The power and po­ten­tial of light – the LED way

LED light tech­nol­ogy is chang­ing glasshouse op­er­a­tions in many ways.

NZ Grower - - Contents - By Denise Landow

All LED light given to crops can be con­verted into growth – that’s what in­ter­na­tional light­ing ex­perts told tomato grow­ers at an open day in Au­gust.

Grow­ers and hor­ti­cul­tural in­dus­try rep­re­sen­ta­tives came from around the coun­try to learn about new ways that LED light­ing is chang­ing glasshouse op­er­a­tions around the world. It’s rare that they gather to­gether in such a mass scale apart from an­nual con­fer­ences and na­tional meet­ings, but they did so to see first-hand new in­no­va­tive light­ing tech­nol­ogy re­cently in­stalled at Gourmet Mokai tomato glasshouse op­er­a­tion, just north of Taupo. This is the first in­stal­la­tion of LED top­light­ing and LED in­terlight­ing in a New Zealand com­mer­cial hor­ti­cul­tural set­ting.

The day pro­vided an op­por­tu­nity for grow­ers to lis­ten, learn, ask some hard questions, look at a LED green­house op­er­a­tion – and it also got them think­ing about how such new tech­nol­ogy could ben­e­fit their op­er­a­tions.

It was or­gan­ised by in­ter­na­tional in­dus­try gi­ant, Dutch-based light­ing and elec­tri­cal man­u­fac­turer, Sig­nify (for­merly known as Philips Light­ing). The group’s plant spe­cial­ist for high­wire crops and soft fruits, Piet Hein van Baar, took the grow­ers through a short his­tory of LED tri­als to date and pro­vided an over­view of the practical and tech­ni­cal as­pects of in­stalling and run­ning LEDs in a com­mer­cial glasshouse set­ting.

With in­sights from his team’s hard­earned ex­pe­ri­ence and hu­mour, Piet, cap­ti­vated the au­di­ence. This in­cluded a one-liner that made laugh­ter rip­ple through the au­di­ence, “This is no fake news.”

Sig­nify’s Aus­tralian-based key ac­count man­ager for Philips hor­ti­cul­tural light­ing, Aart Slobbe, dis­cussed his work in de­vel­op­ing in­di­vid­u­al­ly­tai­lored sys­tems help­ing grow­ers achieve bet­ter re­sults. The au­di­ence heard from NZ Gourmet’s pro­duc­tion

di­rec­tor, Pro­tected Crops, Roelf Schreuder, and Mokai on­site se­nior grower, Hans van Veen, who out­lined their ex­pe­ri­ence of in­te­grat­ing and us­ing the new tech­nol­ogy in the op­er­a­tion.

Piet said that since start­ing with LEDs 11 years ago, the com­pany has been at the fore­front of tri­als, grower part­ner­ships and new start-ups in Europe and in new city farms in the United States. Mainly Piet’s work has been with grow­ers of high wire crops like toma­toes, pep­pers, and young plants.

He said it’s one thing to make and sell light, but Sig­nify should also be able to give ad­vice about what to do with that light be­cause grow­ing with LEDs is so dif­fer­ent from us­ing con­ven­tional sources, such as high-pres­sure sodium (HPS) or solely with nat­u­ral sun lit op­er­a­tions.

It was in 2012 that the first com­mer­cial green­house in the Nether­lands started with in­terlight­ing, and in 2014 the team opened the first com­mer­cial city farm in the US and had its first in­ter­na­tional high-wire in­for­ma­tion shar­ing event.

What be­came ap­par­ent early on in the dis­cus­sion is the team had taken num­ber-crunching and an­a­lyt­ics to a high-level – there is vir­tu­ally no guess­work in­volved. But the waiver is the predictions are only as good as the raw data that in­di­vid­ual grow­ers have on hand to start with.

With the first North­ern Euro­pean op­er­a­tions, the chal­lenge was to im­prove win­ter pro­duc­tion while main­tain­ing con­sis­tent high qual­ity. One of Sig­nify’s best sto­ries so far in­volves a grower in Fin­land. This north­ern grower has a 3000m² glasshouse op­er­a­tion, where he proves toma­toes can be grown in win­ter con­di­tions of -23 °C with full LED, said Piet.

In an­other project, the com­pany is work­ing with a grower in Rus­sia who started with 25ha un­der full LED, and has re­cently de­cided to ex­tend its op­er­a­tion with 37ha this year due to high pro­duc­tion fig­ures and im­prove­ments in crop qual­ity.

Con­trol­ling your own cli­mate

Since start­ing with LEDs 11 years ago, the com­pany has been at the fore­front of tri­als, grower part­ner­ships and new start-ups in Europe and in new city farms in the United States.

LED light­ing’s trump card is mainly about en­ergy ef­fi­ciency – and with­out the dan­ger of too much ra­di­ant heat and en­ergy wastage. The abil­ity to have more con­trol over cli­mate is also an im­por­tant fac­tor.

The place­ment of the LED has much to do with over­all canopy suc­cess. Tra­di­tional high-wire glasshouse grow­ers use top light which fades away as it pen­e­trates the lower struc­tures.

High-wire crops face an added chal­lenge be­cause their abun­dant crop canopy lim­its over­head light from reach­ing the part of the crop that needs the light most. In fact, over­head light­ing pro­vided by top light­ing mod­ules usu­ally pen­e­trate to only about 75cm below the crop canopy.

Tri­als proved that plac­ing LEDs in the mid­dle of the crop was the an­swer. For ex­am­ple, plac­ing LEDs in a hor­i­zon­tal strip in be­tween the third and fourth truss of a tomato crop, adds light to ar­eas which usu­ally suf­fer from light star­va­tion. This is called in­terlight­ing.>

Plac­ing LED light­ing within the canopy di­rects and fo­cuses growth stim­u­lat­ing light on the most vi­tal part of the crop. By ap­ply­ing a side­ways light dis­tri­bu­tion pat­tern, the leaves can more ef­fi­ciently trans­form the light into grow­ing more yield.

LEDs have sig­nif­i­cantly more light power com­pared to HPS per elec­tri­cal watt, and far less ra­di­a­tion heat com­pared with HPS and sun­light. LED light can be far more ex­act­ing us­ing the colour spec­trum that af­fects pho­to­syn­the­sis.

A light recipe

All plants have dif­fer­ent light needs. Philips GreenPower LED light­ing of­fers grow­ers a choice of ‘light recipes’ which are ded­i­cated com­bi­na­tions of spec­trum, in­ten­sity, tim­ing, uni­for­mity and po­si­tion­ing within the glasshouse en­vi­ron­ment. The com­pany has de­vel­oped these tools over many years of co-op­er­a­tion with city farm­ers, green­house grow­ers, univer­si­ties, and re­search or­gan­i­sa­tions.

The Philips LED mod­ules come in mul­ti­ple spec­tral ver­sions, which have com­bi­na­tions of two to four light colours. Dif­fer­ent light colours can have dif­fer­ent ef­fects on crops. But com­monly deep red is the most ef­fi­cient for pho­to­syn­the­sis, veg­e­ta­tive re­pro­duc­tion and stim­u­la­tion of shoot de­vel­op­ment. Far red has a pos­i­tive ef­fect on gen­er­a­tive prop­er­ties, flower for­ma­tion and root­ing. Blue has pos­i­tive ef­fects on com­pact­ness and hard­en­ing. White is a work­ing light with the full spec­trum of colours.

LED pro­vides a plat­form in which grow­ers can play with the light spec­trum and pick the spec­trum that’s best for their crop. In­di­vid­ual light recipes make it pos­si­ble to steer spe­cific plant char­ac­ter­is­tics and to suit

dif­fer­ent plant va­ri­eties such as com­pact­ness, colour in­ten­sity and branch de­vel­op­ment, re­sult­ing in op­ti­mised crop yield and qual­ity.

Se­lect­ing from the spec­trum

In white light, plants are seen as green be­cause the leaves don’t ab­sorb green light, but partly re­flect it.

Piet chal­lenged the au­di­ence’s think­ing.

“The spec­trum of sun­light has ev­ery­thing; UV, red, green, blue – all to­gether it makes white,” he said.

“But do plants use ev­ery­thing in the same way? Is all that spec­trum of light needed to grow your plant?

“HPS has many ranges of blue, green, and yel­low but not that much red light. But if you look at plants, in par­tic­u­lar tomato plants, they need blue light to open the stom­ata and get the right mor­phol­ogy into the plant, and red light is mainly for pho­to­syn­the­sis. Red light is the most im­por­tant thing for grow­ing. That’s one of the rea­sons we put so much red light into these mod­ules.

“If you see the green­house at night with the red and blue lights, the plants ap­pear to­tally black but they would still be grow­ing.”

Adding in­terlight­ing into the canopy cre­ates more pho­to­syn­the­sis – par­tic­u­larly around the bot­tom of the crop, said Piet.

With LED – all the light that you give to the crop can be con­verted into growth, of­fer­ing grow­ers the po­ten­tial to have higher plant den­si­ties and fruit weights, Piet said.

Work­ing out in­di­vid­ual recipes starts with form­ing a num­bers­based growth plan. Sig­nify uses the mea­sure­ment of ‘mi­cro­mol’ for cal­cu­la­tion.Rather than a blunt in­stru­ment of us­ing to­tal pro­duc­tion, the bet­ter and fairer way to judge how good a grower is do­ing, is by us­ing the cal­cu­la­tion of grams per mol of light.

“We start with a ref­er­ence with day­light only be­cause we want to know how good you are as a grower,” he said.

“From here we can cal­cu­late how many grams per mol of light a grower pro­duces. We al­ways cal­cu­late ev­ery­thing back to grams per mol, this is also a way we are able to com­pare dif­fer­ent grow­ers. If you only look at the pro­duc­tion kilo­gram per square me­tre it’s not fair be­cause grow­ers have dif­fer­ent light lev­els in mi­cro­moles/m²/s.” Grower questions

At ques­tion time, one of the grow­ers asked about the nutri­tional value or taste dif­fer­ences us­ing LED.

All plants have dif­fer­ent light needs. Philips GreenPower LED light­ing of­fers grow­ers a choice of ‘light recipes' which are ded­i­cated com­bi­na­tions of spec­trum, in­ten­sity, tim­ing, uni­for­mity and po­si­tion­ing within the glasshouse en­vi­ron­ment.

Piet an­swered by say­ing, “we can­not say if you add LED that you’ll get bet­ter taste. Taste is cre­ated by the va­ri­ety and the

grower, and how grow­ers treat their crops, how­ever, we’ve seen with LED the green part of the trusses are get­ting stronger”.

An­other grower said that in New Zealand, there aren’t many grow­ers with HPS sys­tems, and most Kiwi op­er­a­tions have no sup­ple­men­tary light­ing - so that start­ing point would be day­lightonly mod­els. So would the im­pli­ca­tions of in­terlight­ing and top­light­ing with LEDs be more sig­nif­i­cant?

“What you have to keep in mind in New Zealand is that you do have high light lev­els, even early in the win­ter time,” Piet said.

“But when your light starts de­creas­ing also the ra­di­a­tion heat from the sun starts de­creas­ing.”

Roelf said with New Zealand’s cli­mate, when the sun comes out, it’s pow­er­ful and heats the green­house straight away.

“You want to have heat in the bot­tom of your crop to get quick ripen­ing of fruit, while keep­ing your head as cool as pos­si­ble. When we thought about putting in HPS it would mean too much heat at the top of the crop. Go­ing through that ex­er­cise and see­ing the ef­fect of the heat, we backed off HPS and started talk­ing to Sig­nify again about their Philips LEDs.

“With the light at the top of the crop, it makes you look at the crop in a dif­fer­ent way – LED works well and it was a good de­ci­sion for us not to have HPS in here.”

Pur­chas­ing power

Power con­sump­tion is an­other im­por­tant fac­tor. HPS uses a lot more power, and that gap be­tween the two lev­els in power use, means the Mokai op­er­a­tion will earn the pur­chase price dif­fer­ence back in five years’ time on the power sav­ings, Roelf said.

The LED equip­ment is pro­jected to last at least 35,000 hours, re­sult­ing in lower main­te­nance and run­ning costs. Sig­nify spec­i­fies 35,000 hours, and even at 35,000 hours they still have 90 per­cent of the orig­i­nal out­put that was orig­i­nally in­stalled. Re­search shows mod­ules in op­er­a­tion for seven years are still at 98 per­cent to­tal ef­fi­ciency, Piet said. An­other ques­tion was asked about the CO2 en­rich­ment - at what point is ex­tra light­ing be­ing negated by lack of CO2?

“You want to have heat in the bot­tom of your crop to get quick ripen­ing of fruit, while keep­ing your head as cool as pos­si­ble.”

Piet said the an­swer was sim­ple; the mo­ment the plant gets light, it needs CO2 but when light­ing is halted dur­ing the night, then pho­to­syn­the­sis lev­els are ex­tremely low.

“I have two rules when LED is switched on. You have to put CO2 into your crop and heat your green­house. Light­ing dur­ing the night with LED with­out high tem­per­a­ture can be likened to a mu­seum – the plants will look ex­cel­lent but they don’t grow.”

An­other point was made about over­sat­u­rat­ing plants from the top with light. Sat­u­ra­tion point for top­light­ing has been found to be around 425450 mi­cro­mols/m²/s of light. Af­ter 450 mi­cro­mols/m²/s, adding more light is vir­tu­ally no use. Plants re­spond best be­tween 250-450 mi­cro­mols/m²/s.

“With LED in­terlight­ing we bring PAR light into the canopy of the crop and there we have our ‘X’ fac­tor,” Piet said.

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