Nowadays, using artificial light for cultivating plants is a common practice. If you were to take a wander through almost any commercial greenhouse, you would notice lighting fixtures installed in almost all of them. Like a lot of technologies, things have progressed at a very fast pace in a (relatively) short amount of time. For instance, if you were to ask your parents (or grandparents) about using artificial light for growing plants under, it’s quite likely they would screw their face up at you and think you were crazy for attempting anything other than growing outdoors, under the sun’s natural rays.
Now, the sun is a fantastic source of light: there is no denying that. Plants have evolved and developed alongside it for countless millennia. It would potentially be quite naïve to think we could improve on it. However, the problem we have on this humble spinning rock we call Earth is that things like seasonal shifts and weather patterns tend to obscure the sun’s brilliant rays. Daylight hours reducing with the changes in season, and huge cloud formations casting unwanted shadows can be the bane of farmers all over the world.
Did you know that from Earth’s perspective the sun is constantly moving in a figure-of-eight pattern?It’s called an analemma – a diagram that depicts the sun’s movement in the sky over a period of one year, when observed from a fixed position on the Earth. Photo Courtesy to: Giuseppe Donatiello
Where it all began
Queue supplemental artificial lighting. Despite this idea not reaching a mainstream audience until relatively recently, it may come as a bit of a surprise that using artificial lights to supplement plant growth began way back in the 1860’s.
In fact, the application of artificial lighting for plants almost went hand in hand with the development of lighting for people to be able to see at night. It just goes to show that fortunately for us modern-day farmers, there were plant geeks in every era!
Possibly the earliest source for investigating the effects of artificial lighting on plants goes back to the work of a couple of French guys: Mangon (1861) and Prilleux (1869).
Considering that Edison didn’t submit a patent for his first light bulb until 1879, it is clear to see that scientists were quick to imagine and realise the advantages that using supplemental lighting offered. Although, it was quite some time before the technology advanced to a point where it became practical for the average gardener to make use of it!
How it progressed
The advancement of artificial lighting technologies took three different paths as it developed through its infant years. Firstly, there was incandescent lighting, which was typified with Edison’s ‘invention’ of the incandescent filament lamp. Secondly, there was open arc lighting, which found its footing in the world by becoming the popular choice for industrial streetlighting. Thirdly there were enclosed gaseous discharge lamps, which were initially developed using mercury vapour in the late 1800’s. To begin with, open-arc technology was commonly the go-to technology for farmers. Siemens even ran a study with them in 1880 futuristically titled, ‘Electro-horticulture’.
It wasn’t until the 1900’s that the gaseous discharge lamps gained any headway in the evolution of artificial lighting, as it was around this time that green-fingered pioneers began to tinker with the traditionally mercury-based gases in the lamp. Sodium, Neon and Argon were some of the first gases to be included which showed great promise during trials at the Boyce Thompson Institute during the 1930’s. However, the true agricultural potential of this technology wasn’t realised until sodium (and Metal Halide) lamps were highly pressurised, in the 1950’s/60’s.
Sodium’s Under Pressure
High Pressure Sodium (HPS) Lighting currently holds the crown when it comes to indoor/supplemental lighting technologies. They are the most commonly used type of growing lamp in both commercial agriculture and the hobby market. Quite rightly so too, and for more than just a few reasons. They give the most efficient output in terms of raw power consumed versus actual light emitted. They have a great spectrum (colour) of light, offering a great blend of red/far-red. They also provide a good deal of infra-red, although this is now sometimes seen as somewhat detrimental to some growers, particularly those in smaller, more enclosed environments as it can be harder to deal with the associated heat.
If popular TV shows have taught us anything, it is that those who wear a crown will always be challenged by new blood as the evolutionary race continually perpetuates itself. The supplemental lighting world is no stranger to this principle! Metal Halide lamps have now been fortified with ceramic based filaments. Light Emitting Diodes (LED’s) are advancing at a breath-taking pace regarding both outputs and spectrums they can produce. It would seem that we are on the cusp of a technological arms race in the plant lighting world, and the throne is eagerly awaiting the victor.
What motivates technology advancements?
Of course, this boils down to a lot of factors, but the main two that consumers and farmers are really concerned about are the intensity of light a lamp emits, and the spectrum of light a lamp emits. These two factors drive everything that a plant does, and so whichever technology offers the greatest advantages in these two areas is likely to find itself atop the evolutionary heap. After these two factors things like production costs, resource costs, running costs and everything else come into play, but without a favourable intensity and spectrum, a lamp won’t see the light of day.
The light output of a lamp that is used specifically in photosynthesis. It is a measurement of photons of light within the Photosynthetically Active Range (PAR) of light, per watt of light being used every second (measured as µmol/w/s). Quite literally, a count of how many particles of usable light the lamp puts out for every watt of energy it consumes. The efficiency of a light bulb cannot be realistically represented by using Lumens, as this is a measure of how humans see light, not how plants use light, so be wary when you see this as a reference.
This is the overall colour of light that a lamp emits. Manufacturers will provide details about the wavelengths (colours) of light for every lamp they produce. The colour of a lamp, and particularly the ratio of one colour to another within the spectrum effects a plants morphology. For example, a higher ratio of far-red to red will induce a stretching in plants and a propensity to induce flowering. A ratio favouring blue will induce more compact growth between each plant node. Also, aspects outside of the PAR range (such as UV and NIR) can also have a direct influence plant growth
Understanding what motivates advancements in lighting technology all boils down to how well we understand how a plant grows in the first place.
What types of Lighting are there?
You can currently find a range of lighting technologies on the market, each with the own set of advantages and disadvantages. Unsurprisingly, there is no ‘one-size-fits-all’ solution, and each light will have more suitable applications than others. Here is a quick rundown of lighting technologies you will find available:
High efficiency top lightning LED fixture for fruits and vegetables. | Copyright: Papillon Holland b.v.
High Pressure Sodium
Currently the go-to lamp for crop production, providing one of the most efficient µmol/w/s with a spectrum that is in mostly the red bandwidth. Also, has a ratio of red to far-red that is highly suitable for flowering plants. Double-ended lamps are now the forefront of the technology with an output of up to roughly 2.1µmol/w/s (with an overall wall plug efficiency of roughly 1.9umol/w/s).
Metal Halide lamps tend to have a spectrum that lies much more towards the blue side of the PAR spectrum, that can induce a favourable morphology in vegetative growth. More energy is required to make a blue photon therefore they tend to have a lower overall efficiency than that of High Pressure Sodium’s when looked at in terms of just µmol/w/s.
Ceramic Metal Halide
Ceramic Metal Halide lamps have seen quite a surge in use since their development, thanks to having an exceptionally broad spectrum of light while still achieving a significantly high efficiency, roughly around 1.9µmol/w/s (with a wall plug efficiency of 1.67umol/w/s).
Having taken over the traditional lighting industry by storm, LED’s are now poised to take over the agricultural lighting market too. The technology has developed significantly over recent years, to the point where major commercial greenhouses have begun using them as a viable alternative to HID lighting. The best LED fixtures on the market at the minute, with their wall plug efficiency pushing a whopping 2.7µmol/w/s!
Greenhouse filled with efficient LED lightning. | Copyright: Papillon Holland b.v.
Tubes filled with gases, usually mercury, and pressurised to a low level. While not having an extremely high intensity, they do have significant practical advantages that make them suitable for a range of growing environments. Typically, their output and intensity make them ideal for small propagation areas, although with a wall plug efficiency of only 1.1µmol/w/s, LED’s may well take the lead here soon.
Why use supplemental lighting?
With all this advancement in lighting technology, it’s all too easy for useful information to go over the average layman’s head, bamboozling them into a position of ignorance. The investment needed in terms of both money and effort is quite a mental barrier for most hobby gardeners. Sure, it might look appealing, but without adequately understanding the advantages you can get from a product, why would you invest in something just because it looks nice and shiny? There are however a good few advantages you can gain by using supplemental lighting, that will give you quick and significant wins during every year of growing:
Early Starts: With even the most meagre of set-ups, you can begin germinating your seeds during the depths of winter, so when spring hits, you’re already leaps and bounds ahead of the season. A few small investments in low-intensity lights can set you months ahead of your competition!
Image source: Shutterstock
Extending Daylight hours: Plants use light in photosynthesis to make energy to grow with. When it gets dark, there is no light. During early springtime or late autumn, when the daytime hours shorten, you can gain significant extra growth by turning a supplemental light on for a few hours at the start and end of each day.
Mitigating shady days: Cloudy days for weeks on end are unfortunately quite commonplace, particularly here in the Western Europe! By turning installing an HPS or two in your greenhouse, you can keep your plants at peak production on even the dullest of days.
Full blown indoor growing: When you don’t want to leave anything up to chance, you can keep an entirely self-contained grow room away from the outside world altogether, pushing plants to the limit of production by controlling every environmental parameter down to a T.
Essentially using supplemental lighting is all about overcoming the limitations of natural lighting. Or looking at it another way, it’s about reducing the impact of seasonal and environmental factors on the light that makes your plant grow! Whatever level of grower you are, whether a budding hobbyist or commercial farmer, there is always a way in which you can enhance your growing from using indoor lighting.
What else to consider?
Every lighting technology will have a unique impact on the environment you put it in, other than just that of the quality of light. Most commonly, the heat created by the lamps will be the main thing to consider. For example, if you had a self-contained growing area with a 600w HPS light as the only light source, you can’t expect to swap it to the equivalent wattage LED light, change nothing else about your grow room or methods and achieve a comparable result. You’re likely to need to change many other aspects of your methodology, such as nutrient regime, plant training methods and environmental controls.
What’s best for you?
It all depends on your situation, in terms of the physical area you are growing in, what sort of crop you are cultivating but most significantly what you are looking to get out of your investment into supplemental lighting. Correctly understanding the differences between the technologies and how best you would apply each one to your situation is ultimately the key to getting the most out of your time and money.
As seems to be the case with pretty much any aspect of life, there is no one size fits all option, but it is currently a very good time in the evolutionary time line of agricultural lighting to make your choice!