Food production isn’t often the first sector that comes to mind when we think of technology. To remedy that, third year PhD student at the University of Reading, Emily Johnstone, explains how tuneable LED lighting is advancing research into fruit crop growth.

The current focuses of the Soft Fruit Technology Group at the University of Reading are out of season strawberry production to decrease UK reliance on imports during winter, speed growing, multi-tiered production systems, and optimising the spectral composition of LED lights during fruit production of strawberries. Emily Johnstone’s research sits within the latter, focusing on using LED lighting to propagate high-flowering strawberry plants which could produce up to 50% more fruit compared to plants propagated under standard conditions.

The move to LEDs

In the UK, Junebearer strawberry plants (or those which fruit in June) are widely grown both commercially and domestically. Many of us know that the number of flowers produced indicates how much fruit a plant can be expected to bear in the summer; that number is determined during ‘flower initiation’, which occurs during propagation the previous autumn.

Previous research at the University of Reading showed that propagating plants in heated glasshouses with supplementary high-pressure sodium (HPS) lighting at the beginning of autumn resulted in better flowering potential, and consequentially a higher berry yield (Twitchen, 2018) — however, a large proportion of the berries were below marketable size required for commercial companies, which has since increased even further.

Since this research was conducted, the industry has moved away from HPS lighting and adopted light-emitting diodes (LEDs) as standard. Although LEDs were first produced in the 1960s, their widespread application in agricultural growing systems has only recently been popularised because initial set-up costs have decreased and energy prices have increased, making older systems inefficient. My research aims to adapt the previous HPS growing model for use with LEDs, continuing to produce high-flowering strawberry plants, increasing berry production, and specifically increasing the proportion of marketable berry yield.

Optimising light

The spectrum of light is divided into colours based on wavelength, and each part of the spectrum triggers specific growth characteristics. Red and blue light both encourage photosynthesis; red promotes stem elongation (producing taller plants), flowering and fruit, while blue promotes vegetative, or leaf and root, growth while discouraging stem elongation.

HPS lights emit predominantly red light, which is ideal for supplementing natural light in a greenhouse during fruit production. However, LEDs produce the widest range of ‘photosynthetically active radiation’ (PAR) and can emit a higher proportion of blue:red light, which is more desirable during propagation where vegetive growth is encouraged or when space is limited, for example in some multi-tiered growing systems, where shorter plants are desirable.

LEDs have an additional benefit of producing much less heat than HPS lights, allowing testing of high intensity lighting without significantly impacting the temperature of the environment. The more recent development of remotely tuneable LEDs also means that the spectral composition of the light emitted can be carefully tailored; this hugely increases our ability to research the impact of light quality on crop growth and yield, and additionally enables the creation of a continuous growing environment where light can be altered to plants’ needs throughout their development.

Remotely tuneable LEDs have further benefits; firstly, that the lighting can be monitored and changed without the need for physical human intervention reduces the need to manually swap out lights or relocate plants. This has many applications for both research into and growing facilities for a wide range of plants where limited human intervention is either practical or required for the growing conditions, or where the facility is small and unable to store additional lighting or plant material.


The adoption of remotely tuneable LEDs has increased our ability to create finely tuned growth environments while simultaneously reducing the necessary resources for crop growth and research, supporting the sustainability and economic viability of space saving crop growth solutions such as vertical farms as well as enabling increased and higher quality research output.

Burning questions

Georgia Smith MBCS also had the opportunity to chat with Emily about her research, finding out more about the role of technology and AI, the potential application for vertical farming, and the carbon footprint of modern vs old school farming techniques.

Advances in multi-tiered growing systems like vertical farms have exciting potential for sustainable farming. Do LEDs benefit such systems?

Vertical farms benefit from LEDs for several reasons. Firstly, reduced heat output tiers can be put closer together without the plants getting too hot; although there’s a small negative that the heat from any light source will always heat the root system of the tier above, LEDs minimise this. Additionally, tuneable spectrums allow for the mimicking of natural light on lower tiers where it is unable to reach.

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To what extent are humans involved in controlling the environment?

Lighting, temperature, humidity and irrigation can all be automated to regulate themselves based on predefined settings, so human involvement for environmental control can be limited to purely defining the environment through those settings and checking the equipment is working. However, the more control you want over the system the more costly it will be, as many companies have annual licensing fees to use their software to control the environment.

What role does technology play in measuring your results?

Measuring the light quality given by the LEDs is done using a spectral PAR meters, but measuring the effect on the plant is still quite labour intensive; for example, leaves need to be manually counted, fruit is harvested manually, and photosynthesis needs to be measured using an IRGA. There is a lot of current research into using pictures of the crop to predict when the fruit will need harvesting and how much you can expect to get, which is very valuable information — but many factors impact these results, from the climate to pests and disease. The results are progressively harder to predict the further in advance you are.

Do LEDs use less energy/have a lower carbon footprint than HPS?

Yes — a by-product of running HPS lights is heat, which is desirable in winter when you would be heating the glasshouse anyway but in warm seasons its just wasted energy. When the first LED lights came about they were cheaper to run, but lacked power, so more lights were needed to achieve the same light level — but over recent years LEDs have advanced so much that they can now produce the same or even more light whilst being more efficient to run.