The Earth is not flat. Are plants and plant canopies flat?

Cosine diffuser as used to measure irradiance. Off-the-shelf D7-H type from Bentham Instruments.

The problem

Irradiance or spectral irradiance on a horizontal plane is normally used to quantify energy or photons available for photosynthesis. Similar measurements of irradiance in narrow bands of the spectrum or spectral irradiance measurements are used to characterize radiation features perceived by plant through photoreceptors. Continue reading “The Earth is not flat. Are plants and plant canopies flat?”

Brighter times for our growth chambers

The latest LEDs from Nichia and other suppliers are game changers. I designed a replacement light source for our Aralab Fitoclima 1200 growth chambers and Nikolai Belevich (Biotechnology Institute) assembled a prototype before the start of the pandemic. This post was written time ago, but I am publishing it now that the final design of the light sources is ready for use after extensive testing. Nikolai Belevich also assembled the six light boxes for three growth chambers based on the final design, to which he also contributed.

In this post I briefly describe the prototype and some of the steps that led to the final design. I also discuss how the latest LED components, icnluding some specifically designed for horticulture, have qualitatively changed lighting possibilities in growth chambers and rooms.

Continue reading “Brighter times for our growth chambers”

Visible and UV-A radiation in greenhouses

Different cladding materials transmit different amounts of ultraviolet radiation, and we cannot see this with our eyes. The following UVA photographs give an idea of how different parts of the same greenhouse may differ without we being able to see it.

Roof of a greenhouse seen in visible light.
Roof of a greenhouse seen in UVA radiation.

Light distribution in greenhouses is not spatially even, neither irradiance (“intensity”) nor spectrum (colour) are uniform in space. Ventilation openings, supporting structures, differences in cladding materials and shade screens affect both. To some extent these patches move as the position of the sun moves, but not necessarily enough to even-out light conditions over the whole area of a greenhouse compartment. Other factors affecting the amount of radiation transmitted are the cleanliness of the cladding surface, and the angle between incoming direct solar radiation and the surface of the cladding. An example of how closed and open roof vents affect illumination.  Two visible light photographs taken only a few minutes apart under fully clear sky conditions around 2 pm solar time.

Visible light closed vents and open shade screen.
Visible, open vents and closed shade screen.

Paired photographs in UV-A radiation.

UVA radiation, closed vents and open shade screen.
UVA radiation, open vents and closed shade screen.

This highlights why design of experiments, and correct randomisation in space and time are crucial when using greenhouses in research or at early stages of crop breeding.

Our new growth chambers

aralab growth chamber with Valoya B50 luminaires.

Two new growth chambers have been delivered some days ago and were switched-on yesterday. We have been longing for good chambers for some time, in particular chambers with a rather small size but capable of achieving high irradiance. Our chambers were supplied by Aralab with a series customizations that will make them very well suited for our research in photobiology: LED lighting using a modular design, at the moment with Valoya B50 fixtures “AP67”, but user exchangeable by other types lighting modules. Dimming is possible down to 10% on each of three “channels” allowing a range of irradiance at 20 cm from the enclosed lamp canopy ranging from 40 μmol m-2 s-1 to 1100 μmol m-2 s-1, being possible to set steady-state irradiance in steps as small as approximately 5 μmol m-2 s-1, and to program stepless irradiance ramps. Being the design modular, although currently all our B50 modules have the same spectral emission characteristics, will allow us to mix and match B50 modules as needed and control the mixing ratio between three types of spectra if desired. The main idea of this design is to be able to achieve at reasonable cost a system that will allows us to grow plants under different light spectra without sacrificing the ability to achieve a high irradiance under each of them. Another important design point for our research is that the “window” of the lamp canopies can be easily exchanged, and given the rather low downward thermal radiation emission of the LED fixtures, plastic sheeting can be used. This will allow when needed in the future to use coloured filters, or UV-radiation transmitting acrylic.

The use of LEDs together with temperature-dependent ventilation of the lamp canopies should result in irradiance in the plant growing area to remain, at a given lamp control setting almost independent of the temperature conditions used in the experiment without need for a feedback control system. This is a fundamental difference with fluorescent tubes located in the plant growth space, for which the light output is extremely temperature and air movement dependent, output decreasing with decreasing temperature.

The chambers are specified to reach a few degrees below freezing in darkness and +5 C with lights on. Humidity control is possible as well as CO2 concentration control, within the range 200 to 1500 μmol mol-1.

Our aralab chambers

Our chambers are customized Aralab FITOCLIMA D1200 PLLH. The in built controller and the remote access software seems well thought out based on our experience of the last two days of on-site training. More information is available at Aralab’s web site.

I will post in coming weeks some test results and further impressions on these new chambers. Meanwhile I would like to thank the Aralab people for their willingness to listen to our wishes and work along with us in finding the best possible customization for our research needs. I should mention that I have been myself repairing and modifying growth chambers in the past, even designing and assembling simple electronic control systems for chambers already while working on my M.Sc. thesis, long ago and far away.

Software for solar and lamp radiation calculations and acquisition

As part of my participation in the COST Action UV4growth I have been working on an R packages for analysing and acquiring spectral data using the R system for statistics. They are described and can be downloaded from the blog of the Technical Group 1 (TG1) of the COST Action. The package UVcalc is at version 1.2.0 and will be ready for wide use after a few days of additional testing. There are another two packages under development, but not yet ready for release: one of them is for applying advanced correction algorithms as developed by Lasse Ylianttila from STUK for improving the performance of array spectrometers in the UV region of the spectrum. Another package under development will allow the control and acquisition of spectral data from Ocean Optics spectrometers directly from within R. If you are willing to test or use any of these packages, or even help with the coding, please, contact me. The packages will be released under GPL licence and at the moment are in a Git repository hosted at Bitbucket. The UVcalc repository is already public, the others are private.

High power LEDs

There are now really high power LED modules available at reasonable prices. One manufacturer from Taiwan,  Huey Jann Electronics Industries, has available 100 watt LED modules. They are approximately 5 by 5 cm square and emit as much light as a 1000 W quartz halogen lamp. I have ordered a few 30 W and 100 W LED modules to use in gas-exchange measurements. I ordered them through Kruse Lighting Solutions. (26/11: The LEDs arrived.)


The Arduino is a controller/miniature computer on a small board. “Shields” can be attached attached to add funtionality. They are cheap at around 20-25 €. I have ordered one Arduino UNO and a logger shield, and a few extra parts.  I am planning to use one of these to control the dimming of lamps and another one to build a prototype UV-logger to measure UV in canopies.

UV-B, UV-A and blue light sensors ordered

I have ordered one erythemal, one UV-A and one blue light sensor. These are silicon carbide photodiodes with a built-in amplifier. They are made by sglux in Germany. They are small and relatively cheap. The UV ones are inherently visible blind.