness).

Grow Light Bulbs

You need to take into account many factors when considering what types of bulbs to use in your grow. This includes the size of your grow, how much you want to invest in your grow, and the number of plants that you plan to have. We were lucky enough to spend some time with our Grow Guru to pick his brain about the different lighting options currently on the market.

High-Pressure Sodium (HPS) Grow Lights

High pressure sodium hydroponic grow light

Typically, HPS lights are recommended to be hung at least three feet above your plants. You can place HPS bulbs in either an open fixture with a powerful air conditioning unit or air-cool them. Air-cooled HPS can be hung 18-24 inches above your canopy. HPS bulbs are offered in 600-watt and 1000-watt bulbs. A 600-watt HPS will cover a 3×3 to a 4×4 grow space and will put off less heat than a 1000 watt. A 600 watt should be placed about 16” from your canopy and a 1000 watt should be about 20” away. A 600 watt is a few extra dollars than a 1000 watt but is more energy-efficient, giving you more light with less electricity. The Grow Guru suggests HPS bulbs for flowering but insists they are not great for the veg stage due to the lack of blue in their spectrum.

Luxx DE 1000w HPS Fixture

Luxx DE 1000w HPS lighting fixture

The Luxx Lighting 1000w DE HPS fixture is the result of thousands of harvests, decades of cultivation experience, and passion for the garden. Every component of the DE 1000w was purpose-designed and built from the slim-line reflector to the low profile ballast, this fixture was designed with the grower in mind. For the past decade, growers have been utilizing greenhouse fixtures indoors. The DE 1000w is the new standard for indoor cultivation. By growers, for growers. The price may be a bit steep but it is well worth the investment..

Fluorescent Grow Lights

Seedlings in indoor hydroponic garden under fluorescent grow lights

Fluorescent bulbs are “white light tailored spectrums”. The Grow Guru finds their canopy penetration leaves something to be desired. A positive to this is that they emit very little heat. The PPF is low, and therefore does not penetrate the canopy as desired or as well as other lights with a higher “horsepower”. This is not to say that you can’t produce a quality product with fluorescent, in your vegetative stage at least, and are recommended for a beginner grower due to their low cost. We do not recommend attempting to use these for flower. You will not be happy with your results. It is recommended to keep your fluorescent bulbs 12 to 18 inches from your canopy to avoid potential heat stress. You can always do the “hand test” and hold your hand at the level of the canopy for 30 seconds and see if your hand can stand the heat. You’ll want to raise your lights if you can’t stand the heat.

LED Grow Lights

Iceberg lettuce growing under LED lights in hydroponic garden

LEDs emit white light and can be placed directly over the canopy to the point that plants can grow into them. This can be helpful for growing in tight quarters.

Your plants may experience a bit of bleaching on the tips of the leaves due to overexposure to light and arresting the production of chlorophyll. The bulbs don’t emit heat down to the plants, but instead, create heat sinks that exit out the back of the light. The prices of LED are higher than some of the other bulb options on the market but the Grow Guru believes we will see prices drop as the technology advances.

Ceramic Metal Halide (CMH)/Light Emitting Ceramic (LEC) Grow Lights

The Grow Guru lists CMH as the industry’s “bulb winner”. The price is right for the quality that you’re getting out of the bulb. Also, it has a high CRI rating making it almost as good as growing under natural sunlight. There are both 91 CRI bulbs and 99 CRI bulbs. CMH are white light bulbs and are typically best for larger grow rooms. CMH cannot be air-cooled, but since they put off far less heat this is not usually a problem for most growers. Make sure you place them at least 18 inches away from your canopy.

CMH does allow you to see the true colors of your budding babies without the aid of light filtering glasses, although we don’t suggest doing it for any length of time without them. Protecting your eyes against these powerful bulbs is important. Keep your eyes open for our article coming soon on proper eye protection. You don’t want to grow blind!

For more on CMH lighting technology check out LEC 315: Ceramic Metal Halide Technology.

Hang Your Grow Lights

The placement of your lighting technology not only affects how the canopy receives light but also delivers heat to your plants as a byproduct. Placement of your lights is a total science and can be calculated with all the information given to you on your bulb’s box. Each bulb has a recommended distance they should be placed from your plants to avoid heat stress. Make sure to follow the recommendations of the manufacturer to get the most out of your plants.

The More You Know the Better You Grow!

Integrating your lighting system into your overall grow design before building your room is always recommended when starting from scratch. Whether you are designing a warehouse or looking to improve your current grow setup you can benefit from the following pro tips:

  • Ensure that your lighting provides consistent coverage across the canopy of your crop.
  • Do not assume that your plants are receiving enough light. Use the tools available that you have available such as a PAR meter. They enable you to measure the energy coming from your bulbs.
  • Provide your plants with a full spectrum of PAR to ensure you receive the best product from your plants.
  • Just like watering, you can over-saturate or under-saturate your plants with light. Set timers to make sure your plants are getting an adequate amount.
  • Maintain the quality of your bulbs and plan on replacing them at the appropriate intervals.
    • HPS bulbs – 9-10 months
    • DE HPS Bulbs – 10-11 months
    • CMH/MH bulbs – 6-8 months
    • Fluorescent bulbs -8-9 months
  • Make sure to place your lights at an appropriate distance from your canopy to avoid heat stress.