Essentially, we know that controlling grow light spectrum can have a significant impact on areas of growth – like flowering, flavor, color, compactness etc. However, it’s important to recognize that signaling specific growth factors is part of a much larger, complex cycle. Results also vary depending on the environment (indoor or greenhouse), the relative temperature/humidity, crop species, light intensity (lumens per watt), and photoperiod etc.

Many growers take advantage of LED lights to help scale plant production due to their full light spectrum capabilities, low heat waste and maintenance, and extended lifespan. And given a plant’s physiology and morphology are strongly affected by specific spectrums, LED grow lights can efficiently promote growth in crops (2) at specific times in the growth cycle. With the ability to closely monitor quality, energy output can be easily evaluated for scaling crop production.

Cannabis growers – who pay attention to UVB/blue for its various structural and THC-potency benefits, which we’ll get into, are predominantly concerned with leaf size and flowering. Therefore, far-red and red light is relatively more important to boost their yields.

And finally, yield – this comes down to a combination of light spectrums and is often very unique to growers, including growers of several varieties of the same crop (like Cannabis). There’s no one single light spectrum that produces more of a crop – optimal lighting is very much a holistic, ever-changing process.

Pearcy, R. W., Muraoka, H., and Valladares, F. (2005). Crown architecture in sun and shade environments: assessing function and trade-offs with a three-dimensional simulation model. New Phytol. 166, 791–800. doi: 10.1111/j.1469-8137.2005.01328.x

Grow light spectrum refers to the electromagnetic wavelengths of light produced by a light source to promote plant growth. For photosynthesis, plants use light in the PAR (photosynthetic active radiation) region of wavelengths (400nm-700nm) measured in nanometers (nm).

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Marcelis, L. F. M., Buwalda, F., Dieleman, J. A., Dueck, T. A., Elings, A., de Gelder, A., et al. (2014). Innovations in crop production: a matter of physiology and technology. Acta Hortic. 1037, 39–45.

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Niinemets, U. (2007). Photosynthesis and resource distribution through plant canopies. Plant Cell Environ. 30, 1052–1071. doi: 10.1111/j.1365-3040.2007.01683.x

It’s worth noting photosynthesis is more complex than just chlorophyll absorption, but it’s important to recognize the fundamental principles.

Broad spectrum lighting – often referred to as full spectrum lighting, means the complete spectrum of light given by sunlight. This means wavelengths of broad spectrum lighting include the 380nm-740nm range (which we see as color) plus invisible wavelengths too, like infrared and ultraviolet.

Sarlikioti, V., de Visser, P. H. B., Buck-Sorlin, G. H., and Marcelis, L. F. M. (2011b). How plant architecture affects light absorption and photosynthesis in tomato: towards an ideotype for plant architecture using a functional-structural plant model. Ann. Bot. 108, 1065–1073. doi: 10.1093/aob/mcr221

Gu, L., Baldocchi, D. D., Verma, S. B., Black, T. A., Vesala, T., Falge, E. M., et al. (2002). Advantages of diffuse radiation for terrestrial ecosystem productivity. J. Geophys. Res. 107, 2–1. doi: 10.1029/2001JD001242

(6) Kalaitzoglou, P., van Ieperen, W., Harbinson, J., van der Meer, M., Martinakos, S., Weerheim, K., Nicole, C., & Marcelis, L. (2019). Effects of Continuous or End-of-Day Far-Red Light on Tomato Plant Growth, Morphology, Light Absorption, and Fruit Production. Frontiers in plant science, 10, 322. https://doi.org/10.3389/fpls.2019.00322.Available:

Mercado, L. M., Bellouin, N., Sitch, S., Boucher, O., Huntingford, C., Wild, M., et al. (2009). Impact of changes in diffuse radiation on the global land carbon sink. Nature 458, 1014–1017. doi: 10.1038/nature07949

Woolf, A. B., and Ferguson, I. B. (2000). Postharvest responses to high fruit temperatures in the field. Postharvest Biol. Technol. 21, 7–20. doi: 10.1016/S0925-5214(00)00161-7

(2) Darko, E., Heydarizadeh, P., Schoefs, B., & Sabzalian, M. R. (2014). Photosynthesis under artificial light: the shift in primary and secondary metabolism. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 369(1640), 20130243.Available:

Other indoor growers are also experimenting with the controlled use of far-red spectrum, like salad leaf farmers for example. Plants associate this spectrum with shading from direct sunlight, which would happen lower down the canopy, causing leaf & stem stretching as the plant reaches out for sunlight.

Stomatal responses to dynamic light vary dramatically among species, from virtually no response to rapid stomatal responses, thereby resulting in different consequences for instantaneous leaf photosynthesis (Knapp and Smith, 1990; Vico et al., 2011), which may subsequently modulate the effect of diffuse light on canopy LUE. Li (2015) have tested the responses of two anthurium cultivars which have distinct stomatal properties to diffuse light. In cultivars where stomata respond strongly to fluctuations of photosynthetic photon flux density (PPFD), transient rates of photosynthesis and subsequently LUE increased under diffuse light in which stomatal conductance becomes relatively constant and less limiting for photosynthesis. For cultivars with relatively insensitive stomata to the fluctuations of PPFD, the effect of the homogeneous temporal distribution of PPFD on LUE was non-existing. In this context, additional to benefits of diffuse light associated with improved spatial light distribution, the stimulating effect of diffuse light on crop LUE can also depend on the dynamic response of stomatal conductance to incident PPFD at leaf level.

It’s important to note light spectrums affect plant growth differently depending on things like environmental conditions, crop species, etc. Typically, chlorophyll, the molecule in plants responsible for converting light energy into chemical energy, absorbs most light in blue and red light spectrums for photosynthesis. Both red and blue light are found in the peaks of the PAR range.

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(c) Row crop systems are commonly used in horticultural and agronomic crops. This system facilitates crop management and allows higher light penetration inside the plant canopy. In this system, a fraction of light reaches the ground floor in the middle of the path (Stewart et al., 2003; Sarlikioti et al., 2011a), the reflection of light by the floor can be reused for photosynthesis. Furthermore, row orientation substantially affects canopy light interception (Borger et al., 2010; Sarlikioti et al., 2011a). These effects may differ between diffuse and direct light conditions.

*Correspondence: Tao Li and Qichang Yang, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agriculture Sciences, Zhongguancun South Street 12, Haidian, 100081 Beijing, China, ltao1985@163.com; yangqichang@caas.cn

(4) Naznin, M.T., Lefsrud, M., Gravel, V. and Azad, M.O.K. (2019). “Blue Light added with Red LEDs Enhance Growth Characteristics, Pigments Content, and Antioxidant Capacity in Lettuce, Spinach, Kale, Basil, and Sweet Pepper in a Controlled Environment.” Plants(Basel), 8(4). Available:

FIGURE 1. Light distribution in tomato canopy in the conventional clear glasshouse (direct light, A) and diffuse glasshouse (diffuse light, B) on a clear day. Light is more homogeneously distributed under diffuse light (B) compared with direct light (A) where many sunflecks in the middle and lower of the canopy. The photo was taken in Wageningen UR Greenhouse Horticulture, Bleiswijk.

This means when used strategically, bigger leaves and flowering can occur without unnecessary stress. So while there is no specific LED grow light spectrum for any particular plant, the ratio of red to blue light is very important to maximize growth and the rate of photosynthesis.

Crop photosynthesis to a large extent correlates with the light profile within the canopy (González-Real et al., 2007; Niinemets, 2007; Sarlikioti et al., 2011a). In the vertical profile of the canopy, light intensity decreases exponentially from top to the bottom of the canopy, as described by the Beer-Lambert–Bouguer law (Chandrasekhar, 1950; Monsi and Saeki, 2005) of which light extinction coefficient can be used to quantify the vertical light distribution in the canopy. Diffuse light exhibits a lower extinction coefficient than direct light (Urban et al., 2012; Li et al., 2014a) although the effect depends on solar position (Morris, 1989). This indicates diffuse light penetrates deeper into the crop canopy. Such phenomenon occurred due to the properties of diffuse light that scatters in many directions and thus causes less shadow, while direct light either concentrates in a beam or casts a shadow in the canopy, which results in the upper leaves being brightly illuminated and lower leaves in deep shade, or strong sunflecks at a given canopy depth. In the horizontal profile of the canopy, diffuse light also results in a more homogeneous light distribution due to less sunflecks occur (Acock et al., 1970; Li et al., 2014a), which plays the most important role for crop photosynthesis enhancement under diffuse light (Li et al., 2014a). A general impression of light distribution in the canopy under direct as well as diffuse light condition has been given in Figure 1. Apart from light distribution, diffuse light also resulted in a lower leaf temperature and less photoinhibition of top leaves (Urban et al., 2012; Li et al., 2014a), which are correlated with the lower light absorption of the top leaves as well as fewer local peaks in light intensity occur under diffuse light, these are also benefit for crop photosynthesis.

Knapp, A. K., and Smith, W. K. (1990). Contrasting stomatal responses to variable sunlight in two subalpine herbs. Am. J. Bot. 77, 226–231. doi: 10.2307/2444644

The peak of photosynthetic efficiency (light absorption) falls in the red light and blue light spectrums of the PAR range. Red radiation (around 700nm) is considered most efficient at driving photosynthesis – especially in the flowering stage for biomass growth (important to Cannabis growers). Blue light is essential for both the vegetative and flowering stages of plant growth, but mainly for establishing vegetative and structural growth.

A balanced pairing with blue light is necessary to counteract any overstretching, like disfigured stem elongation. It’s important to consider that while red is the most responsive light spectrum for plants, its efficacy really steps in when in combination with other PAR wavelengths.

Commercial grow lights can be wirelessly configured to put out specific wavelengths and intensities at certain intervals in a 24-hour cycle – grow light settings often work in conjunction with a grower’s HVAC systems too.With personal LED grow lights, lumens per watt will likely be lower – which makes them less energy efficient with smaller potential yields. Many are not broad spectrum and may only offer small spectrums of blue and red light. Additionally, while personal grow lights will still be inexpensive to run, other factors to be considered include noisier fans, inferior quality plastic casing, shorter LED lifespans and overheating issues.

So, what’s the ideal grow light spectrum for Cannabis? There’s no single spectrum since varying light exposure promotes certain plant morphology during different stages of growth. The chart below explains the concept of outer-edge PAR light spectrum use.

González-Real, M. M., Baille, A., and Gutiérrez Colomer, R. P. (2007). Leaf photosynthetic properties and radiation profiles in a rose canopy (Rosa hybrida L.) with bent shoots. Sci. Hortic. 114, 177–187. doi: 10.1016/j.scienta.2007.06.007

Research shows environmental stress, fungus, and pests can also be reduced using controlled amounts of UV. Research has emerged that suggests an increase in cannabinoids like THC (5) in Cannabis can be achieved using UV-B light (280nm – 315nm).

Red light is known to be the most effective light spectrum to encourage photosynthesis as it’s highly absorbed by chlorophyll pigments. In other words, it sits in the peaks in chlorophyll absorption. Red light wavelengths (particularly around 660nm) encourage stem, leaf, and general vegetative growth – but most commonly, tall, stretching of leaves and flowers.

Li, T., Heuvelink, E., Dueck, T. A., Janse, J., Gort, G., and Marcelis, L. F. M. (2014a). Enhancement of crop photosynthesis by diffuse light: quantifying the contributing factors. Ann. Bot. 114, 145–156. doi: 10.1093/aob/mcu071

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

RedLED wavelength

Falster, D. S., and Westoby, M. (2003). Leaf size and angle vary widely across species: what consequences for light interception? New Phytol. 158, 509–525. doi: 10.1046/j.1469-8137.2003.00765.x

Diffuse light improves spatial light distribution in the crop canopy, thereby stimulating crop photosynthesis; the more uniform horizontal light distribution within the canopy plays the most important role for this effect. Diffuse light also lessens the variation of the temporal light distribution at any specific point in the canopy. However, its effect on plant growth depends on the dynamic responses of stomatal conductance to the incident light. Apart from the homogeneous light distribution, diffusing the incident light makes it possible to allow more light in the greenhouse which strongly stimulates crop growth of shade-tolerant pot plants without compromising plant quality. Although the available knowledge have clearly stated the advantageous of diffuse light for crop production, incorporating the seasonal light condition and solar position, plant architecture, crop management practices as well as the post-harvest product quality for further research will strengthen our understanding of the effect of diffuse light on plant processes.

(a) The effects of diffuse light on crop photosynthesis could strongly differ between winter and summer light conditions. In winter, photosynthesis of the upper leaves is far from light saturation. With the same light intensity at leaf level, upper leaves have a higher rate of photosynthesis than lower leaves. Therefore, deeper penetration of light may have less effect on crop photosynthesis in winter (Sarlikioti et al., 2011b). Furthermore, light interception follows a seasonal pattern with on average, a lower fraction of light intercepted during summer than during winter because of changes in solar elevation (Sarlikioti et al., 2011a). The higher solar elevation in summer months results in an orientation of light rays more perpendicular to the plant canopy, resulting in a higher light penetration and lower interception. Therefore, seasonal variation of light intensity, directional light quality (diffuse or direct light) as well as solar position should be considered when exploring the effect of diffuse light on light distribution and crop photosynthesis.

Stewart, D. W., Costa, C., Dwyer, L. M., Smith, D. L., Hamilton, R. I., and Ma, B. L. (2003). Canopy structure, light interception, and photosynthesis in maize. Agron. J. 95, 1465–1474. doi: 10.2134/agronj2003.1465

The grow light spectrum for Cannabis varies when compared to other plants as growers are focused on maximizing yields, controlling levels of THC and other cannabinoid production, increasing flowering, and to maintain overall uniformity.

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Solar light is composed of a diffuse and a direct component. Diffuse light arises from the scattering of light by molecules or larger particles in the atmosphere and comes from many directions simultaneously; direct light arrives in a straight line from the sun without being scattered (Iqbal, 1983). Plants use diffuse light more efficiently than direct light (Gu et al., 2002; Farquhar and Roderick, 2003; Gu et al., 2003; Alton et al., 2007; Mercado et al., 2009; Li et al., 2014a), it arises due to diffuse light creates a more homogeneous light profile in the canopy than direct light. Photosynthetic rate of a single leaf shows a nonlinear response to the light flux density (Marshall and Biscoe, 1980). High light level usually leads to photosynthetic saturation and decrease in light use efficiency (LUE), which often occur under direct light condition. Therefore, the direct light usually wastes photons by concentrating the light resource to only a fraction of all leaves, leading to a less efficient photosynthetic use of light by plant canopies (Gu et al., 2002). Diffuse light, however, effectively avoids the light saturation constraint by more evenly distributing light among all leaves in plant canopies, and leads to a more efficient use of light (Gu et al., 2002).

UV light spectrum, which is not visible to the human eye, is outside the PAR range (100nm-400nm). Around 10% of the sun’s light is ultraviolet, and like humans, plants can be harmed from overexposure to UV light. Categorized into 3 types, UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm).

Long, S. P., and Humphries, S. (1994). Photoinhibition of photosynthesis in nature. Annu. Rev. Plant Biol. 45, 633–662. doi: 10.1146/annurev.pp.45.060194.003221

There are a few ways far-red can affect plant growth – one is to initiate a shade-avoidance response. At around 660nm (deep red) a plant senses bright sunlight exposure. From 730nm and beyond – i.e. a higher ratio of far-red to red light, a plant will detect light “shade” from another plant or leaves higher up the canopy, so stretching of stems and leaves occurs.

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Green wavelengths have been somewhat written off as less important for plant photosynthesis given it’s (in)ability to readily absorb chlorophyll compared to red or blue light spectrums. Nonetheless, green is still absorbed and used for photosynthesis; in fact, only 5-10% is actually reflected – the rest is absorbed or transmitted lower down! This is due to green light’s ability to penetrate a plant’s canopy

Asada, K. (1999). The water-water cycle in chloroplasts: scavenging of active oxygens and dissipation of excess photons. Annu. Rev. Plant Biol. 50, 601–639. doi: 10.1146/annurev.arplant.50.1.601

For photosynthesis to occur and chlorophyll to absorb the maximum amount of light for plant growth, plants use both blue and red light most efficiently. Other spectrums of light, like greens/yellows/oranges, are less useful for photosynthesis due to the amount of chlorophyll b, absorbed largely from blue light, and chlorophyll a, absorbed largely from red and blue light.

(1) Nelson, Jacob & Bugbee, Bruce. (2014). Economic Analysis of Greenhouse Lighting: Light Emitting Diodes vs. High Intensity Discharge Fixtures. PloS one. 9. e99010. 10.1371/journal.pone.0099010.Available:

Acock, B. J., Thornley, J. H. M., and Warren Wilson, J. (1970). “Spatial variation of light in the canopy” in Proceedings of the IBP/PP Technical Meeting, Trebon, Czechoslovakia. Wageningen: PUDOC, 91–102.

Hemming, S., Mohammadkhani, V., and Dueck, T. A. (2008). Diffuse greenhouse covering materials-material technology, measurements and evaluation of optical properties. Acta Hortic. 797, 469–475.

(d) Light distribution and absorption is highly dependent on crop architecture (Falster and Westoby, 2003; Zheng et al., 2008; Sarlikioti et al., 2011b). Short and compact canopies may generate substantial leaf overlap and self-shading, therefore decreases the net amount of leaf area exposed to light, and consequently affect canopy light interception (Falster and Westoby, 2003). Plants also vary widely in leaf angle, leaf orientation, internode length, and leaf length to width ratio, these traits have a direct effect on light absorption and photosynthesis (Falster and Westoby, 2003; Sarlikioti et al., 2011b). However, detailed research about plant architecture modulates the effect of diffuse light on light distribution and canopy photosynthesis are lacking. Furthermore, LAI is a predominant factor for canopy light interception, at low LAI mutual shading of leaves within the canopy is small, thus light may readily penetrate deeper into the canopy, which probably decrease the potential effect of diffuse light.

LED grow lights are energy-efficient lights used by indoor and greenhouse farmers and Cannabis growers too. Used as either a sole light source (indoor) or supplementary (greenhouses), LEDs help plants grow using full-spectrum lighting at a lower cost than traditional HPS lamps (1).

Li, T. (2015). Improving Radiation Use Efficiency in Greenhouse Production Systems. Ph.D. thesis, Wageningnen University, Wageningen.

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One advantage of LED grow lights is they can be set up to produce certain wavelengths for specified periods during the day or night. This makes it ideal for plants because growers can isolate specific spectrum colors depending on crops and growing conditions. Full spectrum lighting can also speed up or slow growth rate, enhance root development, improve nutrition and color etc.

This article aims to help you understand the light spectrums needed for plant growth and how full spectrum LED lighting is now widely used for crop production. We’ll address what broad-spectrum lighting is, how different grow light spectrums affect different stages of plant growth, and its effect on Cannabis production.

2024715 — 12 likes, 1 comments - studiobarrefit on July 15, 2024: " Barre Building Blocks: Light Weights By providing the extra resistance in ...

Borger, C. P. D., Hashem, A., and Pathan, S. (2010). Manipulating crop row orientation to suppress weeds and increase crop yield. Weed Sci. 58, 174–178. doi: 10.1614/WS-09-094.1

Even in northern countries, there are periods in summer with too high light levels for many shade-tolerant pot plants such as anthurium, bromeliads, and orchids. When excessive light energy is being absorbed by the light harvesting antennae at a rate which surpasses the capacity for photochemical and non-photochemical energy dissipation, this may lead to photoinhibition or photo-damage (Long and Humphries, 1994). In the long term, this could result in discoloring of leaves or even necrosis. Light damage occurs mostly as a result of prolonged exposure to excessive peaks in light intensity (Asada, 1999; Niyogi, 1999; Kasahara et al., 2002). Consequently, growers regularly apply shading in commercial production of many shade-tolerant pot plants in summer by closing a screen or having white wash on the greenhouse cover. However, shading often carries a penalty on potential crop growth as it is positively related to the amount of light that can be captured, which consequently reduces the LUE in the greenhouse production systems. When diffusing the incident light through cover materials, light in the greenhouse is more homogeneously distributed with less sunflecks, which decreases the extent of photoinhibition as well as local peaks in leaf temperature when global radiation is high (Li et al., 2014a). Therefore, the problem of discoloring of leaves or necrosis in shade-tolerant pot plants under relatively high light could be less when cultivated under diffuse light condition (Li et al., 2014b). Studies have suggested that increasing daily light integral under diffuse light not only accelerates plant growth but also improves plant ornamental quality with more compact plants (Li et al., 2014b; Marcelis et al., 2014). This may substantially contribute to the improvement of horticultural production.

Blue light spectrum is widely responsible for increasing plant quality – especially in leafy crops. It promotes the stomatal opening – which allows more CO2 to enter the leaves. Blue light drives peak chlorophyll pigment absorption which is needed for photosynthesis.

Sunlight produces a lot of greens, yellows, and oranges – they’re the most readily available spectrums of light. In fact, studies (3) tell us how green light, while not absorbed by chlorophyll as well as red and blue (hence why most plants appear green), it’s absolutely critical for photosynthesis.

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Monsi, M., and Saeki, T. (2005). On the factor light in plant communities and its importance for matter production. Ann. Bot. 95, 549–567. doi: 10.1093/aob/mci052

Wavelengthof blueLEDlight

Copyright © 2015 Li and Yang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

There’s a great deal of information and science to take on board as we understand the way plants interact with different light spectrums. Optimizing yield production and consistent quality of plants we’ve learned are attributed to light spectrums used together – much like natural sunlight.

Sarlikioti, V., de Visser, P. H. B., and Marcelis, L. F. M. (2011a). Exploring the spatial distribution of light interception and photosynthesis of canopies by means of a functional–structural plant model. Ann. Bot. 107, 875–883. doi: 10.1093/aob/mcr006

Urban, O., Klem, K., Ač, A., Havránková, K., Holišová, P., Navrátil, M., et al. (2012). Impact of clear and cloudy sky conditions on the vertical distribution of photosynthetic CO2 uptake within a spruce canopy. Funct. Ecol. 16, 46–55. doi: 10.1111/j.1365-2435.2011.01934.x

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Hemming, S., Mohammadkhani, V., and van Ruijven, J. (2014). Material technology of diffuse greenhouse covering materials – influence on light transmission, light scattering and ligh spectrum. Acta Hortic. 1037, 883–895.

Vico, G., Manzoni, S., Palmroth, S., and Katul, G. (2011). Effects of stomatal delays on the economics of leaf gas exchange under intermittent light regimes. New Phytol. 192, 640–652. doi: 10.1111/j.1469-8137.2011.03847.x

Alton, P. B., North, P. R., and Los, S. O. (2007). The impact of diffuse sunlight on canopy light use efficiency, gross photosynthetic product and net ecosystem exchange in three forest biomes. Glob. Chang Biol. 13, 776–787. doi: 10.1111/j.1365-2486.2007.01316.x

For growth, blue light is essential to help plants produce healthy stems, increased density, and established roots – all which occur in the early vegetative growth stages. Growth then continues with increased red light absorption, resulting in longer stems, increased leaf and fruit/flowering etc. It’s here that red light plays the dominating role in plant maturity and, therefore, size.

Zheng, B., Shi, L., Ma, Y., Deng, Q., Li, B., and Guo, Y. (2008). Comparison of architecture among different cultivars of hybrid rice using a spatial light model based on 3-D digitising. Funct. Plant Biol. 35, 900–910. doi: 10.1071/FP08060

Plants use diffuse light more efficiently than direct light, which is well established due to diffuse light penetrates deeper into the canopy and photosynthetic rate of a single leaf shows a non-linear response to the light flux density. Diffuse light also results in a more even horizontal and temporal light distribution in the canopy, which plays substantial role for crop photosynthesis enhancement as well as production improvement. Here we show some of the recent findings about the effect of diffuse light on light distribution over the canopy and its direct and indirect effects on crop photosynthesis and plant growth, and suggest some perspectives for further research which could strengthen the scientific understanding of diffuse light modulate plant processes and its application in horticultural production.

(5) Magagnini G, Grassi G, Kotiranta S. (2018), The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L, Med Cannabis Cannabinoids, 1:19-27. Available:

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Pearcy, R. W., Krall, J. P., and Sassenrath-Cole, G. F. (2004). “Photosynthesis in fluctuating light environments,” in Photosynthesis and the Environment, eds R. Neil and Baker (Amsterdam: Springer), 321–346.

Obviously, diffuse light has great advantageous for plant growth. However, detailed studies about the following aspects that closely related with diffuse light are lacking. Further exploring these aspects will strengthen the scientific understanding of diffuse light modulate plant processes as well as its application for crop production.

Lawson, T., and Blatt, M. R. (2014). Stomatal size, speed, and responsiveness impact on photosynthesis and water use efficiency. Plant Physiol. 144, 1556–1570. doi: 10.1104/pp.114.237107

In greenhouses, due to the presence of sunlight, supplementing green light spectrum using LED grow lights would be less important compared to crops are grown solely indoors – like Cannabis or vertical crop farming.

This work was supported by the National High-tech R&D Program of China (863 Program) under contract number 2013AA102407.

Nanometers are a universal unit of measurement but also used to measure spectrum of light – humans can only detect visible light spectrum wavelengths (380-740nm). Plants, on the other hand, detect wavelengths including our visible light and beyond, to include UV and Far Red spectrums.

GreenLED wavelengthrange

Farquhar, G. D., and Roderick, M. L. (2003). Pinatubo, diffuse light, and the carbon cycle. Science 299, 1997–1998. doi: 10.1126/science.1080681

For example, an increase in far-red (750nm-780nm) can help stimulate Cannabis stem growth and flowering – something growers want, whereas necessary blue light in minimal amounts, can prevent uneven elongation of stems and leaf shrinkage.

Niyogi, K. K. (1999). Photoprotection revisited: genetic and molecular approaches. Annu. Rev. Plant Biol. 50, 333–359. doi: 10.1146/annurev.arplant.50.1.333

The ideal grow light spectrum for plants depends on several factors. These include how specific plants use PAR-spectrum light for photosynthesis but also the wavelengths outside of the 400-700nm range. This light can help accelerate flowering, increase nutrition, speed up rate of growth, etc. If the light source is sole (indoors) or supplementary (greenhouses) also affects which grow light spectrums should be used.

Kasahara, M., Kagawa, T., Oikawa, K., Suetsugu, N., Miyao, M., and Wada, M. (2002). Chloroplast avoidance movement reduces photodamage in plants. Nature 420, 829–832. doi: 10.1038/nature01213

To investigate the effect of diffuse light on plant processes, many studies have been carried out by comparing plant responses on cloudy and clear days (Zhang et al., 2011; Urban et al., 2012); or by comparing the aftermath of volcanic and anthropogenic emissions (Gu et al., 2003; Mercado et al., 2009). Such type research implies not only a difference in the fraction of diffuse light, but also large differences in light intensity, and the subsequent changes in microclimatic parameters such as air and soil temperature, and vapour pressure deficit (VPD). These changes directly or indirectly influence plant processes. Recently diffuse glass has become available that increases the diffuseness of light without affecting light transmission in the greenhouse (Hemming et al., 2007, 2008, 2014). Studies have reported that such cover materials have a remarkable effect on plant growth and production (Hemming et al., 2007; Li et al., 2014a,b). Thus, the occurrence of diffuse glass not only provide a promising measure for improving horticultural production, but also offers an opportunity to explicitly explore the pure effects of diffuse light on light distribution over the canopy and its direct and indirect effects on crop photosynthesis and plant growth. In this review, we will discuss the effect of diffuse light on plant processes and its application in horticultural production, and subsequently point out the perspectives for further research.

Light spectrums outside of blue and red wavelengths are used least by plants to grow as reds and blues are where most photosynthetic activity occurs – a big reason why full-spectrum grow lights are incredibly efficient because a grower can get very specific.

WhiteLED wavelength

The above chart shows the PAR range – the spectrum of light plants use for photosynthesis. Grow light spectrum charts like this include both the PAR range and other spectrums as it’s been discovered that wavelengths outside of the PAR range are also helpful for plant growth.

While the benefits of ultraviolet light use in horticulture are still being researched, UV light is often associated with darker, purple coloring – in fact, small amounts can have beneficial effects on color, nutritional value, taste, and aroma.

LEDlightwavelength chart

Pearcy, R. W. (1990). Sunflecks and photosynthesis in plant canopies. Annu. Rev. Plant Biol. 41, 421–453. doi: 10.1146/annurev.pp.41.060190.002225

Aside from visible colors, Cannabis responds especially well to wavelengths just outside of the PAR range. Therefore, an added benefit of using full spectrum LEDs is the ability to use specific doses of ultra-violet wavelengths (100-400nm), and far-red wavelengths (700-850nm) outside of the PAR range.

The difference with personal vs commercial grow lights for Cannabis can be determined by a number of factors. Firstly, the available light spectrums in commercial LED grow lights will include the full PAR range and beyond – which is particularly advantageous for Cannabis growers.

Paradiso, R., and Marcelis, L. E. M. (2012). The effect of irradiating adaxial or abaxial side on photosynthesis of rose leaves. Acta Hortic. 956, 157–163.

Far-red can be very useful to promote flowering, and in certain plants, increase fruit yield (6). In short-day plants like Cannabis, which rely on longer periods of darkness, 730nm can be used at the end of a light cycle to promote flowering. Many growers are experimenting with interrupting the dark cycle with bursts of red light to boost growth and flowering.

(3) Hayley L. Smith, Lorna McAusland, Erik H. Murchie . (2017). Don’t ignore the green light: exploring diverse roles in plant processes, Journal of Experimental Botany, Volume 68, Issue 9, 1 April 2017, Pages 2099–2110,Available:

At BIOS we’re constantly developing our knowledge and research of how light spectrums on specific crops and strains work best – and at which time during a plant’s light cycle. Our LED grow lighting systems are designed and developed using detailed scientific research to give growers the control of using the ideal light spectrum for optimizing the yield, quality, and variability of their plants.

Generally, photosynthetic efficiency occurs at the red and blue peaks which means plants absorb these spectrums most when growing. You might think the ideal grow light spectrum is equal to sunlight – after all, it’s had millions of years of experience – however, it’s more detailed than this.

Physiological and morphological properties of plant organs can be affected by their prevailing growth microclimate (Sultan, 2000; Niinemets, 2007). A homogeneous light distribution within the crop canopy under diffuse light gives rise to the question whether plant physiological and morphological acclimation occurs. Diffuse light penetrates deeper into the canopy; thus, the lower positioned leaves receive on average a higher light intensity which leads to a higher total nitrogen and chlorophyll content in the canopy, and consequently results in a higher leaf photosynthetic capacity in the lower of the canopy (Li et al., 2014a). Acclimation to diffuse light also includes acclimation of leaf morphology, which affects light interception and, consequently, photosynthesis (Pearcy et al., 2005). Li et al. (2014a) reported that tomato plants grown under diffuse light showed a lower specific leaf area (SLA) which indicates a thicker leaves, as well as a higher leaf area index (LAI) which mainly caused by a greater leaf width. A higher LAI is highly relevant for crop photosynthesis, as long as the fraction of light interception is also increased. For the mature crop under greenhouse condition, which often has a closed canopy, thus, the increased LAI under diffuse light has limited effect on canopy light interception and photosynthesis for mature crop (Li et al., 2014a).

Way, D. A., and Pearcy, R. W. (2012). Sunflecks in trees and forests: from photosynthetic physiology to global change biology. Tree Physiol. 32, 1066–1081. doi: 10.1093/treephys/tps064

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

YellowLED wavelength

In nature, temporal light distribution in the canopy is characterized by alternating periods of relatively high light followed by periods of background low light at a given point (sunflecks). Under these circumstances, a large fraction of CO2 assimilation may occur under transient light conditions. Stomata regulate carbon uptake of a leaf. In response to fluctuating light, stomata exhibit a dynamic response that is slower than the response of photosynthesis and fluctuating light itself, which may limit the CO2 assimilation under fluctuating light conditions (Pearcy et al., 2004; Lawson and Blatt, 2014). In greenhouses, the shadow and sunflecks generated by overstory leaves, leaf movement, greenhouse construction parts as well as equipment may exacerbate the variation of temporal light distribution. This may substantially limit crop photosynthesis compared to constant light intensities (Pearcy, 1990; Way and Pearcy, 2012). This variation in light intensity can be minimized when the incident light is made diffuse, which would consequently lead to less limitation on leaf photosynthesis, thus improving the canopy LUE (Li et al., 2014b).

(e) Fruit and vegetable quality is closely correlated with the pre-harvest growth condition. In open field and conventional clear greenhouses, fruit and vegetables often experience diurnal fluctuations or long-term exposure to direct sunlight, with associated high tissue temperatures. This may result in harvest disorders (i.e., sunburn), and heterogeneity of internal quality properties such as sugar content, tissue firmness, mineral content (Woolf and Ferguson, 2000). Fruit with different temperature histories will also respond differently to postharvest low temperatures (i.e., chilling injury) (Ferguson et al., 1999). The quality problems induced by sunlight exposure could be reduced if plants were grown under diffuse light where less fluctuations in temperature and light intensity occurs, detailed research in this aspect has not been reported so far.

Marshall, B., and Biscoe, P. V. (1980). A model for C3 leaves describing the dependence of net photosynthesis on irradiance. J. Exp. Bot. 31, 29–39. doi: 10.1093/jxb/31.1.29

Hemming, S., Dueck, T. A., Janse, J., and van Noort, F. (2007). The effect of diffuse light on crops. Acta Hortic. 801, 1293–1300.

Citation: Li T and Yang Q (2015) Advantages of diffuse light for horticultural production and perspectives for further research. Front. Plant Sci. 6:704. doi: 10.3389/fpls.2015.00704

Ferguson, I., Volz, R., and Woolf, A. (1999). Preharvest factors affecting physiological disorders of fruit. Postharvest Biol. Technol. 15, 255–262. doi: 10.1016/S0925-5214(98)00089-1

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In some crops, blue light can benefit nutritional levels and coloring, and a higher red to far-red ratio can help with leaf size and flowering. It’s why today’s full-spectrum LEDs are so advanced – because by selecting the right quantities of red and blue light (4), chlorophyll pigments absorb more light they need.

Certain light spectrums trigger growth characteristics in plants. In general, blue light spectrums encourage vegetative and structural growth and red light promotes flowering, fruit, leaf growth, and stem elongation. Each crop type is sensitive to different spectrums and quantities of light at different times throughout a daylight cycle – this directly affects the rate of photosynthesis.

The use of LED grow lights in crop farming has recently seen substantial growth. However, choosing the right light spectrum for plants and knowing how they affect photosynthesis, can be challenging and oftentimes confusing.

Sultan, S. E. (2000). Phenotypic plasticity for plant development, function and life history. Trends Plant Sci. 5, 537–542. doi: 10.1016/S1360-1385(00)01797-0

Li, T., Heuvelink, E., van Noort, F., Kromdijk, J., and Marcelis, L. F. M. (2014b). Responses of two Anthurium cultivars to high daily integrals of diffuse light. Sci. Hortic. 179, 306–313. doi: 10.1016/j.scienta.2014.09.039

Gu, L., Baldocchi, D. D., Wofsy, S. C., Munger, J. W., Michalsky, J. J., Urbanski, S. P., et al. (2003). Response of a deciduous forest to the Mount Pinatubo eruption: enhanced photosynthesis. Science 299, 2035–2038. doi: 10.1126/science.1078366

It’s essential for seedlings and young plants during vegetative stages as they establish a healthy root and stem structure – and especially important when stem stretching must be reduced.

Morris, J. T. (1989). Modelling light distribution within the canopy of the marsh grass Spartina alterniflora as a function of canopy biomass and solar angle. Agric. For. Meteorol. 46, 349–361. doi: 10.1016/0168-1923(89)90036-1

Zhang, M., Yu, G. R., Zhuang, J., Gentry, R., Fu, Y. L., Sun, X. M., et al. (2011). Effects of cloudiness change on net ecosystem exchange, light use efficiency, and water use efficiency in typical ecosystems of China. Agric. For. Meteorol. 151, 803–816. doi: 10.1016/j.agrformet.2011.01.011

(b) Measuring leaf photosynthesis is the basis for estimating canopy photosynthesis. Conventionally, only the adaxial side of the leaf is illuminated by the light source when measuring single leaf photosynthesis, this might result in minor error in estimating the canopy photosynthesis under diffuse light. This is because diffuseness of light may affect the fraction of light on the abaxial leaf surface, while the abaxial surface have a different photosynthesis light response curve than adaxial surface (Paradiso and Marcelis, 2012). Therefore, measurements of light absorption and photosynthesis light response curves on both the adaxial and abaxial side of leaves in the canopy in combination with functional–structural plant modeling might help to estimate these effects.