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.
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.
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.
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.
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.
The Maya Pro has had the optical bench realigned to optimize performance in UV-B region of the spectrum. Also the aperture has been replaced with a new smaller custom aperture. From the figures sent by the Ocean Optics people, performance seems to have been improved significantly. Our Maya Pro is on its way to Helsinki. Of course, Lasse Ylianttila will have to recalibrate it before it can be used.
The people from Ocean Optics have been very helpful and have offered to check our Maya Pro and re-align the optics to try to improve its performance. I should note that the current performance is within specifications, we are just trying to tune the spectrometer to perform at its very best in the UV-B region. So after the end of summer campaign the Maya Pro will be sent to Ocean Optics.
We fetched the Maya from STUK two days ago. Performance for measuring effective UV doses is not as good as we had expected. We may have to send it back to Ocean Optics for checking… It is usable for doses if one is very careful, and very good for measuring unweighted UV and visible spectral irradiances. It should be very good for its main intended use, measuring spectral irradiance in plant canopies.