I am not sponsored by any companies that make the products I recommend. However, as an Amazon associate, I earn from qualifying purchases made through provided links.

First off, let me say that there is not grow light on the market that will compete with the cost efficiency and the spectrum of sunlight. Of course, there is some argument as to whether indoor grown Cannabis is a higher quality than outdoor Cannabis, which in some cases, may be true. I believe in these cases, it is not the spectrum of the sunlight that is to blame, it is usually other environmental factors. If you are lucky enough to grow outdoors or have access to greenhouse growing in a good environment, I recommend you take full advantage of that. The purpose of this article is to educate you on indoor lighting and supplemental greenhouse lighting for Cannabis, it is not advocating that growing under synthetic light is the only proper way to do it.

There are a wide range of lighting options available to purchase including light emitting diode (LED) lights, high intensity discharge (HID) lights such as high pressure sodium (HPS), metal halide (MH), ceramic metal halide (CMH) lights, or fluorescent lights such as T5 lights. A beginning grower can be quite overwhelmed by the options, and many would just appreciate a recommendation of what kind of light to buy for their purposes. In this article, I will attempt to educate you on the pros and cons of each type of light and provide some recommendations of lights for different purposes and price points.

Just a disclaimer: I have only ever grown using MH/HPS lights. For me, the reason for this is simply the low up-front cost and an okay level of efficiency. If I had more money to spend, I would likely upgrade to a CMH bulb with supplemental red light and UV bulbs or a full spectrum high-quality LED with supplemental UV light.

Terms you need to know

Color Warmth– This term is only relevant for broad spectrum grow lights that have red, green, and blue light represented in the spectrum; ‘blurple’ (red and blue diodes) grow lights are not really represented in this measurement. While it is more useful to actually see the wavelength spectrum of your grow light, the color warmth measurement can give you an idea of what the spectrum is like. Color warmth is a description of how red or blue your eyes perceive the light emitted from your grow light. It is denoted by a number followed by the letter ‘K’, and is on a scale from 1,000K to 10,000K. The ‘K’ stands for Kelvin, but is not related to the unit of temperature.

2000K-3000K: Warm white, illumination appears yellowish-orangish (the spectrum has relatively more red light than other wavelengths; this is the range most broad spectrum grow lights fall in)

3100K-4500K: Cool white, illumination appears fairly neutral

4600K-6500K: Appears more similar to daylight and is more blueish than the previous two.

PPFD (Photosynthetic Photon Flux Density)

This is a spot measurement of how many photons are falling on a particular area withing a given time. It is measured in units of micromoles of photons per square meter per second. Though the units are in square meters, the measurement is usually taken with a small light meter, and so it is best to take multiple measurements at various locations around your grow area and average them together. An ideal lighting environment would have equal PPFD all over your grow area, but this is simply unattainable and different lights have different light hotspots and distributions. In general, Cannabis can tolerate a very high level of PPFD. Certain studies have shown that Cannabis photosythesis rates can be maximized at PPFD levels of 1500-2000 PPFD [8, 9] at normal CO2 levels. However, many also seem to agree that indoors at temperatures around 25C, PPFD over 1000 provides a negligible yield increase unless CO2 is also supplemented. It is hard to know for sure without repeating previous experiments.

Based on common ‘rule of thumb’ knowledge:

Most indoor growers should shoot for PPFD levels between 700-1000 across their grow space to maximize the photosynthetic rates of their flowering plants (though many have less). 700 PPFD is generally sufficient for a grow area with a good spectrum, but many growers like to have PPFD levels of 800+ across their grow area

Seedlings and clones grow well with PPFD levels of 100-200 PPFD

Established plants in the vegetative stage do well with PPFD levels of 300-600. However, I often provide my vegetative plants with the same amount of light as my flowering plants (around 800 PPFD), though I would recommend around 600 PPFD for cost efficiency purposes. I think vegetative plants can utilize a good amount of light and it helps them acclimate to flowering intensities.

PPFD is a measurement of PAR

PAR (Photosynthetically Active Radiation)

This is the amount of light available for photosynthesis, which lies between 400nm and 700nm, as described by the McCree curve shown below. This is essentially a measurement of energy harnessed by the plant in relation to the wavelength of the photon hitting the plant.

However, the long-held beliefs about PAR are being challenged, particularly by Professor Bugbee at Utah State University, proposing that far-red (700-780nm) light is more photosynthetically active than previously thought, and can have an effect on plant morphology (stetching, elongation, cell enlargement), and may also have a role in helping flowers initiate more quickly.

For quite a while, most LED grow lights were comprised of an array of only two different colored lights, red and blue. The was because the lights were designed to target the absorption spectrum of chlorophyll, shown below:

Retrieved from https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Chlorophyll_ab_spectra-en.svg/1200px-Chlorophyll_ab_spectra-en.svg.png

However, as can be seen by the McCree curve, all visible wavelengths are also photosynthetically active. Some pigments called carotenoids have been characterized as photosynthetically active for wavelengths up to 550nm. While known photosynthetically active pigments may not absorb green light very well, it appears that chlorophyll a and b can utilize green light in small amounts.

Green light is particularly effective at penetrating leaf tissues. Up to 80% of green light passes through a chloroplast, and it is able to penetrate far into the mesophyll cell layers [1]. In whole, a leaf is able to absorb up to 85% of incident green light as the light is refracted within a large area of leaf tissue. Up to 10% of green light is able to penetrate through leaves to the lower canopy as well [2].

At very high PPFD levels of broad-spectrum white light, geen light can actually stimulate photosynthesis more efficiently than red light. This is because at high light levels (which Cannabis is normally grown under), chloroplasts in the upper mesophyll cells can become ‘saturated’. As red light continues to be absorbed, excess energy can actually be dissipated as heat. However, green light is absorbed less efficiently than red light by a given chloroplast, and so it penetrates further and is able to be absorbed by chloroplasts in lower mesophyll cells that are not saturated, [1].

It has also been noted that light wavelength has a direct effect on plant morphology. For instance, it is common for growers to use metal halide lights during vegetative growth because it has a more blue spectrum than high pressure sodium lamps, and blue light tends to promote shorter, more bushy growth patterns. HPS lamps are generally used in flower because the more red spectrum is more photosynthetic efficient and may help in promoting flowering.

HPS lights are more efficient to run than MH lights, and some hypothesize that red light may help stimulate flowering. While it has not been shown in Cannabis, red light has been known to accelerate flowering in some other species [6]. Green light may act as a shade signal when in a high enough ratio to other wavelengths, resulting in plants that may stretch or induce flowering early [7]. In short, all wavelengths seem to have some effect on morphology of the plant, and sometimes different wavelengths can act antagonistically or synergistically, meaning that it is not fully understood how different types of lights are affecting the phenotype of the plant both morphologically and metabolically. The spectrum of the sun is amazingly even, and so the different wavelength ratios of different grow lights likely have phenotypic effects that are not fully understood. A representation of the spectrum of sunlight is shown below:

Image taken from https://www.ccs-grp.com/natural_lights/images/home/imgLed4.gif

PPE- Photosynthetic Photon Efficiency

This is a way to measure how efficient your grow light is at converting input energy to photosynthetically active radiation, measured in micromoles of PAR photons per Joule of energy. Some of the newest LEDs have an efficiency of over 2.0. A lot of the high quality LEDs from around 2014 were about 1.7 PPE, which at the time was comparable efficiency to double ended HPS lamps. A lot of LEDs of the time were actually less efficient than HPS lamps. I still have a couple blurple Mars 300 lights from around 2014 that are probably quite low on the efficiency scale.

How Do Different Grow Lights Work?

Fluorescent

Fluorescent lights are made of a glass tube under mild pressure. The tube is filled with an inert gas such as Argon and a small amount of liquid mercury. Electrodes at either end of the tube produce a voltage that sends electrons through the Argon gas from the cathode to the anode. This vaporizes the liquid mercury into the arc. Some of the electrons hit the mercury atoms, causing electrons in the mercury atoms to become excited to higher energy states. As the electrons drop back down to lower energy states, photons are emitted at UV wavelengths. Fluorescent tubes are coated in phosphor that shifts the wavelengths of the photons, resulting in a distribution of different wavelengths and a fairly broad light spectrum.

Fluorescent lights are the least useful lights on this list in my opinion. I would not use CFLs or T5s for anything other than rooting cuttings and/or small seedlings or maintenance of mother plants. They are not a bad choice for vegetative growth, but I believe metal halide and LED lights perform better and may be more efficient.

Most cheap LEDs that you would use to replace fluorescents for seedlings also tend to be composed of only red and blue diodes, which creates a very unnatural purple light. If you operate a dispensary keeping clones in a showroom for sale, the balanced spectrum from the fluorescents might be the better choice simply because it’s a bit more appealing to customers and the plants can be seen much better.

Because of the lower light output by fluorescents, they generally need to be kept pretty close to the top of your plants (around 6-10 inches).

LED

This paragraph will get a bit technical: LEDs (Light Emitting Diodes) are semiconductor light sources. This means that the conductivity of the material is in between that of a pure conductor and an insulator. Generally, there are three layers in an LED. The n-type semiconductor has an excess of electrons and the p-type semiconductor has an excess of ‘holes’, which are regions where electrons are absent in a crystalline lattice. These semiconductor types are made by adding different impurities to the materials. In between the two layers is an active layer that does not have an excess of electrons or holes. When a voltage is applied, excess electrons and holes from the n and p layers flow into the active layer, and when the electrons recombine with electron holes, they drop in energy states from the conduction band to the valence band. When this drop occurs, the difference in energy is released as a photon with a particular wavelength depending on the energy difference between the conduction and valence bands. The energy difference can be altered by changing the alloy composition. For instance, if the active layer is composed of indium gallium nitride, altering the ratio of indium nitride to gallium nitride can tune the bandgap of this material to different wavelengths of light. As you can likely guess, this means that each active layer can only emit a particular wavelength of light, which is why many grow lights will use a number of different colored diodes in order to provide light of different wavelengths to your plants. Broad spectrum LEDs can be made by coating blue LEDs with different colored phosphors, similar to fluorescent lights. This can shift the wavelength of blue photons, making emitted light come out in a broad spectrum of wavelengths. The typical phorphor coated LED spectrum looks something like this:

Image was sourced from https://www.researchgate.net/profile/Adoniya_Sebitosi/publication/3270698/figure/fig8/AS:668400070168582@1536370403195/Typical-emission-spectrum-for-a-phosphor-based-white-LED.pbm

Two major LED types are used in LED grow lights: SMD and COB.

SMD- Surface mounted diodes

large 5x5mm SMD LEDs are capable of housing up to 3 LEDs per module. These are diodes that do not require wires. Instead, they are soldered directly to a circuit board. Sizes vary greatly, from under 1mm squared to over 25mm squared. Most SMD circuit boards are 3W or 5W and are composed of 0.5W modules, although 10W SMD circuit boards do exist. Each diode in an SMD module has its own anode and cathode. Due to these properties, a variety of spectrums can be produced by SMD panels that can span the PAR spectrum.

COB- Circuit on Board

COB LEDs allow for multiple diodes (at least 9, but can be much higher) to be attached to a single substrate with a single circuit (one cathode and one anode). Diodes can be placed quite close to one another and produce a high light intensity for a small space. Most COB grow lights will have a mixture of warm white and cool white (3000K-4000K) diodes, resulting in a wide and benefiial spectrum for plants. Both COB and SMD LEDs are quite efficient, though a panel of 3W SMD LEDs is generally slightly more efficient than COB LEDs. COBs tend to have a much more focused light than SMDs, meaning that for the light spread to be useful over a large area, a lens usually has to be placed to increase the area that the light can reach.

HID Lights

HID stands for high intensity discharge. Like fluorescent lights, HID lights are arc lights. They work by forming an electric arc between two tungsten electrodes that are housed in an arc tube. The arc tube contains a noble gas that ignites when the circuit is active. The gas begins to heat up and eventually vaporizes metals within the arc tube. Light is produced when excited electrons drop in energy levels, releasing photons. The spectrum of the HID light is largely determined by the metal and impurities that are being vaporized in the arc tube. There are three main types of HID lights used in plant cultivation: HPS (High Pressure Sodium), MH (Metal Halide), and CMH (Ceramic Metal Halide).

HPS

As you can probably guess, HPS lamps contain sodium as the primary metal in the arc tube. Other impurities such as mercury are added to alter the spectrum of the lamp to have more blue wavelengths. HPS lights are dominated by orange, yellow, and red wavelengths, while still containing small amounts of blue and green wavelengths. The composition of the materials in HPS bulbs for horticulture has changed over time to try to make a more balanced spectrum. An HPS spectrum looks something like this (although each lamp is slightly different):

Image is from https://cdn.shopify.com/s/files/1/1788/3925/products/2k_1000w_HPS_2_1000x.jpeg?v=1489442504

Double ended HPS bulbs began to be popular for horticulture around 2014. Double ended HPS bulbs are slightly different because they don’t screw into a socket, they have electrodes at either end of the bulb similar to fluorescent tubes. DE HPS lamps, as mentioned previously, are more efficient than their single ended counterparts. For SE HPS bulbs, there are 4 common wattages, 250W, 400W, 600W, and 1000W. 600W bubs are the most efficient, while 1000W bulbs are second most efficient. 400W is less efficient still and 250 W bubls are the least efficient. As many long-time indoor growers know, HPS bulbs used to be the only way to grow indoors with high intensity light and they have been the gold standard of horticultural lighting for decades. Even today, HPS bulbs are some of the best flowering lights you can buy, though modern LEDs are quite competetive and arguably better. Because of the high amount of red light, HPS bulbs are generally only used for flowering. The red light of the HPS affects the structure of cannabis (during vegetative growth) causing it to become more lanky and weak in stem and branch growth.

MH (Metal Halide) MH bulbs also contain mercury, though in a higher concentration than HPS bulbs. However, MH bulbs have metal halides instead of elemental sodium as the light source. Metal halides are metals that are compounded with bromine or iodine. A MH spectrum might look something like this:

Image is from https://cdn.shopify.com/s/files/1/2815/4032/products/400w3_1947294c-d0f9-425e-a66a-b765e0b96f11_800x.jpg?v=1568192772

As you can see, there is very little red and far-red light in this spectrum as compared to the HPS bulb. This not only reduces the photosynthetic efficiency, it has an effect on plant structure, causing the plant to be more compact than it would under a red-light heavy spectrum. There is also very little far-red light.

CMH- Ceramic Metal Halide

CMH lights are the newest HID lights used in horticulture. They are more efficient than MH bulbs and also have more red in the spectrum. In fact, the CMH spectrum is fairly well balanced and could be compared to a mixture of MH and HPS bulbs. For this reason, they can be quite effective at both vegetative growth and flowering, growers don’t need to worry about switching out bulbs or even replacing bulbs as frequently. An example spectrum from a 3100K CMH bulb is shown below:

Image taken from https://lh3.googleusercontent.com/proxy/AaqZ6u-HRqoowBCkANpdee-AJpjKFpYCwh_14GehJinwIUPOWu1z6h8dIJpVgbvklA-CFsj_QfDmyVf2b2TzoYchibgP_O1FWMpChdsnXyn3FfPS

CMH bulbs also have a much longer lifespan than MH and HPS bulbs, and they produce far less heat than HPS bulbs. However, they are significantly more expensive than other HID options. Also, there is no 1000W CMH option; most of the CMH bulbs on the market are 315W or 630W double ended bulbs. Many believe that CMH bulbs may not be as effective as DE HPS bulbs in flower, but this is hotly debated. It is also important to look at the quality of the flower produced. CMH bulbs produce relatively more UV radiation and blue light, for example, which has been shown to be effective at stimulating the production of secondary metabolites such as cannabinoids and terpenes [10]. In the end, MH/HPS bulbs and CMH bulbs are both great choices, and each option has its positives and negatives. In fact, some growers will use both strategies in their grow area in order to take advantage of the broad spectrum of the CMH while also adding in supplemental blue-dominant and red-dominant light at different growing stages. One could also consider using HPS bulbs and supplementing with LED lights with a cooler color temperature to try to get a broader spectrum than HPS could provide by itself.

So, now that we have covered the basics of the different types of horticultural lights, how do you determine what to buy? Well, there is no right answer. If you spend any time on internet forums, you will soon realize that many different people feel quite strongly about their choice in light. My personal opinion is that it is best to mix different types of lights in order to reach the PPFD levels that you need at a spectrum that is acceptable. If you have a light or light mixture with a truly broad spectrum like a CMH bulb or broad spectrum LED, you don’t have to switch out lights for flowering. If you do not, it is best to stick to blue-heavy spectra for vegetating and red-heavy spectra for flowering.

How Expensive are Different Lights?

Cheapest (<$200/ sq. ft.)

If you are on a tight budget, I recommend a single-ended HID setup using a digital ballast that can support both MH and HPS bulbs (MH for veg, HPS for flower). This can cost less than $200 to light up 3 ft x 3 ft grow area, and you can even light up a 4 ft x 4 ft area using HID for less than $200, though I would not be comfortable doing the same with LEDs at this price point.

Mid-Range ($200-$400)

If you have a moderate budget ($200-$400)/ 10 square feet, and don’t want to have to worry about switching bulbs out, CMH lights are a very good option. DE HPS is a very good choice for flowering as well, and there are fixtures that can also run DE MH bulbs for veg. While CMH lamps can be quite good, some argue that they need some supplemental red light to help get the most out of flowering. CMH lights may be more efficient overall than a MH/HPS system since MH lamps tend to be less efficient than CMH and HPS lamps.

This price range also allows for some nice LED choices. For instance, the Mars Hydro TS3000W light is a good price for the light, but it uses some cheaper materials and designs for the fixture. It covers a 4 ft x 4 ft quite well and has a broad spectrum with some supplemental red light (SMD chips) and can be purchased for $480.000, giving an average cost of $27.5/1 square foot. There are also some cheaper COB and COB/SMD combo grow lights that can be purchased within this price range, though the COB LEDs used in these cheaper lights are usually either not a high quality full spectrum COB or they are not as powerful over a large area compared to SMD panels. A good 100W COB LED can be purchased at this price point, but it will not light up a 10 sq. food area well at all.

Big Budget ($400+ for 10 sq. feet)

This is the price range in which LED really shines. As I said, there are a lot of opinions out there about if LEDs really can outperform HID lights. However, a lot of people simply don’t have physics on their side. There is no magic to HID lights that make them the be-all-end-all of grow lights. If you have LED lighting with the exact same PPFD, the exact same distribution, and the exact same spectrum as an HID light, they will perform exactly the same. HID lights do not ‘penetrate’ better. Photons travel at the same speed regardless of what their source is, and in fact, the most important wavelengths for canopy penetration are green wavelengths. A well-designed full spectrum LED light will have more green light than HPS lights. Therefore, it is actually modern LEDs that have better penetration than HPS lights (although CMH lights tend to have good amounts of green light as well). Furthermore, no grow lights on the market can match the efficiency in PAR/Joule of the top tier LED grow lights.

For instance, for $1,000.00, you could purchase a Chilled logic 660 LED grow light, With an efficiency of around 2.4 PAR/Joule, an even distribution, and a broad spectrum with supplemental red wavelengths that looks like this:

Image taken from https://cdn.shopify.com/s/files/1/0504/4713/files/Spectrum_-_ChilLED_LOGIC_660_grande.jpg?v=1563915183

it is hard for HID lights to compete. The measured PPFD is similar to HID lights as well. The PPFD measurements over a 4×4 area are shown below:

Image taken from https://cdn.shopify.com/s/files/1/0504/4713/files/logic660-4×4-PARmap_grande.jpg?v=1563915187

I have not used this light, it is just one that I saw mentioned recently that I am using as an example of the kind of performance one can achieve with modern LED lights.

UV Lighting

Finally, it is important to consider whether or not you want to include UV light in your grow. For instance, UVB has been shown to increase cannabinoid levels in Cannabis [3], and many CBD and marijuana commercial growers are beginning to add UV light to their grows (specifically UV-B and UV-A).

UV-B (290nm-320nm) light appears to be sensed by the UVR8 photoreceptor and plays a stimulating role in producing secondary metabolites such as cannabinoids and terpenoids [3,4,5]. Essentially, UVR8 induces upregulation of genes involved in producing metabolites involved in defense against various environmental and biotic factors including sunlight. It is difficult to achieve the extremely high 30% THC levels found in some buds today without supplemental UV lighting. UV-A light has also been shown to increase cannabinoid levels [10], and does not cause DNA damage to cells. In fact, UV-A and far-blue light can activate DNA repair mechanisms through a process known as photreactivation that can mitigate some damage from UV-B [11]. UV-A is sensed through different proteins than UV-B including cryptochromes and phototropins and acts to repair DNA damage by upregulating the expression of photolyase proteins [12]. In the proper ratios, UV-A exposure can enhance plant response to UV-B light. Though UV-A exposure may help with secondary metabolite production, stimulation of the UVR8 pathway is very important to maximize the effects of UV light. In actual sunlight, UV-A is present in greater amounts than UV-B, and obtaining the proper ratio will be important for optimizing plant UV responses for the purpose of cannabinoid production. Most UV lights on the market do not have the same ratio as sunlight, but I believe it is important to at least make sure that the lights chosen have both UV-B and UV-A represented in the spectrum.

UV-B light is damaging to cells, and cannabinoids act as a suncreen, absorbing UV light in trichomes before the light reaches plant cells. This explains why UVR8 may participate in upregulating cannabinoid production. The best way to currently supplement plants with UV light economically is with UV T5 fluorescent bulbs, which can be purchased quite cheaply, and will provide both UV-A and UV-B light. Reptile UV lights and similar short-tube designs are not strong enough, and UV LED lights are too expensive simply for a supplemental light.

It is difficult to suggest how long to leave UV lamps on or when to start supplementing, as many people suggest pulsing the UV light for short periods of time, using them every other day, or only using during the last couple weeks of flower. However, many growers also advocate using them daily for multiple hours a day, even during vegetative growth (sometimes up to 12 hours per day). For instance, Lydon et al. 1987 found increased cannabinoid production after 40 days of exposure, and cannabinoid concentrations increased with dosage. In nature, UV radiation is present whenever visible radiation is, so it makes sense that the UV-B and UV-A radiation from a T5 won’t be too much for the plant to handle. I believe more optimization experiments are needed here, but I would say that my current recommendation would be to use daily, at least during the flowering cycle, for at least 4 hours per day, and up to 12 hours per day should be okay but the returns from longer time periods are likely diminishing. The one time I might cut back on UV exposure is during the last couple weeks of flower, after which cannabinoid production won’t increase by a large amount, but UV radiation might contribute to cannabinoid degradation. I would probably limit the expose to about 2 hours per day during the last couple weeks of flowering.

Product Recommendations (In no particular order): I will provide recommendations based on reviews and tests I have watched and read online, not based on testing all of these products personally. Recommendations are not ranked.

Fluorescent:

T5- With T5s, one can get a variety of fixtures and bulbs of different lengths, color temperatures, and number of bulbs.

Complete Kit (value): DuroLux T5 Grow Light (4ft 4lamps) DL844s Ho Fluorescent Bulbs- ($92 on Amazon)

Improved Spectrum LED T5s full kit: Active Grow with 8 x 24W T5 HO 4FT LED Tubes ($385) While this is better than standard T5s, it is overpriced compared to SMD or COB LEDs at similar watts in my opinion

Recommended fluorescent bulb for highest performance: Hortilux PowerVEG Full Spectrum with UV 54w – 4ft T5 HO Bulb ($28)

UV

For UV supplementation to any grow light system, I recommend using AgroMax Pure UV T5 bulbs.

2 ft.- $22

4 ft.- $28

Alternatively, the Hortilux PowerVEG proveds plenty of cool-white PAR as well as UV that would be a good supplement to HPS bulbs. ($28/bulb)

HID

In regards to HID fixtures, I think Vivosun and iPower are both good products that are a good value. I have had the iPower 600W ballast for around 6 years, and it is still running well.

HPS/MH– Keep in mind that different bulbs may have different color temperatures. For CMH, 3100K is a good color temperature in my opinion.

DE HPS/MH Fixtures (good values, good performance)

iPower ($259)

Vivosun ($226)

DE HPS Bulbs:

Best Value- Ushio brand ($74)

High Performance- Eye Hortilux ($94)

I would recommend the same brands for MH bulbs

Single-ended HPS/MH

Fixture

iPower 600W setup with wing reflector fixture ($120)- This is not air cooled, meaning that it will significantly heat your growing space, but will have greater efficiency since light does not pass through a layer of glass.

iPower 600W setup with air-cooled hood fixture ($150)

Bulbs

Performance: Eye Hortilux 600W HPS bulb- ($78)

Best Value: Ushio 600W HPS bulb Optired- ($55)This is the bulb I have. I like it quite a bit and lasts quite well

1000W HID Fixtures and Bulbs:

600W Fixtures and Bulbs:

CMH

HydroCrunch 630W DE CMH setup ($355)

Eye Hortilux 315W CMH setup ($463)- high quality and has a higher UV ratio in the spectrum than many CMH bulbs.

Vivosun 630W CMH fixture($230)- fits 2 315W bulbs

Eye Hortilux 315W CMH bulb ($92)

Ushio HiLux Grow 315W bulb ($82)

LED

High Performance

I mentioned the Chilled Logic 660 earlier, and I would recommend this light for a 4×4 space, but it will work in a 5×5 space, especially for a home grower. It uses SMD LEDs.

The Lumatek Zeus 600W is a fantastic SMD-based light with an extraordinarilly high efficiency of 2.3 umol/J. Like the Chilled logic, I recommend it for a 4×4 area with CO2 supplementation, but for a home grower it will perform great in a 5×5 area.

The California Lightworks 500W SolarXtreme is a fantastic broad spectrum COB-based fixture with a high-quality fixture. I recommend it over their red/blue SMD light, the SolarSystem 550

The Mammoth Lighting SMD 800W strip-lighting fixture can easily flower a 5×5 area with an efficiency of around 2.12 umol/J and costs around $1,000.

The HLG 550 V2 R-Spec quantum board can easily flower a 4×4 area and has a claimed efficacy of 2.6 umol PAR/J, though I am sure the actual PPFD/J is lower than the PAR/J figure. It will cost around $850

The Fluence SPYDR 2x and 2i lights are well known among commercial cultivators as being high quality and well designed for rack mounting. They have a claimed PAR efficiency of 2.7 umol/J, which again, likely doesn’t count the actual PAR landing on the plants.

Cheap but good

The Mars TS3000 is a great deal for home growers looking to light up a 4×4 area well and a 5×5 area decetly. It will run you about $440. The Efficiency is claimed to be around 2.2 umol/J, though the PPFD/J is likely lower than this.

The Spider Farmer SF 4000 will supposedly flower a 5×5 area quite well, has a claimed efficiency of 2.7 umol/J, and will run you about $570.

For a 2×2 area or supplemental lighting for HID lighting, a 100W CANAGROW CREE CXB3590 is a good choice and is lensed to give a wider range. It will run you around $150.

Of course, there are many other products that will work well. These are just products I have seen reviews on that are well-received.

Combinations

It is never a bad idea to mix and match lights in order to improve the light spectrum your plants are exposed to. Some combinations might look like this:

HPS bulbs for flower, supplemental cool temperature LED lights to increase blue and green light, and UV T5 bulbs

CMH bulbs for flower, supplemental red warm temperature LEDs to help with flowering, and UV T5 bulbs

Broad Spectrum LED lights with UV T5 bulbs

If you are doing combinations, you will want to slightly increase the spacing of your main light fixtures and to install supplemental lights in between your main fixtures. Make sure to space your lights so that your PPFD in any given area is not too high (wasting energy). Do not change spacing if only adding UV bulbs as these do not contribute to PAR.

Hopefully this has answered some questions!

Terashima, I., Fujita, T., Inoue, T., Chow, W. S., & Oguchi, R. (2009). Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green. Plant and Cell Physiology, 50(4), 684–697. https://doi.org/10.1093/pcp/pcp034 Growing Plants with Green Light – Greenhouse Product News. (n.d.). Retrieved February 22, 2020, from https://gpnmag.com/article/growing-plants-with-green-light/ Zavala, J., & Ravetta, D. (2002). The effect of solar UV-B radiation on terpenes and biomass production in Grindelia chiloensis (Asteraceae), a woody perennial of Patagonia, Argentina. Plant Ecology, 161, 185–191. https://doi.org/10.1023/A:1020314706567 Lydon, J., Teramura, A. H., & Coffman, C. B. (1987). UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH and CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES. Photochemistry and Photobiology, 46(2), 201–206. https://doi.org/10.1111/j.1751-1097.1987.tb04757.x Liu, H., Cao, X., Liu, X., Xin, R., Wang, J., Gao, J., Wu, B., Gao, L., Xu, C., Zhang, B., Grierson, D., & Chen, K. (2017). UV-B irradiation differentially regulates terpene synthases and terpene content of peach. Plant, Cell & Environment, 40(10), 2261–2275. https://doi.org/10.1111/pce.13029 What Effect Does Red Light have on Plants? | Ursa Lighting. (n.d.). Retrieved February 23, 2020, from http://ursalighting.com/effect-red-light-plants/ Zhang, T., Maruhnich, S. A., & Folta, K. M. (2011). Green Light Induces Shade Avoidance Symptoms. Plant Physiology, 157(3), 1528–1536. https://doi.org/10.1104/pp.111.180661 Chandra, S., Lata, H., Khan, I. A., & Elsohly, M. A. (2008). Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO. Physiol. Mol. Biol. Plants, 14, 4. Chandra, S., Lata, H., Mehmedic, Z., Khan, I. A., & ElSohly, M. A. (2015). Light dependence of photosynthesis and water vapor exchange characteristics in different high Δ9-THC yielding varieties of Cannabis sativa L. Journal of Applied Research on Medicinal and Aromatic Plants, 2(2), 39–47. https://doi.org/https://doi.org/10.1016/j.jarmap.2015.03.002 Magagnini, G., Grassi, G., & Kotiranta, S. (2018). The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L. Medical Cannabis and Cannabinoids, 1(1), 19–27. https://doi.org/10.1159/000489030 Britt, A. B. (1995). Repair of D N A Damage lnduced by Ultraviolet Radiation. In Plant Physiol (Vol. 108). http://www.plantphysiol.org Aphalo, P., Albert, A., Björn, L., Mcleod, A., Robson, T., & Rosenqvist, E. (2012). Beyond the Visible, A Handbook of Best Practice in Plant UV Photobiology.