Mikkels Rhododendron ...: Led Plantelys

Artikkel tidliger bragt i RhodoNyt 4-2012

Noter om dyrkning af Rhododendron under LED-vækstlys.

”En glad amatørs pseudovidenskabelige research”

Min interesse for emnet startede, da jeg i radioen hørte, at forskere i Århus havde dyrket grønsager uden brug af andet lys end LED-lys (= light emitting diode). Vi kender efterhånden LED-lys fra mange områder i hverdagen. Hvorfor er det interessant? Fordi energiforbruget ved LED-lys er langt mindre end ved andre former for kunstige lyskilder. Samtidig er levetiden længere, efter sigende helt op til 50.000 timer. Det er væsentligt længere end lysstofrøret, og anskaffelsesprisen er efterhånden på et rimeligt niveau. Tænk hvis man kan mere end halvere sin udgift til kunstlys!

Planternes stofskifte, fotosyntesen, er betinget af følgende elementer:

1) Vand (H2O) og næringssalte som er i vandet eller tilsættes som gødning

2) Kuldioxid fra luften (CO2), f.eks. i form af vores udåndingsluft. Dette bekræfter vigtigheden af, at vi snakker med vore små kæledægger

3) Sollys, evt. kunstlys fra lysstofrør eller LED

Hvis disse betingelser er opfyldt i rette forhold, dannes der glukose (sukker), som er det ”protein”, der er basis for plantevæksten. Som en bonus for os afgiver planterne ilt gennem bitte små spalteåbninger på undersiden af bladene. Gennem de samme åbninger optager planterne CO2 fra luften. Spalteåbningerne er også de organer, der regulerer fordampningen fra bladene, den såkaldte transpiration.

Når vi Rhodo-dyrkere i den nordlige del af Europa i løbet at efteråret og vinteren starter vores prikle- eller spirekasser, er vi afhængige af kunstlys, da der simpelthen er for lidt sollys til at opretholde fotosyntesen. Jeg må skynde mig at sige, at det kan lade sig gøre uden brug af kunstlys. Men for den optimale løsning kræves ekstra lys. Gert Forum Petersen lavede i sin tid en samlemappeside om brugen af kunstlys, baseret på lysstofrør. Der kan man blandt andet læse om de lysfrekvenser, som planterne bruger til fotosyntesen. Dagslyset består af et spektrum af forskellige bølgelængder, fra kortbølget violet-blåt til langbølget rødt. Ikke alle bølgelængder er essentielle for plantevækst. Især den røde og blå del af spektret har betydning. Lysets bølgelængder måles i nanometer (nm). Rødt lys (620-720 nm) driver den primære fotosyntese og fremmer blomstring og frøsætning. Blåt lys (400-450 nm) fremmer primært den vegetative vækst, og hindrer planterne i at strække sig. Blåt lys giver altså kompakte planter. Det skal dog understreges, at den optimale lysblanding varierer alt efter planteart.

De lysstofrør vi hidtil med stor succes har anvendt, afgiver også lys af bølgelængder, som planterne ikke har brug for. LED-lys giver os mulighed for at selektere og sammensætte de frekvensområder, som er vigtige for plantevækst. Forskningen tyder på, at den ideelle balance er 92 % røde dioder og 8 % blå. Dette er en gennemsnitsbetragtning, som varierer alt efter de plantearter, der dyrkes. Optimalfordelingen for rhododendron er ikke tilgængelig på nettet og varierer formentlig fra art til art. Det er her jeg som den nysgerrige amatør er begyndt at prøve mig frem.( Et par timers blåt lys, fra morgenstunden, inden man slår over i et rødt eller blandet rødt og blåt lys, øger planternes optagelse af CO₂yderligere)

Jeg startede med at anskaffe et par 7-Watt LED-pærer, indeholdende 7 lyskilder a` 1 Watt fordelt på 4 røde (620 nm) og 3 blå (460 nm). Dette lys blev anvendt til den ene af 2 ens frøportioner. Den anden frøportion blev belyst af et 18 Watts lysstofrør farve 83. Lyskildens højde over gromediet blev justeret, så lysstyrken målt i Lumen var ens for begge bede. Forsøget var i gang!

Mine første iagttagelser tyder på, at spiringen under LED-lyset er hurtigere og bedre. Dog fik planterne rødlige blade, hvilket kunne tyde på dårlig rodudvikling. Ved eftersyn så rødderne dog fine ud. Faktisk var de langt bedre udviklet end på planterne under lysstofrøret. Nu hvor planterne er priklet om, bliver det spændende at følge den videre vækst.

Mine kælderforsøg fortsætter, og jeg skal også afprøve LED-lys på både stiklinger og podninger.

Jeg vil også arbejde videre med sammensætningen af lyset. I Tyskland (via nettet) har jeg købt LED lamper med 165 røde, og 65 blå dioder, på hver 0,06 Watt. Jeg har også et par hjemmelavede lamper, liggende på arbejdsbordet. Det giver uendelig mange variationsmuligheder når man opbygger sine egne LED-lamper.

Fakta i denne notits stammer fra div. artikler på internettet. Det er stadig her, den største viden ligger.

OBS!
Jeg er opmærksom på at LUX ikke er korrekt måleenhed for planter. Mit budget afholder mig fra at købe optimalt måleudstyr.

Mikke Jørgensen

An amateur’s research on the use of LED lights in rhododendron propagation.

Mikkel Jørgensen

Hvidovre, Denmark

(modified from the RhodoNyt 2012 (4), the magazine of the Danish ARS Chapter; written in Danish and translated by the author)

My interest in this subject started when I heard on the radio that researchers in Aarhus, Denmark, had grown vegetables without the use of natural lightning, using only LED (light emitting diode) light. LED lights are now commonly used in many ways in daily life, and this is interesting because energy consumption by LED lights is much less than with other forms of artificial light. Their lifetime is also longer, reportedly up to 50,000 hours, significantly longer than fluorescent tubes. Finally, their purchase price is now at a reasonable level, allowing a reduction of more than halve the expense for artificial lighting!

Plant metabolism, i.e., photosynthesis, is subject to the following elements:
1) water, and nutrients which are added as fertilizer;
2) carbon dioxide from the air, such as is produced from of our breath, confirming the importance of the need to talk to our little darlings; and
3) light, from either the sun or if necessary, artificial light from incandescent, fluorescent or LED lights.
If these elements are provided in the right combination, glucose is formed, the energy source for plant growth. As a bonus for us, plants release oxygen as well!

When rhodo growers in northern Europe start plants during the fall and winter in our our prickle or germination boxes, we typically utilise artificial light, as there simply is not enough sunlight to sustain optimal photosynthesis then. I must hasten to say that propagation can be done without the use of artificial light but for optimal growth, extra light is required. Gert Forum Petersen, a former member of Danish chapter and an ARS Silver Medal Awardee, discussed.

the use of artificial light, based on fluorescent lamps, and among other things, about the frequencies of light that plants use for photosynthesis. Daylight consists of a spectrum of different wavelengths, from short wavelength violet-blue to long wavelength red. Not all light wavelengths are essential for plant growth, as this is influenced by the types of pigments present in plant leaves. The red and blue parts of the spectrum are especially important. Light wavelengths are measured in nanometers (nm) and red light (620-720 nm) triggers hormones in plants that increase flowering and budding, but plants cannot grow with red light alone. Red light stimulates flowering and foliage growth, but too much red light will cause a plant to become spindly.

Blue light (400-450 nm) regulates the rate of a plant’s growth and many plant responses, including stomata opening and phototropism. A plant's moisture loss is primarily influenced by stomata and blue light controls stomata behavior (openings on or beneath the surface of the leaves that control the rate of gas and water exchange), and thus the amount of water a plant retains or expels. Phototropism is the definition of a plant's response to light; the stems grow up toward the light and the roots grow down, away from the light. Blue light thus helps determine the compactness plants, although it should be emphasized that optimum light conditions varies with plant species.

The lamps we have successfully used to date also give light in wavelengths that plants do not need. LED lights allows us to select and assemble the light wavelength ranges that are most important for plant growth. General research (http://www.easygrowled.com/Info.aspx, http://www.bbbled.com/news/41.html, http://www.newenergyresearch.net/growing_plants_with_leds.php) suggests that the ideal average balance for most plant growth is 92% red and 8% blue LEDs. However, the optimal wavelength distribution for rhododendrons is not available and probably varies from species to species. This is where, I as a curious amateur, began to test and try out various LED combinations. First I bought a pair of seven watt LED fixtures containing seven light sources of one watt each: four red (620 nm) and three blue (460 nm). This light was applied to one of two identical plantings of rhododendron seeds, with the second batch being illuminated by an 18 watt fluorescent tube (warm white 830; digit “8” is the Colour Rendering, and “30” is the colour temperature = 3000 K). Lamp height above the medium was adjusted to make a 2800 lumen brightness for both plantings. The trial was in progress, and the results after five months are reported here!

My initial observations suggested that germination with LED lights was faster and better. However, given the seedling’s reddish leaves, there was perhaps too low a light intensity. The roots looked fine and were more developed than with the the plants under fluorescent light. The plants have now been transferred into growing medium, and I am following further growth characteristics.

I will also be testing the LED lights on both cuttings and graftings, and will experiment further on the desirable composition of the light. I have recently bought LED light fixtures with 165 red and 65 blue LEDs, each of 0.06 watt. I also have a couple of homemade lamps, and there are endless variation possibilities when building your own LED fixtures. My newest creations are made with 30 one-watt diodes: 20 one-watt 660 nm reds, four one-watt 610-630 nm reds, and six one-watt 450-455 nm royal blues. The diodes are mounted on a 0.5 m² sheet of aluminum to prevent overheating. My hope is to achieve a 40-50% power saving.