Copyright: Papillon Holland

People fear change. Even if the change is something that seems entirely logical to some people, to others, it could be completely inconceivable. For example, the earth used to be flat. Everyone knew that was the case. You would be ridiculous to suggest anything else. In fact, you would not only be ridiculous, but you would also be burnt at the stake for suggesting anything other than the official narrative dictates. The problem was of course that the earth wasn’t/isn’t actually flat. Science managed to overcome that little detail, although some people will still furiously argue that it is. Even now some people refuse to accept the change, holding on dear to their outdated ideals like some sort of metaphysical comfort blanket.

LEDs for commercial agriculture are in a somewhat similar position. Granted, it might not be quite as grand a concept as the shape of our planet, but the underlying sentiment is quite comparable. LEDs have come on leaps and bounds in recent years, and while the first generations may not have been wholly suitable for cultivating plants, they are now at the point where the possibilities are almost endless, even forcing a change into how we quantify light for agricultural practices. LEDs are now on the cusp of taking the plant lighting world by storm, almost only held back by the stoic nature of us mere mortals. So, let’s take a look at where they have come from, where they are and where they are going.

History of LED lights in general

Considering how recently LED technology seems to have come into the fray, it is surprising the technology was actually first stumbled across at the start of the 20th century. A British Engineer, named Henry Joseph Round, was tinkering around with radio detectors trying to improve how well they picked up a signal. As he tried passing a current through the material he was using he was surprised to note that some of the detectors were emitting light as he did so. He published his findings in ‘Electrical World’ in 1907, but nothing was done with the idea for another few decades.

A Russian was next to pick up the flag and run with it. Oleg Vladimirovich Losov spent a lot of time investigating the light emitted from the ‘Cats Whiskers’ style radio detectors, in particular when using zinc oxide and silicon Carbide based crystal rectifiers. He detailed findings, like the spectrum of light emitted, in a number of papers he published between 1924 and 1930. Losev was the first to recognise that the light that was coming out was not the result of thermal activities but from the properties of the semi-conductive material. A lot of his work was ‘lost’ during the siege of Leningrad between 1941 and 1944.

The next link in the chain came from Kurt Lehovic. He was a scientist from the then Nazi-occupied Czech Republic who was smuggled to the United States as part of ‘Operation Paperclip’ (where Nazi scientists and engineers were rounded up and sent to continue their work for America) in 1947. He filed a patent for a silicon carbide diode that emitted light in 1952, and from there went on to manipulate the colours of light produced by introducing different impurities in the Diode.

Copyright: Papillon Holland

LED’s in the commercial marketplace

Even with all this progression being made, it wasn’t until the late 1960’s that LED’s were used for any sort of commercial application. Not being particularly bright at this point though, LED’s were restricted to only being suitable as indicative blinkers on other technology. It wasn’t until 1987, that LED’s were developed to the point of being bright enough for actually illuminating an area. Car lights and traffic lights were the first to convert to LED’s and over the next decade or so, things really started to get going as the intensities and spectrums of light that LEDs could produce dramatically increased.

It was at this point that the plant geeks stepped in and decided to see how suitable this new LED technology was in growing plants. Barta et all, Bula et all and Morrow et al. were all publishing findings of LEDs and plant growth from 1989 onwards. Although of course the tests were limited to the quality of the LEDs at the time, it was clear there was a considerable amount of potential. From that time to the current day, LED technology has advanced at an exponential rate. Each generation far surpassing the last; similar to mobile phones, each generation being leaps and bounds ahead of the last.

It wasn’t until Japan in 1995 when a few scientists named S Nakamara, I Akasaki and H Imano developed extremely bright, blue LED’s that things really started to kick off for the horticultural market. With this development (earning them a NOBEL in 2014), LED’s became far more appropriate for use in agriculture and over the next decade or so, things only got better and better. Since 2010 LED’s were even trickling onto the commercial market, although at this early point the promise of what LED’s were capable of far surpassed what they could actually deliver in practice, particularly when up against the tried and tested technologies like High Pressure Sodium lamps, or even Metal Halides.

Today. LED is widely used in agriculture. Copyright: Papillon Holland

Over the past few years huge advancements have been achieved, now getting to a point where the possibilities of combinations of light spectrums and intensities are almost endless. Even regarding sheer efficiency, LED’s already outweigh their HPS rivals (2.7 umol/s compared to 2.1 umol/s) and the spectrum of light they produce can be completely customised. This scale of development has even given rise to a new metric standard of how to quantify light for plant growth, established by the American Society of Agricultural and Biological Engineers in 2017. The future of LED’s certainly is bright!

How They work

So, now we know where LED’s have come from and where they are at now, it is probably a good idea to understand how it is that LED’s actually work. When you look at them particularly against a typical lamp, they are a completely different kettle of fish. Gone are the days of having to produce heat to get light (by burning something), LED’s rely on something far more intriguing and complex. Here we will quickly go through the components inside an LED and see how it all works.

  1. Silicon Lense – Keeps everything contained and the Diode safe. The angle of the lenses somewhat contributing to the total spread of light the LED outputs.
  2. Wire bridge – A tiny little wire to bridge the gap between the anode and cathode, passing the current onto and through the semiconductive material.
  3. LED Chip
  4. Anode – Positive side: where the electricity comes in.
  5. Ceramic Substrate – Carrier of different components around the LED chip. Ceramics is used because it is gas-tight, guides warmth, and current isolated.
  6. Thermal solder pad – Provides an effective channel for heat transfer and optimizes thermal resistance from the LED chip junction to the thermal pad. The pad is electrically isolated from the anode or cathode of the LED.
  7. Cathode – Negative side: where the electricity goes out.

This is of course grossly over-simplifying the physical process within the Diode of how the light is actually released. However, other than a basic understanding of what constitutes an LED, the main thing to take from this is how far removed from a conventional lamp this technology is. It is not simply burning a material to get light. It is making use of the properties of a material on an atomic level, rather than just the going by the traditional method of simply heating something up.

A Heated Debate

A partly heated greenhouse area in winter. Image source: Adobe stock.

The production of heat is something that plays an important role in how LED’s are used in a practical situation, and to a degree, how well they can integrate into a marketplace that is well versed to  dealing with IR radiation. While they can give out an incredible amount of light, the difference in the physical performance of the lights means that you cannot simply swap an LED for an HPS light, keep everything else the same and expect to achieve the ideal result. You need to take these differences into account and apply them to how you control your environment as a result.

As no Infra-Red heat is generated, it does not ‘feel hot’ under the light. Therefore, they do not heat up a crop in the way the Sun does (or HID lighting does for that matter). This, of course, means that different methods of practice are required by the grower to achieve an ideal yield. As mentioned at the start of the article, people fear change! Although, it’s sometimes easy to see why. If a farmer has had successful results from the same methodology year after year, it is hard for him to conceive any different. Getting used to a different set of practices, even though you may achieve more, can be tiresome.

Where they are going

With the overall efficiency of LED lights now already at 2.7µmol/J and looking set to break the 3.0µmol/J boundary in the very near future, it is undeniable that growing with LED lights will soon become the norm. HPS and CMH simply cannot compete with this. It is not just the efficiency of light that LED’s now have on their side, but also the spectrum. Now at the point where a spectrum of light can be completely customised, allowing the grower to tailor their own specific recipe of light for the exact type of plant they are growing, the possibilities for LED’s are almost endless.

Copyright: Papillon Holland

It doesn’t stop there either. Further to having plant-specific light recipe’s, they can also be further tailored for each stage of the plant’s life cycle. The ideal ratios of light for the exact stage of life that a plant is in can be created (Although this of course only works on the understanding that we know what the ideal recipe of light for every plant and every stage of growth is). In turn, these light recipes only work on the understanding that we have actually quantified light in a way that incorporates every wavelength that affects plant growth, not just those responsible for photosynthesis.

Changing the Game

Which such technological boundaries being destroyed by LED lights, it has even got to the point where a new framework of metrics for quantifying light has been established. Morphological effects of different wavelengths outside the standard PAR range play a huge role in plant growth, and as such wavelengths outside the usual 4-700nm wavelengths are now incorporated. The American Society of Agricultural and Biological Engineers published: ANSI/ASABE S640 JUL 2017, Quantities and Units of Electromagnetic Radiation for Plants (Photosynthetic Organisms).

This standardisation essentially paves the way for future generations of lighting technologies and allows developers the potential of correctly investigating and quantifying the effects of wavelengths from 200-800nm, far beyond the sometimes limiting PAR regions of yesteryear. Without the huge leaps in technology that have been seen with LEDs, this framework would likely not have even been a consideration yet. If there has ever been a time to keep your eye on LED’s it most certainly is now!