Light in horticulture

Nghiên cứu ảnh hưởng của ánh sáng đến sinh trưởng cây trồng

Light in horticulture

Light spectrum

Perception of light

– Is hardly used in horticultural entreprises

• Short wave irradiation

– 300 – 3000 nm

– Pyranometer (Kipp & Zonen); solarimeter

• W/m²: instant short wave irradiation per second

• MJ/m² or J/cm²: sum over a determined period of time t

• Used on nursery scale for operating irrigation, screening and

supplementary lighting

• Sensitivity of the human eye

– 555 nm

– Lux-meter

– Also used on nursery scale to control lighting and screening

Conversion factors for different light sources

3.91 2.80 2.61 4.00

18 14 12 20

Sun light High pressure Na-lamp

Conversion to Light source

Unit

(lux)

Seasonal fluctuations in day length and light

Light absorption by the leaf

Light distribution above and beneath the leaves

Photoreceptors

• Light quantity: counting the number of photons

• Light quality: ratio of photons

• Direction of the light: photongradients

• Duration of light: timing of light-dark transitions

• Polarisation: dichromatic photoreceptor-regulation

Structure of chlorophyll

Absorption spectra of chlorophyll and

carotenoids

Structure of phytochrome

Absorption spectra of phytochrome

Hyperbolic relation between φ and the R:FR ratio

Pfr: the active form of phytochrome

• Very low fluence response

• Low fluence response

• High irradiance response

Blue light absorbing pigment (BAP)

Cabbaging of the leaves Non-directional

Phototropism, phototaxis, intracellular rearrangement of chloroplasts

Interactions among photoreceptors

Type I: X and Y have an independent control

Interactions among photoreceptors

Y X

Precursor

X

(phytotrons, tissue culture)

– High pressure sodium

lamps (SON-T): general use

in culture

– Metalhalide lamps: limited

application in Canada

Influence of supplementary lighting on

photosynthesis of cut roses

aantal bloempjes/

bloeiwijze fotoperiodische

Avoidance of flower bud blasting in

Alstroemeria and Eustoma (photo)

Forcing of florist azalea

With supplementary lighting Without supplementary lighting

Forcing of florist azalea

With supplementary lighting Without supplementary lighting

– Deregulates the opening/closing of the stoma

– Stomata remain open for 24 h

– Negative effect on the water balance of the cut flower

Supplementary lighting: lamps and fittings

Different types of lamp holders

Different types of lamp holders

Photoperiodic lighting

Photoperiodic lighting

• Avoidance of flowering in short-day-plants

• Induction of flowering in long-day-plants

⇒ requires knowledge of the “critical day-length”

• Low intensities are sufficient for the expected

response (1-2 µmolm².s)

• Two lamp types:

– Lenghtening the day: SLR-18 Watt lamps

– Cyclic lighting: incandescent lamps

Control of photoperiod via cyclic lighting

incandescent lighting: high ratio of red irradiation

the night is sub-divided in cycles of light en darkness, e.g a cycle of 30

min whereby lamps are switched on for 10 min

Control of the photoperiod by use of day extension:

SLR or compact gas discharge lamps - lifetime lamp: 6000h

the natural night is extended to reach the critical daylength

Source-sink effect of photoperiod in Gladiolus

Effect of photoperiod on dry matter production

in different organs of Gladiolus

725-735 nm)

R/FR (600-700 nm/

700-800 nm)

„

Spectral filters

Spectral distribution of 3 CuSO4-filters

Influence of spectral filters on the morphology

Internode lenght (cm)

CuSO4 conc (%)

0 2 4 6 8 10 12 14 16

0,8 0,9 1,0 1,1 1,2 1,3 1,4 1,5 1,6

Transmission by interferention filters

Effect of spectral filters

Light spectra for 2 filters in comparison with standard

plastic covering, measured on a cloudy day

Shoot growth in cut chrysanthemum as related to

spectral light quality

Dendranthema 'Charm Dark'

Growing period (days)