Indoor Crop Production Exam 1

Exam 1

What are quantum units? Why do we use them in CEA?

What is PAR?

photosynthetically active radiation (PAR)

400-700 nm

Similar to visible light spectrum (380-770nm)

Infra-red (700-1,100 nm) photons traditionally believed to not have enough energy to support photosynthesis (increase temperature)

What is PPFD?

Photosynthetic photon flux density

PPFD; µmol·m–2·s–1

How do plants absorb these photons?

• Light energy captured by chlorophylls and accessory

pigments is converted into:

NADPH – reducing power

ATP – chemical energy

• Two photosystem complexes that occur in series in the thylakoid membrane

  PSI

  PSII

Quantum yield

Moles of CO2 fixed per mole of quanta (photons) absorbed (efficiency of light for driving photosynthesis

→ Generally highest under red wavelengths

Lower quantum yield of blue and green due to:

-Absorption by non-photosynthetic pigments (flavonoids)

¤Heat dissipation by carotenoid

PHOTOSYNTHESIS: Four Major Protein Complexes

1. PSII: oxidizes water (2H2O → 4H+ + 4e- + O2)

- Releases protons in thylakoid lumen

- Reduced product is PQH2 - PQ + 2e- → PQ2-

- PQ2- + 2H+ → PQH2

2. Cytochrome b6f: oxidizes PQH2

- Delivers electrons to PSI via PC- Oxidation coupled to proton transfer into lumen

3. PSI: reduces NADP+ to NADPH in stroma

***(NADPH = first product)

- PC reduces P700

- NADPH via Fd and FNR

4. ATP synthase: photophosphorylation

Product from 1. PsII:

O2

4 electrons

4 protons
(protons released into lumen)

How many ATP can be produced from 4 protons? (PSI)

1ATP per 4 protons (H+)

***product #2 from PSI= 3ATP****

molecules of products produced from photosynthesis?

2 NADPH

&

3 ATP

How many moleculess of ATP/NADPH are needed to fix 1 molecule of CO2?

3 ATP

2 NADPH

How many Photons can fix 1 molecule of CO2

8 Photons!

How many molecules of CO2 can be fixed for each photon of light?

0.125 molecules of CO2

Fates of Light:

• Reflected

• Transmitted

• Absorbed

-Photosynthesis

-Heat

-Chlorophyll fluorescence

With the Fate of absorbed light:

Photosynthesis, Dissipated as heat ,Chlorophyll fluorescence are these in competition? Y/N?

YES

These three occur in competition…

→Increase in efficiency of one decreases the yield of the other two →If we can measure yield of chlorophyll fluorescence, this can give us information about changes to photochemistry and heat dissipation

chlorophyll fluorescence

Remitted energy from oversaturated photosystem II

Once PSII absorbs light and plastoquinone accepts an electron, it cannot accept another electron until it has passed the first onto the subsequent electron carrier

→During this period, the reaction center (PSII) is said to be “closed” →Closed reaction centers leads to an overall reduction in the efficiency of photochemistry…resulting in increased chlorophyll fluorescence

Three dimensions of light we are concerned with:
(All three are important in plant growth and development)

1. Quantity (intensity)

2. Quality (color)

3. Duration (photoperiod)

Daily light integral (DLI):

Cumulative amount of light received by the plant each day as a function of light intensity and duration

¤Similar to a rain gauge

¤mol·m–2·d–1

Would you get the same measured DLI from outside if you measured DLI inside a greenhouse? Y/N?

NO

Average DLI inside a greenhouse < %30 mol·m-2·d-1

Factors affecting DLI in a greenhouse

¤Greenhouse orientation

¤Time of the year

¤Day length (photoperiod)

¤Greenhouse glazing and coverings

¤Greenhouse structure and equipment

¤Hanging baskets

Plant responses to increased DLI: (general increase in light)

¤Leaves (smaller and thicker)

¤Flowers (more and larger)

¤Time to flower (faster, due partly to temperature)

¤Branching (increased)

¤Stem diameter (increased)

¤Root growth of plugs and cuttings (increased)

What is a normal orientation of a gutter connected greenhouse?

N/S

(E/W maximizes light but casts shadows)

Benefits of a higher DLI:

• Higher quality

  Compaction

  Increased biomass

  Increased branching

• Flowering

  Earlier

  Increased

• Greater yield

Quantum sensor measures _______?

Quantum sensor measures PPFD.

You are a plug producer targeting a greenhouse DLI of 12 mol·m–2·d–1 in January.

The average solar DLI in the greenhouse during this time of the year is 7 mol·m–2·d–1.

You currently have HPS lamps providing 60 µmol·m–2·s–1 at canopy height with a 16-h photoperiod.

Can you achieve your target DLI with the current supplemental lighting setup?

NO, only 10.456mol*m^-2*s^-1

(only 3.456 mol*m^-2*s^-1 from HPS lamps, + 7 mol*m^-2*s^-1 from DLI)

How can a grower easily increase DLI without changing fixtures of supplemental lighting?

increase operating hours

You are a plug producer targeting a greenhouse DLI of 12

mol·m–2·d–1 in January.

The average solar DLI in the greenhouse during this time of the year is 7 mol·m–2·d–1. With a 20-h photoperiod.

What is the minimum PPFD required from supplemental lighting to achieve this target DLI?

Lighting Basics – Daily Light Integral (DLI): general DLI requirements

“Good” plant growth in greenhouses generally requires 10 to 12 mol·m-2·d-1

(THIS VARIES DEPENDING ON CROP)

Supplemental Lighting:

µmol·m^-2·s^-1 ranges for Floricuture & Vegetable Crops

¤50-75 µmol·m–2·s–1 (floriculture crops)

¤100-200 µmol·m–2·s–1 (vegetable crops)

Benefit of supplemental lighting greatest:

¤From October through March (North)

¤From November through February (South)

¤During non-sunny conditions (during the night and on cloudy days)

Supplemental Lighting Guidelines for Fruiting Vegetables

SI units for DLI measurements

mol·m-2·d-1

Chlorophylls a and b

• Light absorption for photosynthesis located in chloroplast

Chl a absorbs light maximally at 430 and 663 nm

Chl b absorbs light maximally at 453 and 642 nm

Does green light drive photosynthesis?

• Lower absorbance allows green light to penetrate deeper

into the leaf

Upper mesophyll cells are often light saturated

Green light reaches chloroplasts in lower cells that (not yet light saturated)

• Proposed that green light may enhance overall leaf photosynthetic rate

Basic LED Terms: Forward current (A)

Forward current (A): the maximum forward current allowed for continuous operation

Basic LED Terms: Radiant flux

Radiant flux: the amount of radiant energy (J) emitted per unit of time (s)

Basic LED Terms: Peak wavelength (nm)

Peak wavelength (nm): The wavelength at which the spectral radiant flux [W·nm-1] in the spectral radiant flux distribution curve (spectrum) of an LED is the maximum

Basic LED Terms: Half-width (nm)

Half-width (nm): The width of the spectral radiant flux distribution curve (spectrum) at 50% of the maximum spectral radiant flux. It is a measure of the light monochromaticity

Basic LED Terms: Efficiency

ratios with the same units in the numerator and denominator

¤Example: Lamp efficiency (W·W–1)

¤Example: Quantum efficiency (mol·mol–1)

Basic LED Terms: Efficacy

ratios with different units in the numerator and denominator

¤Example: Lamp efficacy (μmol·J–1)

¤Example: Photon efficacy (μmol·J–1)

What color light has the lowest photon efficacy?

Green! ~1.3-1.9

White LEDs consist of blue LEDs with ____?

White LEDs consist of blue LEDs with a luminescent material coating

Commonly a phosphor material (Y3Al5O12Ce)

¤Absorbs blue photons and luminesces at longer wavelengths

Efficacy of production: Edry = Fa × QY × CUE × HI × k

Edry: grams of dry mass produced per mol of photons

Fa: fraction of photons absorbed

QY: quantum yield (mol carbon fixed per mol photons absorbed)

CUE: carbon use efficiency (mol carbon in plant biomass per mol carbon fixed)

HI: harvest index (mol edible carbon per mol carbon in total biomass)

k = 30 (constant that represents mass of CH2O in grams per mol of carbon in edible product)

Efficacy of production: Edry = Fa × QY × CUE × HI × k
what is Fa?

Fa: fraction of photons absorbed

Efficacy of production: Edry = Fa × QY × CUE × HI × k
What is QY?

QY: quantum yield (mol carbon fixed per mol photons absorbed)

Efficacy of production: Edry = Fa × QY × CUE × HI × k
What is CUE?

CUE: carbon use efficiency (mol carbon in plant biomass per mol carbon fixed)

Efficacy of production: Edry = Fa × QY × CUE × HI × k
What is HI?

HI: harvest index (mol edible carbon per mol carbon in total biomass)

Efficacy of production: Edry = Fa × QY × CUE × HI × k
What is k?

k = 30 (constant that represents mass of CH2O in grams per mol of carbon in edible product)

Efficacy of production: Edry = Fa × QY × CUE × HI × k
What is Edry?

Edry: grams of dry mass produced per mol of photons

spectrum of light types/sources:

White LED (Blue with phosphor)

Fluorescent Lamp

High pressure mercury lamp

High pressure Sodium lamp

metal halide

Monochromatic Led

The higher the (K) kelvin color scale (cool white/blue), the ____ the photon efficacy.

The higher the (K) kelvin color scale (cool white/blue), the higher the photon efficacy.

(More the phosphorus coating on LED dissipates photons as heat (makes it more red/less blue) the less energy)

Supplemental Lighting:

Watts (J/s)

PAR output (umol/s

Efficacy (umol/J)

Cost per fixture ($)

**all of these figure have gone up as of 2025**

Canopy Photon Capture Efficiency: How can it be reduced?

Light Mapping

When is it most beneficial to provide supplemental lighting to a crop?

Under what circumstances is supplemental lighting necessary?

When the DLI is not sufficient (short days, cloudy days, manipulate photoperiod.

Most benefit gained within linear portion of Light Saturation curve

(LSP Light Saturation Point)

As light intensity increases, the benefit to photosynthesis ______until saturation occurs.

As light intensity increases, the benefit to photosynthesis decreases until saturation occurs

Greenhouse tomato example:

¤ Turn off supplemental lighting when ambient light intensity is >600 µmol·m–2·s–1

¤ Cloudy days, morning, and nights are often most beneficial ¨ Most benefit gained within linear portion of curve

High-wire Vegetable Production: In terms of lighting, what is a potential problem that might affect productivity?

Crop growth uniformity and productivity are influenced by the homogeneity and intensity of light delivered to the entire foliar canopy

¨ Interior leaves often receive very low light intensities

¤ Deteriorating photosynthetic capacity

¤ Contribute to net respiratory carbon losses and premature senescenc

LAI Leaf Area Index

LAI: ‘one-sided’ leaf area per unit area of ground

(LAI = leaf area / ground area, m2 / m2)

higher LAI = larger canopy → higher Light Saturation Point (LSP)

How do we increase productivity in the lower canopy for high-wire crops?

Crop growth uniformity and productivity are influenced by the homogeneity and intensity of light delivered to the entire foliar canopy ¨ Interior leaves often receive very low light intensities

¤ Deteriorating photosynthetic capacity

¤ Contribute to net respiratory carbon losses and premature senescence

Pn or A

Pn→ net photosynthetic rate
A→Assimilation

Light compensation point

light intensity at which net photosynthesis (Pn) is 0

Light saturation point

light intensity at which further increases in light intensity do not increase photosynthesis

¤ Leafy vegetables generally <1,000 µmol·m–2·s–1

¤ Tomato and cucumber >1,000 µmol·m–2·s–1

Quantum yield

the maximum efficiency at which plants can use incident radiation to fix CO2

¤ Theoretical maximum for C3 plants is 0.125 mol·mol –1

¤ 1 mol of CO2 fixed per 8 mol of absorbed photons

Supplemental Lighting Controls: Timer control

Issues with this method?

Set photoperiod and timer will automatically turn lights on or off

not efficient! the PPFD will change throughout the day → may have light on when PPFD exceeds desired amount

Supplemental Lighting Controls: Threshold control

Set a threshold for when lighting turns on/off during photoperiod

-Multiple quantum sensors measure light in greenhouse

-When ambient PPFD exceeds or falls below a defined threshold, the lights turn off or on, respectively

HPS lamps will lose life if turning on and off like this

(more efficient than timers, turns on and off when needed)

Supplemental Lighting Controls: Dimming control

Same as threshold control, but we can now dim the fixtures to more precisely maintain our target PPFD

(with established threshold, will adjust voltage for output light, think duty cycle and LED power,less photons supplied when more PPFD available)

Supplemental Lighting Controls: Predictive lighting controls

¤ Utilize 7-day weather forecasting as well as historical weather averages

-Makes predictive control decisions to reduce energy costs and avoid plant stress

¤ Concept of “carry-over DLI”

-We can lower the target for the DLI following a sunny day with more than the required DLI

-Can also use less supplemental lighting during cloudy weather if following day is anticipated to be clear and sunny

Supplemental Lighting Controls: Adaptive lighting control

¤ PPFD of supplemental light is continually adjusted so that sunlight combined with supplemental light reaches, but does not exceed, a target DLI at the end of a specified photoperiod

Intra-canopy lighting strategies: