CONSTRUCTION OF GREENHOUSE

CONSTRUCTION OF GREENHOUSE

1. BIRSA AGRICULTURAL UNIVERSITY
Protected Cultivation and Secondary
Agriculture
LECTURE 10: CONSTRUCTION OF GREENHOUSE
BY
DR. PRAMOD RAI
DEPARTMENT OF AGRICULTURAL ENGINEERING

2. Materials for construction of greenhouse (GH)
Structurematerials
Claddingmaterials
Gadgetforenvironmentalcontrol

3. GH type based on cost of construction or
technology
Low cost or low tech GH
Medium cost or medium tech GH
High cost or hi-tech GH

4. Structu
re &
Glazin
g
Environment Culture
method
Expected
yieldof
tomato
(kg/m
2
/yr)
Investme
nt cost
(Rs./m
2
)
Canopy Root
Bambo
o or
Wood
Single
layer
Passive
cooling
(roof and
side wall
vents)
No
heating
Soil
Drip
irrigation
with
manual
control
Med-
high
wire
10 –20300-500
Low cost or low tech GH

5. Structure
&
Glazing
Environment Culture
method
Expected
yield of
tomato
(kg/m
2
/yr)
Investmen
t cost
(Rs./m
2
)
Canopy Root
Steel
frame
Double
PE film or
rigid
plastic
Passive/A
ctive
cooling
(vents+pa
d/fan)
With or
without
air heating
Basic
level of
computer
control
Soil or
soiless
substrate
Drip
irrigation
Some
control
High
wire
culture
Longer
season
Usually
computer
ized
fertigatio
n
25 –50500 –1500
Medium cost or medium tech GH

6. Structure
&
Glazing
Environment Culture
method
Expected
yield of
tomato
(kg/m
2
/yr)
Investment
cost
(Rs./m
2
)
Canopy Root
Steel or
Aluminu
m frame
Glass,
polyethyle
ne or
Polycarbo
nate
Forced
ventilation
+
evaporativ
e cooling +
hot water
pipe
heating +
CO
2
enrichment
+ shading
(light) +
energy
blanket
Soilless
substrate
Drip
irrigation
with full
automated
control
(EC
control
according
to light
intensity)
High wire
culture
Fully
computeri
zed
fertigation
Recirculat
ion
Hydroponi
cs
50 –75
More than
1500
High cost or high tech GH

7. Greenhouse Construction Materials
Lowcostgreenhouse
S. N.Materials Purpose Photographs
StructuralMaterials
1.Bamboo Used forstructural
componentslikecolumn,
beam,truss,etc.
2.Wood Used forstructural
componentslikecolumn,
beam,truss,etc.
3.ConcretepillarsUsedforcolumnonly.

8. S. N.Materials Purpose Photographs
CladdingMaterials
1.UV
stabilized
polyfilm
UsedforcladdingGHto
createfavorablemicro
climateinsidethestructure.
2.ShadenetUsedforreducingthesolar
radiationinsideGH.
3.Insectproof
net
Usedascladdingmaterialto
checktheentryofinsects
insidethestructure.
4.Profilewith
springlock
Tofastenthecovering
materialswithstructure.
.

9. S. N.Materials Purpose Photographs
Miscellaneous
1.Wire Tofastenthestructural
memberswitheachother.
2.Coal tar Forpreservationofbamboo
andwoodfromdecay.
3.PVCpipePutthebottomofthe
bamboopoleinsidethepipe
andthenputinthesoil.It
willpreventthebamboo
fromtermiteattackandother
decay.
4.Waste
plastic
mulch
Wrapthebottomofthe
bamboopolewiththewaste
plastictopreventdecaydue
tomoisture.
.

10. Greenhouse Construction Materials
Mediumcostgreenhouse
S. N.Materials Purpose Photographs
StructuralMaterials
1.GIPipe Used for structural
componentslikecolumn,
beam,truss,etc.
2.Gutter Todrainouttherainwater
fromtheroofofthe
greenhouse.
3.GIcable Tosupporttheshadenetor
aluminatesinthegreenhouse

11. S. N.Materials Purpose Photographs
CladdingMaterials
1.Multilayer
UV
stabilized
polyfilm
UsedforcladdingGHto
createfavorablemicro
climateinsidethestructure.
2.Different
colorShade
net
Usedforreducingthesolar
radiationinsideGH.
3.Insectproof
net
Usedascladdingmaterialto
checktheentryofinsects
insidethestructure.
4.Profilewith
springlock
Tofastenthecladding
materialswithstructure.
.

12. S. N.Materials Purpose Photographs
Gadgetsforenvironmentcontrol
1.Exhaustfan
withpad
Todecreasetheair
temperatureinGHby
evaporativecooling.
2.Foggers Toincreasethehumidityand
decreasetheairtemperature
insidetheGH.
3.Misters Toincreasethehumidity
withinthemicroclimateof
theplants.
..

13. S. N.Materials Purpose Photographs
Miscellaneous
1.Nut and
bolts
Tofastenthestructural
memberswitheachother.
2.Thermal
screen
Thermalscreensallowto
controllight&temperature
moreprecisely,Itisdesigned
tokeeptheheatinsidethe
structure.
.

14. Greenhouse Construction Materials
Highcostgreenhouse
S. N.Materials Purpose Photographs
StructuralMaterials
1.GIPipe Used as structural
componentslikecolumn,
beam,truss,etc.
2.Gutter Todrainouttherainwater
fromtheroofoftheGH.
3.GIcable Tosupporttheshadenetor
aluminatesintheGH.

15. S. N.Materials Purpose Photographs
CladdingMaterials
1.Multilayer
UVstabilized
polyfilm
UsedforcladdingGHto
createfavorablemicro
climateinsidethestructure.
2.Polycarbonate
sheet
UsedforcladdingGH.
3.Glass UsedforcladdingGH.
4.Different
colorShade
net
Usedforreducingthesolar
radiationinsideGH.
.

16. S. N.Materials Purpose Photographs
CladdingMaterials
5.Insectproof
net
Usedascladdingmaterialto
checktheentryofinsects
insidethestructure.
6.Profilewith
springlock
Tofastenthecovering
materialswithstructure.
7.Floor
covering
Usedforfloorcoveringto
preventfungaldevelopment.
8.Thermal
screen
Thermalscreensallowto
controllight&temperature
moreprecisely,Itisdesigned
tokeeptheheatinsidethe
structure.
.

17. S. N.Materials Purpose Photographs
Gadgetsforenvironmentcontrol:Cooling
1.Exhaustfan
withpad
Todecreasetheair
temperatureinGHby
evaporativecooling.
2.Foggers Toincreasethehumidityand
decreasetheairtemperature
insidetheGH.
3.Misters Toincreasethehumidity
withinthemicroclimateof
theplants
4.ExhaustfanPulloutthehotairfrom
insidetheGHtobringdown
thetemperature.
.

18. S.NoMaterialsPurpose Photographs
Gadgetsforenvironmentcontrol:Cooling
5.Roof
evaporative
cooling
Sprinklingofwaterontoa
surfaceoftheroofsoasto
formathinlayer.
Watertemperaturefalltothe
wetbulbtemperatureofthe
closelysurroundedair.
6.Paintingof
GH roof
with
hydrated
Calcium
oxide
Itreducesboththe
temperature&thelight
intensity.
7.ShadingnetsItwilldiffuselightrays&
reflectheat,comeeitherin
whiteorgreenandcanbe
thinnedusingpaintsolvent.
.

19. S.No Materials Purpose Photographs
Gadgetsforenvironmentcontrol:Heating
1.Unitheaters Theycanprovideuniformbench
toptemperaturesaswellasunder
thebenchtemperature.
2.CentralHeating
(hot water
system)
Steamorhotwaterisproduced,
plusaradiatingmechanisminthe
GHtodissipatetheheat.
3.CentralHeating
(steamheating
system)
4.Radiantheater
system
Theseheatersemitinfrared
radiation,whichheatobjectssuch
asplants,walksandbenches,they
willwarmtheairsurrounding
them.
.

20. S. N.Materials Purpose Photographs
Gadgetsforenvironmentcontrol:Lighting
1.HighIntensity
Discharge
lamps
It generates the
supplementallightinginthe
GH.
2.MetalHalide
lamps
Theyprovidethebest
overallspectraldistribution
ofallhorticulturallamps.
3.HighPressure
sodiumlamps
Usedforcommercial
supplementallightingin
horticulture.Theyarethe
mostefficientinthePAR
rangewiththeexceptionof
lowpressuresodiumlamps.
4.Incandescent
lamps
Theyarenotverylight
efficientandarelatively
shortlamplife,itisusually
notthemosteffective
radiationsources.
.

21. S.No Materials Purpose Photographs
Gadgetsforenvironmentcontrol:Lighting
5.Fluorescent
lamps
Itproducelightfromthe
excitationoflowpressure
mercuryvaporinamixture
ofinertgases.
Theyaremorelightefficient
thanincandescentlampsand
havemuchlongerlifespan.
Gadgets for environment control: Inside air circulation
1Axialfan Itacceleratetheair
movement insidethe
greenhousetomaintainthe
uniformtemperatureand
RH.
.

22. S. N.Materials Purpose Photographs
Gadgetsforenvironmentcontrol:CO
2enrichment
1.CO
2
generator
(Inside)
ToIncreasetheCO
2level
insidetheGHstructure.
2.CO
2
generator
(Outside)
ToIncreasetheCO
2level
insidetheGHstructure.
3.CO
2
cylinder
ToIncreasetheCO
2level
insidethegreenhouse
structure.
.

23. S. N.Materials Purpose Photographs
Gadgetsforenvironmentcontrol:Relativehumidity
1.De-
Humidifier
Todecreasethehumidity.
2.HumidifierTodecreasetheair
temperaturebyincreasing
thehumidity.
3.Foggers Toincreasethehumidityand
decreasetheairtemperature
insidetheGH.
.

24. S. N.Materials Purpose Photographs
Miscellaneous
1.Nut and
bolts
Tofastenthestructural
memberswitheachother.
.

25. S. N.Materials Purpose Photographs
Growingmedia
1.Vermi
Compost
Organicmanureforsoilless
cultivation.
2.Cocopit Organicmanureforsoilless
cultivation.
3.VermiculiteOrganicmanureforsoilless
cultivation.
4.Growing
bag
Usedforsoilless
cultivation.
.

26. Gadgets used in greenhouse (GH)

27. Temperature
Onesideregistersthemaximumtemperatureandother
siderecordsminimumtemperature.Thebendatthe
bottomofthethermometercontainsmercurywhich
movesupordownbasedontheexpansionand
contractionofalcohol.
Whenthetemperaturerises,thealcoholexpandsand
pushesthemercuryupthemaximumcolumn.Thisalso
pushesthemercurydownintheminimumcolumn.
Similarly,whenthetemperaturefalls,thealcohol
contractsandpullsthemercuryupintheminimum
columnresultinginafallofmercuryinthemaximum
column.
Thesteelindexesarelocatedonthesurfaceofmercury.
Theymovealongwiththeflowofmercuryupand
down.Whentemperaturereachesitsmaximumand
minimumlimits,themetalindexesremainattheplace.
Thishelpsinrecordingthemaximumandminimum
temperatureoftheday.
Digitalthermometersarebecomingmore
common.Theyareeasiertoread,offerremotesensing
capabilitiesinhard-to-reachareas,andsometimeshave
dataloggingcapabilities.

28. Surface Temperature
IncaseswherelargedifferencesintemperatureexistbetweenGHplantsand
surroundingsurfacessuchaswalls,glazingandfloor,theradianttemperature
ofthosesurfacescaninfluencetheeffectiveplanttemperature.
Aninfraredthermometermeasuressurfacetemperature.Thisisaline-of-sight
instrumentanddetectstheradianttemperatureofobject(s)itcansee.
Infraredthermometersemployalens
tofocustheinfraredlightemitting
fromtheobjectontoadetectorknown
asathermopile.
Thethermopileabsorbstheinfrared
radiationandturnsitintoheat.The
moreinfraredenergy,thehotterthe
thermopilegets.Thisheatisturned
intoelectricity.Theelectricityissent
toadetector,whichusesitto
determinethetemperatureofwhatever
thethermometerispointedat.

29. Humidity
Thetraditionalwaytomeasurerelativehumidityisa
two-stepprocess:Firstobtainwetbulbanddrybulb
temperatures,andthenconvertittorelativehumidity
usingapsychrometricchart.
Thedrybulbtemperatureiscommonlymeasuredwitha
standardthermometer.Thewetbulbtemperatureis
determinedfromastandardthermometermodifiedwitha
wettedfabricwickcoveringthesensorbulb.
Theadiabaticevaporationofwaterfromthethermometer
bulbandthecoolingeffectisindicatedbyawetbulb
temperaturelowerthanthedrybulbtemperatureinthe
air.
Relativehumiditycanbemeasureddirectlybyusing
hygrometer.Digitalhygrometersdeterminerelative
humiditywithsolid-statedevicesandelectronics.
Thesensorisamatrixmaterialinwhichelectrical
propertieschangeaswatermoleculesdiffuseintoorout
ofthematrixmaterialinresponsetowatervapour
content.

30. Luxmeter
Luxisameasurementoftheoverallintensityoflightwithinanenvironmentfor
anygivenareaordistancefromthesourceorluxistheamountoflightin
anenvironmentsperceivedbythehumaneye.
Inotherwords,theluxisaunitofmeasurementofbrightness,ormore
accurately,illuminance.
Aluxmeterisadeviceformeasuringbrightness.Itspecificallymeasuresthe
intensitywithwhichthebrightnessappearstothehumaneye.Thisisdifferent
thanmeasurementsoftheactuallightenergyproducedbyorreflectedfroman
objectorlightsource.
Aluxmeterworksbyusingaphotocelltocapturelight.
Themeterthenconvertsthislighttoanelectricalcurrent.In
turn,theamountofcurrentdependsonthelightthatstrokes
thephotocellorlightsensor.
Luxmetersreadtheelectricalcurrent,calculatethe
appropriatevalue,andshowsthisvalueonitsdisplay.

31. Air speed
Airspeedismeasuredwithananemometer.
Vanetypeanemometer[Suitableforairspeed(>50fpm)]
Hot-wireanemometer[Suitableforairspeed(<50fpm)]
Avanetypeanemometerismoreruggedandusuallylessexpensivethana
hot-wireanemometer.Itiswellsuitedtomeasurehighspeedair.Designs
vary,butmosthaveathreeinch-diametervanepropeller,whichstartsturning
whenthepropellerisheldinanairstream.
Inmodeminstrumentsthespeedofrotationofthe
vaneissensedandmeasuredelectronicallyand
theairspeed,whichisafunctionofthespeedof
rotationofthevane,isindicatedonameter.
Vaneanemometersdonotmeasurelowairspeeds
becausethemassofthevanerequiresafair
amountofairmovementtoinducerotation.
Vaneanemometersarenotconsideredaccurate
below50to60fpm,eventhoughthemeter
displaysavelocityattheselowairspeeds.
Vane type anemometer

32. Ahot-wireanemometerhasaveryfine,shortwire,oftenthethicknessofa
humanhair,positionedbetweentwosupportswhichincorporatesa
temperature-sensingthermistor.Thewireisheatedbyelectroniccircuitryand
airflowingoverthewirecausesitstemperaturetodecrease.
Bydetectingthistemperaturedecrease,or
byevaluatingtheamountofcurrent
suppliedtokeepthetemperatureofthe
wirefromdecreasing,theanemometer
determinesthespeedofthepassingair.
Ahotwireanemometeristheinstrument
ofchoiceforlowairspeed
measurements.Airthatisvirtuallystill
(<50fpm)existsinmanyGH,especially
awayfromventilationinletsandoutlets.
Duetotheirsmallsize,itcanbeusedin
smallplaces.
Air speed
Hot-wire anemometer

33. Portable CO
2monitor
Plantsusecarbondioxide(CO
2)inaprocesscalledphotosynthesis,GH
growersfrequentlyincreaseplantproductionthroughsupplementationof
carbondioxideintheGHenvironment.Theambientcarbondioxide
concentrationisaround350to400ppm.GrowersusuallyenrichtheGH
environmenttoalevelofaround1,000ppm.
CO
2sensorinvolvesthegasbeingpumpedordiffusedintothelighttube.
Theelectronicsthenmeasuretheabsorptionofthecharacteristicwavelength
oflight.Theamountoflightabsorptionisconvertedintoanelectricaloutput
thatprovidesapartspermillion(ppm)or%volumemeasurement.
ContinuousmonitoringofCO
2concentrationis
doneaspartofsomeGHenvironmentalcontrol
systemsusingCO
2monitor.
Thedifferencebetweentheamountoflight
radiatedbytheIRlampandtheamountofIR
lightreceivedbythedetectorismeasured.Since
thedifferenceistheresultofthelightbeing
absorbedbytheCO
2moleculesintheairinside
thetube,itisdirectlyproportionaltothenumber
ofCO
2moleculesintheairsampletube.

34. Sunshine Recorder
Asunshinerecorderisadevicethatrecordstheamountofsunshineata
givenlocationorregionatanytime.Sunshinerecorderisusedtomeasure
thedurationinhoursofbrightsunshineduringthecourseoftheday.
Itessentiallyconsistsofaglassspheremountedinasectionofspherical
brassbowlwithgroovesforholdingtherecordercards.
Thehoursofbrightsunshinearerecordedbytheraysofthesunpassing
throughthesphere,whichundergofocusandburnaholethroughthecard
placedbehindit.Thecarditselfiscalibratedsothatthehoursandminutesof
thedayaremeasuredacrossit.
Therearesetofgroovesfortaking
threesetsofcards,longcurvedfor
summer,shortcurvedforwinterand
straightcardsatequinoxes.
Thesphereburnsatraceonthecard
whenexposedtothesun,thelengthof
tracebeingadirectmeasureofduration
ofbrightsunshine.

35. Pyranometer
Apyranometerisaninstrumentforthemeasurementofthesolarradiation
receivedfromthewholehemisphere.Itmeasureglobalirradiance,the
amountofsolarenergyperunitareaperunittimeincidentonasurfaceof
specificorientationemanatingfromahemisphericalfieldofview.The
globalirradianceincludesdirectsunlightanddiffusesunlight.
Theworkingprincipleoftheitmainlydependsonthedifferencein
temperaturemeasurementbetweentwosurfaceslikedarkandclear.The
solarradiationcanbeabsorbedbytheblacksurfaceonthethermopile
whereastheclearsurfacereproducesit,solessheatcanbeabsorbed.The
thermopileplaysakeyroleinmeasuringthedifferenceintemperature.The
potentialdifferenceformedwithinthethermopileisduetothegradientof
temperaturebetweenthetwosurfaces.Theseareusedtomeasurethesumof
solarradiation.
Thesolarradiationspectrumthat
reachesearth'ssurfaceextendsits
wavelengthapproximatelyfrom
300nmto2800nm,97%ofthesun’s
spectraldistribution“totalsolar”
radiation.UnitsareWm
-2
.

36. Net Radiometer
Anetradiometerisatypeofactinometerusedtomeasurenetradiation(NR)
attheEarth'ssurfaceformeteorologicalapplications.Thenamenet
radiometerreflectsthefactthatitmeasuresthedifferencebetween
downward/incomingandupward/outgoingradiationfromEarth.
Itisbasedonathermopilesensorwhosewarmjointsareinthermalcontact
withthereceiverwhiletheuppercooljointsareinthermalcontactwiththe
lowerreceiver.Thetemperaturedifferencebetweenthetworeceiversis
proportionaltothenetirradiation.
Thetemperaturedifferencebetween
hotandcoldjunctionisconverted
intoavoltagebySeebeckeffect.The
tworeceiversaremadefroma
portionofsphericalcoatedTeflon.
Theparticularformofthetwo
receiversprovidesaresponsein
accordancewiththecosine.

37. Spectroradiometer
Itsplitsincomingradiationintoindividualwavelengthsorprescribed
wavebands,thenmeasurestheirradiance(energy)ofthephotons.It
measuresspectralirradianceasµMolm
-2
s
-1
nm
-1
orWm
-2
nm
-1
.
Spectrometersdiscriminatethewavelengthbasedonthepositionthelighthits
atthedetectorarrayallowingthefullspectrumtobeobtainedwithasingle
acquisition.
Mostspectrometershaveabasemeasurementofcountswhichistheun-
calibratedreadingandisthusimpactedbythesensitivityofthedetectorto
eachwavelength.Byapplyingacalibration,thespectrometeristhenableto
providemeasurementsofspectralirradiance,spectralradianceand/orspectral
flux.
Thisdataisalsothenusedwithbuiltinor
PCsoftwareandnumerousalgorithmsto
providereadingsorIrradiance(W/cm
2
),
Illuminance(lux),Radiance(W/sr),
Luminance(cd),Flux(LumensorWatts),
Chromaticity,ColorTemperature,Peak
andDominantWavelength.

38. LAI meter
Leafareaindex(LAI)isameasureforthetotalareaofleavesperunit
groundareaanddirectlyrelatedtotheamountoflightthatcanbe
interceptedbyplants.Itisanimportantvariableusedtopredict
photosyntheticprimaryproduction,evapotranspirationandasareference
toolforcropgrowth.
Leafareaindex(LAI)quantifiesthe
amountofleafmaterialinacanopy.By
definition,itistheratioofone-sidedleaf
areaperunitgroundarea.
Itisalightweight,portable,lineararrayof
photosyntheticallyactiveradiation(PAR)
sensorsfornon-destructivemeasurements
ofleafareaindex.Itallowsyoutomeasure
canopyPARinterceptionandcalculate
LAIatanylocationwithinaplantorforest
canopy.

39. Soil thermometer
Mercury-in-glassthermometerareusedforthispurpose.Thebulbisinserted
intoaholeinthegroundwiththestemlyingalongthesurface.A
thermometerthathasbeenfusedintoanouterprotectingglassshieldisused
formeasurementatgreaterdepths.Toobtainameasurement,theinstrument
isloweredintoasteeltubethathasbeendrivenintothesoiltothedesired
depth.
Digitalsoilthermometersarealsousedformeasurementofsoiltemperature.
Asoiltemperaturethermometercanperforma
measurementinfivesteps:
1.Determinetheproperdepthtoperformthe
measurement.
2.Useascrewdrivertomakeapilothole.This
ensuresthatthethermometer’sprobewillnotbe
damagedifforcedintohardsoil.
3.Insertthethermometerintothepilothole.
4.Provideshadeifthesunisbright.Thisensuresthat
thereadingisaccurate.
5.Takeareadinginthemorningandlateafternoon,
andthenaverageouttheresults.

40. Pollinator
Pollinationisaprocesswherethepollenfromthemalepartsoftheflowerare
transferredtofemaleflowerorfemalepartsoftheflower.Thisprocesshasto
happenforthefruitsetting.
Innature,thishappensinmultipleways.Beesdomostofthepollinationand
pollinationbywindalsohappens.ButwhenyouaregrowingplantsinaGHor
aclosedenvironmentwherebeescan’tenterandthereisnotalotofwind,the
growerneedstohelpinthepollinationprocess.
ToassistpollinationinyourGH,youneedapollinatorthatcanbeusedto
pollinateflowersthathavetheirmaleandfemalepartsinthesameflower.
Thisflowerpollinatorisasimpletoolthatcausesvibrationoftheflower
stalkresultinginpollination.

41. Tensiometer
Atensiometerisadeviceformeasuringsoilwater
tension.Itconsistsofacylindricalpipeaboutone
inchindiameterwithaporousceramiccupattached
tooneendandavacuumgaugeattachedtotheother.
Itindirectlymeasuresoilmoisturetension.
Tensiometerreadingsareeasilyinterpretedand
indicatethesoilwaterconditionsexperiencedbythe
plants’roots.
Tomeasuresoilwatertension,theendofthe
tensiometerwiththeporouscupisinsertedthrougha
pilotholeinthesoil,whichhasbeenmadewithasoil
probe.
Afterinstallationthetensiometerisfilled
withwaterandallowedtoequilibratewith
thesoilwaterforabouttwenty-fourhours.
Tensiometersshouldbeinstalledinthezone
ofgreatestrootdensity,ataboutone-quarter
toone-thirdofthemaximumrootdepth.
Tensiometerindicatewhentoirrigate,butnot
howmuchtoirrigate.

42. Daily light integral (DLI) meter
Dailylightintegral(DLI)describesthenumberof
photosyntheticallyactivephotons(individualparticles
oflightinthe400-700nmrange)thataredeliveredtoa
specificareaovera24-hourperiod.
Thisvariableisparticularlyusefultodescribethelight
environmentofplants.
DLIisusuallycalculatedbymeasuring
thephotosyntheticphotonfluxdensity(PPFD)in
μmol·m
−2
·s
−1
(numberofphotonsinthePARrange
receivedinasquaremeterpersecond)asitchanges
throughouttheday,andthenusingthattocalculatetotal
estimatednumberofphotonsinthePARrangereceived
overa24-hourperiodforaspecificarea.
Inotherwords,DLIdescribesthesumofthepersecond
PPFDmeasurementsduringa24-hourperiod.

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