| 1. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Automatically adjusting light spectrum for optimal short term photosynthetic rate
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of light emitting diods (LEDs) as greenhouse illumination is increasingly common. When each LED color is individually dimmable both light spectrum and light intensity can be tuned, which opens up for optimisation of photosynthesis through automatic control of light quality and quantity. However, this requires a non-destructive biological growth signal that can be measured fast, remotely and preferably without interacting with the plants. A potential candidate signal is steady-state chlorophyll a fluorescence gain at 740 nm, defined as dF740/dq, i.e. the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by a (small) change in intensity of each individual LED color in the lamp (Ahlman et al., 2017). By automatically adjusting the spectrum, to aim for equal fluorescence gains for all LED colors (Wik et al., 2014), the instant photosynthetic rate can be optimised given a preset electric power input to the lamp. When implementing such a controller though, constraints on the spectral distribution are needed to minimise a negative impact on plant morphology.
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| 2. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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LED spectrum optimisation using steady-state fluorescence gains
- 2016
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Ingår i: Acta Horticulturae. - 0567-7572. - 9789462611092 ; 1134, s. 367-374
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Tidskriftsartikel (refereegranskat)abstract
- The use of light emitting diodes (LEDs) in greenhouses entails the possibility to control the light in a better way, since both spectrum and light intensity can be adjusted. We aim at developing a method to automatically find the optimal spectrum in terms of energy consumption and plant growth. Previous work shows that chlorophyll fluorescence (ChlF) at 740 nm strongly correlates with the photosynthetic rate (carbon dioxide uptake rate) and that the net efficiency of a LED group therefore is coupled to the fluorescence gain w.r.t. energy consumption, i.e., the slope of a curve depicting steady-state ChlF versus applied power to the LED group. In the present work we compare the fluorescence gains for six different LED types (wavelength peaks from 400 to 660 nm) and six different species: tomato, cucumber, basil, lettuce (two species) and dill. We also compare two different kinds of experiments: steadystate experiments, waiting for the fluorescence to reach a steady state at a few incident light intensities, and ramp experiments, where the light intensity is increased slowly. The ramp experiment gives essentially the same information as the steady-state experiment, but was found to slightly overestimate the gains of the blue LEDs. Being aware of this, it should be possible to initially use the faster (ramp) method in order to find the right light composition, possibly using steady-state experiments for a few LED colours to fine tune the lamp. The relative order of the fluorescence gains among the tested LED groups is similar, but not identical, for all species tested. LED660 has the highest fluorescence gain w.r.t. incident photon flux density, and LED400 and/or LED530 have the lowest. However, the important quantity is in fact the fluorescence gain w.r.t. applied electrical power. If the individual electrical efficiencies of the LEDs change the most efficient power split on the different LEDs might change.
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| 3. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Light spectrum optimization for plant growth using biological feedback
- 2018
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Ingår i: EasyChair Preprints. - : EasyChair. - 2516-2314.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The use of light emitting diods (LEDs) as greenhouse illumination is increasingly common. When each LED color is individually dimmable both light spectrum and light intensity can be tuned, which opens up for optimisation of photosynthesis through automatic control of light quality and quantity. However, this requires a non-destructive biological growth signal that can be measured fast, remotely and preferably without interacting with the plants. A potential candidate signal is steady-state chlorophyll a fluorescence gain at 740 nm, defined as dF740/dq, i.e. the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by a (small) change in intensity of each individual LED color in the lamp (Ahlman et al., 2017). By automatically adjusting the spectrum, to aim for equal fluorescence gains for all LED colors (Wik et al., 2014), the instant photosynthetic rate can be optimised given a preset electric power input to the lamp. When implementing such a controller though, constraints on the spectral distribution are needed to minimise a negative impact on plant morphology. In this study measurements were conducted (on cucumber and lettuce) under different background light, and at each setting excitation signals were sequentially added by each of six different LED colors (peak wavelength at 400, 420, 450, 530, 630 and 660 nm). The corresponding changes in steady-state fluorescence were measured with a spectrometer and the fluorescence gain (dF740/dq) was calculated for each LED color and at each background light setting. These fluorescence gains were compared in order to evaluate the different LEDs' relative effect on photosynthesis under each of the different background light settings.
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| 4. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Stress Detection Using Proximal Sensing of Chlorophyll Fluorescence on the Canopy Level
- 2021
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Ingår i: AgriEngineering. - : MDPI AG. - 2624-7402. ; 3:3, s. 648-668
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Tidskriftsartikel (refereegranskat)abstract
- Chlorophyll fluorescence is interesting for phenotyping applications as it is rich in biological information and can be measured remotely and non-destructively. There are several techniques for measuring and analysing this signal. However, the standard methods use rather extreme conditions, e.g., saturating light and dark adaption, which are difficult to accommodate in the field or in a greenhouse and, hence, limit their use for high-throughput phenotyping. In this article, we use a different approach, extracting plant health information from the dynamics of the chlorophyll fluorescence induced by a weak light excitation and no dark adaption, to classify plants as healthy or unhealthy. To evaluate the method, we scanned over a number of species (lettuce, lemon balm, tomato, basil, and strawberries) exposed to either abiotic stress (drought and salt) or biotic stress factors (root infection using Pythium ultimum and leaf infection using Powdery mildew Podosphaera aphanis ). Our conclusions are that, for abiotic stress, the proposed method was very successful, while, for powdery mildew, a method with spatial resolution would be desirable due to the nature of the infection, i.e., point-wise spread. Pythium infection on the roots is not visually detectable in the same way as powdery mildew; however, it affects the whole plant, making the method an interesting option for Pythium detection. However, further research is necessary to determine the limit of infection needed to detect the stress with the proposed method.
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| 5. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Using chlorophyll a fluorescence gains to optimize LED light spectrum for short term photosynthesis
- 2017
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Ingår i: Computers and Electronics in Agriculture. - : Elsevier BV. - 0168-1699. ; 142, s. 224-234
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Tidskriftsartikel (refereegranskat)abstract
- When changing from the traditional high pressure sodium (HPS) lamps to light emitting diode (LED) lamps there is a quite unexplored energy saving potential in the fact that they are far better suited for control, since both spectrum and light intensity can be adjusted. This work aims at finding a way to automatically adjust the spectrum of a LED lamp, equipped with several different types of LEDs, to maximize plant growth by feedback of a remote online measure correlated with growth.A series of experiments were conducted on basil plants in order to examine whether remotely sensed steady-state chlorophyll fluorescence (F740) can be used for this purpose, and if its derivatives (fluorescence gains) w.r.t. applied powers change relative to each other for different light intensities and spectraA strong correlation between F740 and photosynthetic rate was indeed found. However, the order (w.r.t. LED type) of the fluorescence gains was only moderately affected by the light intensities and spectra investigated. The gain was highest w.r.t. red light (630 nm), though, when taking the electrical efficiencies of individual LED types into consideration, blue LEDs (450 nm) were equally, or even more efficient than the red onesAn online controller to regulate optimal spectrum for basil appears to be unnecessary. However, the fluorescence gains could be used to adapt to changes in the efficiencies when crops and operating conditions change, or when the diodes degrade. The method also shows promise as a tool to find optimal light intensity levels as well as identifying plant stress.
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| 6. |
- Ahlman, Linnéa, 1987, et al.
(författare)
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Using Fluorescence as Control Parameter to Decide Optimal Light Spectrum for Plant Growth
- 2015
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Ingår i: Proceedings 19th Nordic Process Control Workshop, Hurtigruta, Norway, Jan 2015. ; , s. 9:1-4.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modern greenhouses having lighting systems are large consumers of electricity. In Europe alone, the lighting consumption is estimated to 150 TWh per year. High pressure sodium (HPS) lamps are still dominating and the illumination is in general controlled manually by on/off control. Changing to light emitting diodes (LED) gives the possibility of adapting the spectrum (i.e. changing the power split to diodes of different colours) and to gradually changing the intensity, which implies an energy saving potential. The optimal spectrum might depend on a number of factors, for example plant species, required characteristics and energy use effciency on the diodes.Using LEDs with different blue to red (B:R) ratios, as a supplement to sunlight, have been investigated for growing of cucumber seedling [Hernández and Kubota, 2014] and tomato seedling [Hernández and Kubota, 2012]. Their conclusion was that 100% red LED is preferred, indicating that the blue light in the sunlight is sufficient (B:R in sunlight is about 4:3 on photons=m2=s basis [ASTM, 2012].
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| 7. |
- Bånkestad, Daniel, et al.
(författare)
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Growth tracking of basil by proximal remote sensing of chlorophyll fluorescence in growth chamber and greenhouse environments
- 2016
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Ingår i: Computers and Electronics in Agriculture. - : Elsevier BV. - 0168-1699. ; 128, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing is a promising tool for plant phenotyping and precision farming, as it allows for non-invasive, fast and automated measurements of relevant plant traits with spatial and temporal resolution. The simplest and most used remote sensing application in the field is to use reflectance vegetation indices, based on the optical properties of chlorophyll, as indicators of variables of interest. However, the applicability is limited by their sensitivity to environmental conditions and canopy structure. Another remotely sensed signal related to chlorophyll is chlorophyll fluorescence. Compared to reflectance it is plant specific and directly linked to plant physiological processes; but it is also weak, which complicates its use for in-field applications. This study evaluates the performance of an active proximal remote sensing system utilizing the chlorophyll fluorescence ratio method, measuring the ratio of red fluorescence to far-red fluorescence (termed SFR), for the assessment of growth and biomass as an alternative or complement to reflectance vegetation indices. Basil plants were subject to chlorophyll fluorescence and weight measurements periodically throughout commercial growth cycles, both in a laboratory and commercial greenhouse environment. In the laboratory, SFR showed a strong linear relationship with dry weight on logarithmic scales. Further characterization of the method indicated that it is independent of background light and the same growth dynamics is obtained irrespective of point in time during chlorophyll fluorescence induction. The same trend that was observed in the laboratory was also observed in the greenhouse, but varying background light from the sun and from supplemental lighting added complexity that needs to be addressed in further studies. To our knowledge, the strong link between SFR and biomass, both in a closed environment and greenhouse setting, has not so clearly been demonstrated on canopy level before. Owing to the simplicity of the method, being relatively cheap and fast, it has potential for commercial applications.
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| 8. |
- Carstensen, Anna-Maria, 1982, et al.
(författare)
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Exploring the dynamics of remotely detected fluorescence transients from basil as a potential feedback for lighting control in greenhouses
- 2016
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Ingår i: Acta Horticulturae. - 0567-7572. - 9789462611092 ; 1134, s. 375-383
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Tidskriftsartikel (refereegranskat)abstract
- Optimizing artificial lighting control in industrial scale greenhouses has a potential for increased crop yields, energy savings and production timing. One possible component in controlling greenhouse lighting is continuous and accurate measurement of plant photosynthetic performance. A widely used tool for measuring photosynthetic performance non-invasively is chlorophyll fluorescence. For the purpose of automatic control, remote sensing of fluorescence is favourable, since it provides an aggregated measure for a large canopy area. However, adaptation of traditional fluorescence methodologies to remote sensing is problematic since they are based on the analysis of fluorescence intensities and therefore sensitive to distance and morphology. Other problems with using traditional methods remotely in a greenhouse are a need for dark adaption and use of saturating light. This paper presents a novel concept for the detection of photosynthetic performance based on the dynamics of remotely sensed light induced fluorescence signals. The dynamics of the fluorescence signal is insensitive to distance and morphology and hence provide a good basis for remote detection of photosynthetic performance. Through experiments we have explored how the dynamics of the time-varying fluorescence signal from basil plants was affected by light intensity, light acclimation and light induced stress. This was done by first identifying a dynamic model by transient analysis and then applying frequency analysis on the model. We conclude that the capacity of basil plants to use a certain light intensity was reflected by how fast and how complex the dynamics are. These results show that an identified resonance peak frequency is a potential indicator of plants' ability to adapt to light, which could be a valuable feedback signal for lighting control in greenhouses.
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| 9. |
- Carstensen, Anna-Maria, 1982, et al.
(författare)
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Remote detection of light tolerance in Basil through frequency and transient analysis of light induced fluorescence
- 2016
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Ingår i: Computers and Electronics in Agriculture. - : Elsevier BV. - 0168-1699. ; 127, s. 289-301
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Elsevier B.V.Artificial lighting control in industrial scale greenhouses has a large potential for increased crop yields, energy savings and timing in greenhouse production. One key component in controlling greenhouse lighting is continuous and accurate measurement of plant performance. This paper presents a novel concept for remote detection of plant performance based on the dynamics of chlorophyll fluorescence (CF) signals induced by a LED-lamp. The dynamic properties of the CF is studied through fitting a linear dynamic model to CF data. The hypothesis is that changes in photochemistry affects the fluorescence dynamics and can therefore be detected as changes in the model parameters and properties. The dynamics was studied in experiments using a sinusoidal varying light intensity (period 60 s) or step changes (step length 300 s). Experiments were performed in a controlled light environment on Basil plants acclimated to different light intensities. It is concluded that the capacity to use a certain light intensity is reflected by how fast and how complex the dynamics are. In particular, the results show that optimal model order is a potential indicator of light tolerance in plants that could be a valuable feedback signal for lighting control in greenhouses.
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| 10. |
- Lindqvist, Johan, et al.
(författare)
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Complexity of Chlorophyll Fluorescence Dynamic Response as an Indicator of Excessive Light Intensity
- 2016
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Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 49:16, s. 392-397
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Konferensbidrag (refereegranskat)abstract
- The controllability of LED lighting systems for greenhouses and plant factories offers a possibility for light induced diagnose of plant status. Here, a novel method for proximal remote detection of plant light tolerance is investigated. The method is based on an identification of a transfer function model for the measured chlorophyll fluorescence response to a small step variation in blue LED light. It is postulated that the least required model order decreases as the plants become light stressed due to saturation effects at excess light conditions. We apply this method to basil and lettuce plants under different background light intensities, and the results are compared to measured effective quantum yield (y(II)), relative electron transport rate through PSII (ETR(II)) and non-photochemical quenching (NPQ), all reflecting the photosynthetic performance. For both species it is indeed found that the required model order decreases with increasing background light intensity at the same time as the measured reference parameters indicates a decreased photosynthetic efficiency. It is suggested that the light intensity should be such that the chlorophyll fluorescence response requires a model order of 3 or higher to avoid ineffective irradiation of the plants.
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