PAR stands for photosynthetically active radiation. It designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis. LEDs attempt to tailor the spectrum to the plant that is being cultivated. The spectrum visible to the human eye is about 380 to 740.

Lumens is a measurement of the total quantity of light that is visible to the human eye.

PPF stands for photosynthetic photon flux. It’s a metric that indicates the amount of PAR produced by a lighting system each second. It is expressed as micromoles per second (μmol/s).

PPFD stands for photosynthetic photon flux density, and measures the amount of PAR that actually arrives at the plant or the number of photosynthetically active photons that fall on a given surface each second. It is a measurement of micromoles per square meter per second (μmol/m2/s) onto the canopy. Widely available handheld PAR meters are used to measure PPFD.

When evaluating the proper amount of PPFD, the grower should take an average measurement of not only the area below the light, but the entire area, because light from one fixture will spill over into the surrounding areas. Also, when evaluating this metric the distance over the canopy should factor into the equation. A manufacturer can skew the metrics in a number of different ways. For example, one way is simply by raising or lowering the light. The final calculations that you should base your decision on are produced using a quality software package and Illumination Engineering Society (IES) files. The IES files are generated when a grow light is mounted in an integrating sphere. All testing should be performed by an independent third-party testing laboratory and certified to ensure accuracy.

he efficiency of a grow light can be simply calculated by taking the PPF and dividing it by the wattage. This becomes an important metric on larger operations where inefficiencies can be very costly. Although PPF does not tell you how much of the measured light actually lands on the plants, it is an important metric if you want to calculate how efficient a lighting system is at creating PAR. This formula is PPF/watts which indicated by micromoles per Joule of energy or µmol/J. In the case of our Verta-8 the PPF of 1589 is divided by the 649-watts or a factor of 2.45 µmol/J.

The exact light spectrum each plant requires continues to be an elusive construct. In other words, there is little agreement on lighting strategies during various plant growth stages. What we do know is that the blue light lends itself to the vegging portion of the life cycle of a plant while the red portion of the spectrum lends itself to the flowering portion of the cycle. Although the ratio of spectra colors is up for debate, and it’s questionable how much genetics factors into the equation, science is leaning toward a balanced approach of reds, blues, and greens while factoring in the crop and the region. Ultimately, we’re trying to simulate the sun and there is much we do not know.

LED technology is gaining the respect of today’s professional cultivators because it enables the grower to finely tune the spectrum to the plant. In contrast, older, more inefficient technologies such as High-Pressure Sodium, Metal Halide, and Ceramic Metal Halide bulbs don’t have that flexibility.

Although research indicates Ultraviolet Light (10nm~400nm) can be dangerous in larger doses, smaller amounts seem to contribute to the taste and smell. While this spectrum does not affect plant growth, studies indicate that the UVB spectrum can increase the THC content in Cannabis. Because this research remains somewhat speculative and can be dangerous, SpecGrade does not integrate this spectrum into our grow lights. Rather, we encourage our cultivators to cost-effectively add it by simply adding low cost PAR38 lamps throughout the grow facility and controlling them on a separate timer.

UV Light

The CMH spectrum also contains UV-A, UV-B, and UV-C. Because UV-C is harmful the glass envelope of a CMH will block that spectrum leaving only UV-A and UV-B. MH has no UV spectrum. Because this research remains somewhat speculative and can be dangerous, SpecGrade does not integrate this spectrum into our grow lights.

Blue Light (430nm~450nm) is typically encountered in nature at midday, when the angle of the sun is directly vertical or close to it. This spectrum is critical to a plant during the vegetative stage of life where terpene development occurs. In a commercial grow facility where every cubic foot must be productive, stretching must be minimized. Stretching is a survival mechanism to ensure the plant gets enough light or nutrients.

Also, SpecGrade’s thermal management design will guarantee that the plant will not be exposed to excessive heat stress at this early stage of life. Millions of years of plant evolution using the sun’s spectrum is ideal for vegetative growth. The red-blue light combination is strain and species-dependent. These spectra increase the photosynthesis rate, thereby increasing yields. Research also indicates increased amounts of blue light will induce flowering. However, research also indicates that blue light suppresses stem elongation resulting in shorter, more compact stems with thicker, denser leaves compared to plants grown without blue light. So we can maximize ROI by adding more blue to the spectrum. Our A1 spectrum (the single spectrum) was designed for the entire life cycle of a plant, based on the wide recommendations from botanists to use a balanced full-spectrum light source that includes high amounts of blue light.

Green Light (500nm~550nm) often does not get the attention it deserves when growers evaluate spectra. However, research indicates that green light drives photosynthesis by penetrating further into the leaf. Green light gets absorbed by the lower chloroplasts that increase leaf photosynthesis to a greater extent than red or blue light. For this reason, many cultivators have reported growing a greater number of Cannabis secondary buds than they were able to experience with a high-pressure sodium light source.

Red Light (640nm~680nm) is most prominent when the sun is low in the sky in the morning and evening. It stimulates high growth in a plant, but without the limiting effect of blue light which obscures the chloroplast to protect the plant from high-blue midday sun. Because of this, red light is very efficient at producing fast-growing, tall, and strong plants and consequently produces some of the most impressive height and stem width in plants. However, if plants are grown under only red spectrum lights, they can become thin and leggy.

Far Red Light (730nm) has a negative effect on seeds’ germination. And, research indicates that it has a significant effect on leaf size, stem length, and plant height. Because of these reasons, it should not be used in the early stages of a plant’s growth.

Every plant on earth has over 5 million years of DNA based on sunlight, which is, of course, full spectrum. Our grow light simulates the sun based on proven spectra and runs at a sustainable energy-efficient intensity. It’s designed to successfully augment the photosynthesis process for optimum plant from propagation to flowering.

There is a significant difference between Ceramic Metal Halide (CMH), Ceramic Metal Halide Double DE (CMH DE), and Metal Halide (MH). CMH bulbs are different than MH in that the CMH uses a ceramic tube and the MH uses a quartz tube. This allows the lamp to burn at a higher temperature which means a better mix of gasses, thereby making the CMH tube much closer to natural sunlight than either MH or High-Pressure Sodium (HPS) which makes it a superior choice for growing plants. However, it puts off a substantial amount of heat, which is undesirable. This is indicated by looking at the CRI (Color Rendering Index, see Figure 12). CMH has a CRI of about 92 (closer to full spectrum) verses MH with a CRI of 60 and HPS, with a CRI of 25.

The MH lamps are excellent at the flowering stage because they contain more blue spectra. However, they lack the warmer reddish/orangish spectra. HPS lamps are excellent light sources for vegging because they contain more of the reddish/orangish spectra, but they lack the cooler blue spectra. CMH lamps offer an advantage because they work well for the whole grow cycle because of their ability to mix gases. On the other hand, by mixing red and blue spectra LED chips we are able to tweak the overall spectrum to the strain of the plant.

The Color Rendering Index (CRI) is a scale from 0 to 100 (100 is the sun) indicating how accurate a given light source is at rendering color when compared to a reference light source. The higher the CRI, the better the color rendering ability. Light sources with a CRI of 85 to 90 are considered good at color rendering. The SpecGrade LED has a CRI of 92 making it an excellent full spectrum light source to grow with.

One of the biggest advantages of LED lighting is the massive energy savings. They offer up to 40% savings when compared 1:1 to high-intensity discharge (HID) lighting technology (ceramic metal halide, metal halide, and high-pressure sodium). LED lighting fixtures have a higher efficiency because more of the power input goes to light than heat as with HID. This efficacy metric can also be stated in terms of PPF (photosynthetic photon flux) to watts. For example, high pressure sodium is only about 1.7 vs. LED at approximately 2.5 (depending on manufacturer). This becomes an important metric when it comes to daily energy costs and HVAC requirement.

Also, there is no warm-up time required with an LED fixture and they are also free of mercury, making disposal much easier than other bulbs. In addition, LEDs provide superior functionality when used as a sole source of lighting, making them an attractive option for many growers.

It is also important to note that metal halides have to warm up for about 10-15 minutes or less before they can give out full light. They also need a cool-down period of about five to 10 minutes before restarting. For this reason, they are not recommended for locations where the lights will turn on and off frequently. This can occur in a greenhouse application on extremely cloudy days.

An independent test lab will take the chip manufacturer specifications and extrapolate an estimated life (in hours) based on it degrading 90% or less (L90) once it is put into a grow light application. The ceramic metal halide bulb, with an average lifespan of between 8,000 to 10,000 hours of 12-12 cycle, should be changed out every 6-8 months, whereas the LED will last 36,000 to 50,000 hours before it hits the L90 metric.

Lower Heat
The CMH lamps operate at a much cooler temperature than both MH and HPS bulbs thereby reducing the need for additional cooling equipment. However, CMH bulbs operate much hotter than LEDs.

On average, a CMH system will cost twice as much as a MH or HPS system. However, that cost is recoverable because the efficiency is greater which results in lower cooling costs. In addition, the lamp cost plus the labor costs due to lamp change-outs will also help recover the initial added investment. Although SpecGrade LED’s initial investment costs are higher than CMH, MH, and HPS systems, this cost is offset over the life of the system due to rated life, lower amounts of radiated heat, and modularity.

Unlike both metal halide and high-pressure sodium light sources, LED has no filament to burn out, again resulting in longer life. A filament is also much more vulnerable to even the minimal power surges—especially as it ages. The LED does not have a glass envelope that holds in toxic gases or mercury requiring special handling.

Water evaporation
Water evaporation, which is a function of heat and humidity, should absolutely be factored into your evaluation of which grow light system to purchase. Depending on where you live this can be a costly expense. And even if it isn’t today, it will be as planet resources become less abundant. On this note, as stewards of the land, it is our responsibility to use our natural resources very efficiently.

The ceramic metal halide, metal halide, and high-pressure sodium light sources all degrade relatively quickly thereby requiring a costly change-out when a lamp degrades. Any light source that degrades by more than 10% or to a life of less than 90% should be replaced. Therefore, you should evaluate the grow light based on an L90 metric (L70 commonly gets used in commercial applications).

Once again, because each species of plant has over 5 million years of DNA, the crop and the region of the seed must be factored into the equation in term of how much light intensity is required. In addition, there is the Law of Diminishing Returns. In other words, the additional light intensity will be disproportionate to the electricity costs and to the amount of radiant heat that will ultimately impact the HVAC system. So, certain plants’ yield will increase as the light intensity increases, but at a disproportionate cost.

For example, by increasing the intensity (wattage) to max-out flowering of a cannabis plant at 100%, you would need to go all the way to ~1200~1500 PPFD, thereby nearly doubling the light intensity for a small 15% gain from 800 PPFD. So, just because a manufacturer may market a grow light to have the highest levels of PPFD, it doesn’t necessarily mean it is the best.

To complicate things even further, an LED printed circuit board, when placed onto an aluminum substrate, can either throw heat onto the plant or away from it. The challenge for the cultivator is to determine which manufacturer of grow lights will provide the optimum light spectrum and light intensity to maximize profits.

PPFD Guidelines
Each stage of a plant’s development requires various levels of light or photon (PPFD).
Every strain of every plant is a little different, however, here are some general guidelines:

Veg is normally ~300 to ~600 PPFD for multilayered clients for standard size plants it tends to be two week veg.
Veg on larger plants can go up to ~600 PPFD if they are vegging for more than four weeks.

Cloning is very often ~75~150 PPFD but is very dependent on time spent and the layer size. Most lighting companies and cultivators use way too much light for cloning, and it’s likely to stress out the clones. ~400 PPFD for veg can also be stressful for plants if they aren’t really healthy.

It’s nice to be able to start clones at ~60~75 PPFD, then go up to 100~150 PPFD when they start to root. Then, start veg at ~250 PPFD and go up to ~400 PPFD after a few days. Even with flower, starting around ~300~500 PPFD is acceptable. Work up to ~800~900 PPFD over the course of a couple weeks. With the right design and dimmers, you can increase the intensity to prep the plants for the next transition. You can also push each stage of growth when the plants can take it, and back off if the plants have any negative reactions to anything.

Optimal PPFD levels of flowering plants are generally between ~900 and ~1000 PPFD.

Because inside every plant is millions of years of preprogrammed DNA, selecting a greenhouse’s artificial light source to supplement the sun can be a confusing decision. It will have long-reaching economic implications to the commercial grower in terms of crop yields, up-front investment, and ongoing expenses. Although LED technology is a relatively new technology, it has proven itself a viable light source for a wide range of crops. It positively impacts a variety of greenhouse factors, but the primary ones are efficiency and flexibility.

Indoor Applications

No matter what type of crop you are growing, what time of year it is, or how much natural sunlight is available, LED is likely to be a perfect cost-effective artificial light source.

LED grow lights can simulate long days or short days. Fine tuning the light recipe will supply spectra that can trigger early flowering or promoting delayed flowering without adding additional heat (and save on HVAC operating costs and water evaporation). It will give you more control over the greenhouse climate, in turn making year-round production possible. And finally, depending on where in the life-cycle a plant is and the manufacturer’s choice of electronic driver, the light intensity can be simply varied by using a low cost 0-10V dimmer.

Indoor Growing (Less is More)

LEDs, with their combination of low-profile design and maximum efficiency and performance, prove to be an excellent grow light to optimize every cubic inch of potential growing space while reducing water consumption and energy.

Vertical Farming

Vertical Farming applications, or producing plants in vertically stacked layers, requires a low-profile grow light that is designed for flexibility while delivering high levels of uniformity so that each plant gets the same amount of photons.

Single Level Growing

Basic single level growing from the floor will also require a grow light powerful enough to deliver high levels of PPFD and precision optics to minimize light spillage onto aisles and walls.

At a height of less than 6”, SpecGrade engineers have combined a low-profile design together with flexibility, maximum photon delivery, and uniformity in our Flora series. The more powerful Verta series will also provide the cultivator with exceedingly high levels of focused PPFD that will penetrate the plant’s canopy with minimal photon spillage into the aisles and onto the walls.

Wireless Control

Commercial LED technology in a greenhouse application can be integrated into a wireless mesh that will efficiently route data enabling the cultivator to control light intensity based on the age of the plant. Daylight harvesting sensors, an application commonly found in greenhouses, can be added to automatically reduce energy consumption by dimming in response to seasonable changing daylight availability as well as cloudy days.

When a cultivator evaluates the economics of LED to other technologies such as high-pressure sodium, metal halide, ceramic metal halide, and fluorescents in a greenhouse application, then using the proper LED system becomes even more compelling.

IP Rating stands for Ingress Protection Rating. To help ensure many years of seamless operation of grow lighting in an indoor farming environment, robust construction of the luminaire is required. An IP rating is available to assist you in the process of evaluating the correct grow light for a grow environment.

An IP rating is a two-digit international standard used to rate the level of protection against intrusion such as water, dirt, dust, and accidental contact with chemicals by using mechanical casings and electrical enclosures. It does not address UV protection standards (outdoor).

The first digit indicates the level of protection that the enclosure provides against access to hazardous parts (e.g., electrical conductors, moving parts) and the ingress of solid foreign objects.

The second digit indicates the level of protection of the equipment inside the enclosure against harmful ingress of water.

Because grow lighting equipment is commonly exposed to water, dust, dirt, humidity and high levels of ambient temperatures, on May 4, 2017 Underwriters Laboratory (UL) published UL8800, a set of safety requirements to be used when evaluating lighting equipment. This includes not only the luminaire but also non-permanent cords and plugs for indoor farming applications. Look for the UL safety mark before purchasing this type of equipment.

While the UL8800 certification will ensure safety, and the DLC certification will give you a performance confidence level, nothing will substitute for a traditional approach to construction. A grow facility is a harsh environment, and can impact the long term viability of your investment. The intense heat from the grow light, chemicals, water, higher temperatures, and being handled by people are all factors to be considered in decision making. Be aware that a few manufacturers are using plastic components, minimal heat sinking, and underrated drivers, and still qualify for the above-mentioned certifications. Robust construction is essential for your investment to stand the test of time.

The DLC (Design Lights Consortium) is an independent third-party certification body that most utilities will commonly look to before considering any rebates to owners of indoor farming facilities. Before putting a manufacturer on their Qualified Products List (QPL) list, they are required to meet a number of performance criteria.

To ensure electrical safety, make sure that the grow light has the mark of an independent third-party testing facility like UL (Underwriters Laboratory) and ETL. Request those test documents from any manufacturer you’re considering and then match them against the marketing materials and the mark for accuracy. Note that this is only one of many selection criteria.

Start by looking at the manufacturer’s warranties. Although robust warranties are a very good indicator of the company, as well as the products they are manufacturing, there are more questions to ask when researching a grow light manufacturer:

  1. How long have they been in business?
  2. What experience do they have in manufacturing LED fixtures?
  3. How does that experience relate to the indoor cultivation industry?
  4. Can they provide a resume of growers or testimonials that are either using or testing their products?
  5. What is social media saying about the company?
  6. Are they willing to provide you independent third-party test results?
  7. How quickly do they respond to your inquiries?

As LED fixtures produce light, they also produce heat. This is a critical issue on 3 different levels.

First, the higher the wattage, the greater the heat. And for every watt, 3.41 BTUs are required to cool. This is a major variable when it comes to specifying the electrical load in a facility and it obviously affects the ongoing electrical costs as well.

Second, the thermal management system in the fixture pulls the heat away from the LEDs and dissipates it, so that the heat-sensitive diodes do not fail prematurely.

Finally, the substrate (the aluminum board the LED is attached to) can also be engineered to direct heat away from the plants.

A passive technology called a heat sink is typically used to absorb unwanted heat, but there is a tremendous difference in the size and quality of heat sinks used in grow lighting. If the heat sink is poorly constructed, a motorized fan is often added to the fixture to assist in cooling it down.

Unfortunately, motorized fans are poorly suited to survive the conditions of a grow operation. The accessible vents and whirring blades are vulnerable to the bugs, dirt, water, debris, and chemicals commonly found in the space. Fixtures with motorized fans translate to more potential points of failure. If the motor or fan is damaged or unable to effectively cool the fixture, the LEDs are likely to overheat and fail, exposing an operation to down time that may compromise the crop. Avoid these potential pitfalls by selecting a grow fixture that uses a 100% passive thermal management system.

When a manufacturer or reseller provides you with their own internal performance test results, the results can be easily distorted by:

  1. The sample area they are testing
  2. An uncalibrated meter
  3. Old batteries

Test results from an independent third party are more reliable and should be made available to you.

If a manufacturer is unwilling to provide you with independent third-party test results to compare against their published ones, consider it a red flag.

Independent third-party performance test results are an excellent place to start, but they are good only when comparing like items. And, they won’t give you an accurate picture of what you can expect in your actual grow environment.

For example, an independent third party PPD test result does not factor in the cumulative effect of an area full of grow lights. More specifically, when you have a room full of grow lights the PAR from one light will inevitably spill over into the adjacent area, thereby increasing the averages. Actually, this spill-over effect is a more accurate measurement of what you can expect in your grow area(s). In addition, reflective surfaces will also factor into the equation. For example, a room painted with white surfaces will increase the light levels more than a room with concrete gray floors and unpainted block walls with a ceiling full of aluminum ductwork.

At the end of the day nothing takes the place of your own test grow as long as the variables are the same in each testing area. In other words, the plant’s strains, water, nutrients, and air circulation must all be the same. If you are unsure of which strain to test, then test your light and the spectrum with the strain you are likely to grow with before purchasing the light.

If you don’t have the luxury of time or the facility in which to perform a test grow, request supporting documentation from the grow light manufacturer. This can be in the form of a simple testimonial (with contact information) or a white paper.

Although all 3 PPFD calculations were made by an independent third-party testing facility using the same SpecGrade, 652-Watt Verta-8 top light, notice that the actual calculations vary significantly.

While Exhibit A and Exhibit B both measure a 4’x4’ area notice the average PPFD level drops by 58% when the light is raised over the canopy from 6” over the canopy to 36”.

Note also the maximum PPFD drops 283% from a high of 1169 in Exhibit A to 413 in Exhibit B. It reached that level only in one place because the light was within only 6” of the canopy.

However, when a whole room’s PPFD is calculated at 36” over the canopy the average using the same Verta-8 goes from 291 in Exhibit B up to 1058 in Exhibit C or 364%. This average is directly attributable to the multiple spillage effect of 200 grow lights on simultaneously in combination with the room’s surface reflectivity properties.

Finally, the important Avg/Min metric indicates the PAR uniformity ratio. A ratio of > 2.0 denotes excellent uniformity which will result in an even distribution of PAR which in turn will translate into uniform plant yields.