Agriculture/Horticulture

LED Light

For Plant

Photosynthetically Active Radiation

(PAR)

Identified visible wavelength• 660nm – drives the engine of the

photosynthesis

• 612nm – Not to promote

photosynthesis, but to match

carotenoids (plant health). Increase

plant’s chlorophyll contents

• 465nm – Proper photomorphogenesis

or plant development

• Sunlight contains 4% ultraviolet

radiation, 52% infrared radiation and

44% visible light

Why do plant have photoreceptors?

There are three principle families of such photoreceptors

1)Red/Far-Red (R/FR) light-absorbing phytochromes

2)UV-A/blue light-absorbing cryptochromes

3)Phototropins

R:FR Photon ratio

Relationship between R:FR and Pfr/P

Effect of R:FR Ratio (Zeta,ξξξξ) On Plant

High R:FR

(Leafy)

Low R:FR

(Thin & Long)

Flowering

• The flowering process is particularly intriguing because, in most plants, it is precisely synchronized with seasonal changes. Certain plant species do not flower if the days are too long; others flower only when daylight lasts longer than a certain number of hours. This observation suggests that plants can assess the changing length of the day as the seasons come and go, a complex and difficult task. To do so, they must discriminate day from night, measure the passage of time, and integrate the information. Do plants possess the means of carrying out such a complex process? They certainly do. Just as plants measure light with photoreceptors, they measure time, appropriately, with a biological clock. And as for the integration of light and time, we have been able to show, after countless hours of experimentation, that plants are constantly, monotonously making and then destroying molecules that help control flowering. The concentration of those molecules is the key to a seemingly complex decision.

Flowering (Continue)

Totally infrared range. All energy absorbed at this point is converted to

heat.1000+ nm

There is little absorption by chlorophyll here. Flowering and germination is

influenced. At the high end of the band is infrared, which is heat.720 - 1000 nm

This is the red band. Large amount of absorption by chlorophyll occurs,

and most significant influence on photosynthesis. (promotes flowering and

budding)

610 - 720 nm

This range includes the green, yellow, and orange bands and has less

absorption by pigments.520 - 610 nm

This range includes violet, blue, and green bands. Peak absorption by

chlorophyll occurs, and a strong influence on photosynthesis. (promotes

vegetative growth)

400 - 520 nm

Start of visible light spectrum. Process of chlorophyll absorption begins.

UV protected plastics ideally block out any light below this range.380 - 400 nm

Range of UVA ultraviolet light which is neither harmful nor beneficial to

plant growth.315 - 380 nm

Includes harmful UVB ultraviolet light which causes plants colors to fade.280 - 315 nm

UVC ultraviolet range which is extremely harmful to plants because it is

highly toxic.200 - 280 nm

Flowering (Continue)

• The transition to flowering in plants is regulated by environmental factors such as temperature and light. Plants grown under dense canopies or at high density perceive a decrease in the ratio of red to far-red incoming light. This change in light quality serves as a warning of competition, triggering a series of responses known collectively as the 'shade-avoidance syndrome'. During shade avoidance, stems elongate at the expense of leaf expansion, and flowering is accelerated. Of the five phytochromes—a family of red/far-red light photoreceptors—in Arabidopsis, phytochrome B (phyB) has the most significant role in shade-avoidance responses, but the mechanisms by which phyB regulates flowering in response to altered ratios of red to far-red light are largely unknown. Here we identify PFT1 (PHYTOCHROME AND FLOWERING TIME 1), a nuclear protein that acts in a phyB pathway and induces flowering in response to suboptimal light conditions. PFT1 functions downstream of phyB to regulate the expression of FLOWERING LOCUS T (FT), providing evidence for the existence of a light-quality pathway that regulates flowering time in plants.

Shade Avoidance Syndrome

• Shade avoidance is a set of responses that plants display when they are subjected to the shade of another plant. It often includes elongation, altered flowering time, increased apical dominance and altered partitioning of resources. This set of responses is collectively called the shade-avoidance syndrome (SAS).

• Plants can tell the difference between the shade of an inanimate object (eg a rock) and the shade of another plant. In the shade of a plant, is present in a higher irradiance than red light, as a result of the absorption of the red light by the pigments involved in photosynthesis. Phytochrome can be used to measure the ratio of far-red to red light, and thus to detect whether the plant is in the shade of another plant, so it can alter its growth strategy accordingly (photomorphogenesis). In Arabidopsis, phytochrome B is the predominant photoreceptor that regulates SAS.

Shade Avoidance Syndrome (Low R:FR)

Photoperiod

光光光光• 光 感• 感 光 官為 ， 莖 莖 。 剛

， 為 感。 ，極 光 感 果較。 ， 感 2 公 ，。牽 為光 感 。

• 據研究， 光 感 光 (phytochrome)，結 。光 光， 開 ， 開 。間 可見 光， 開 開 。

光 感 開 激• 1936 家Chailakyan 為 經過 ，產 激

， 激 莖 間，份 。 激 為開 激 (Florigen) 。 開 激可 ，故 開 ； 開 激 可產 ，故 光 可開 。

• 經 為光 (Phytochrome) 感 光。光 激 光 ， 產 ，經韌 ，

。• 光 可 ， 光 (Pr) 660nm 光 Pfr ， Pfr 730

nm 光 Pr 光 。

光Pr -------------------> Pfr

Pfr -------------------> Pr

光(dark)

• Phytochrome 、 官 ， 括 間 、、 加 光 ， 個光 。

光 光 去 ， 為Pfr 光

Photoperiod

、、、、• 光 (photoperiod)可控 開 ， 光 間

可 為 :

1. : 求經 、開 , 界 開 .

區晚 開 ， 括 、 蓿甘 。

2. : 較 季 開括 、菊 。

3. : 開 ， 、 、 茄。

4. ： 開 。 甘(Saccharm spontaneum) 為12.5 開 ， 過 均 開 。

• ， 區 ，界 為界 ， 過 開

； 開 。， 剛 感光 開 界 。

Long Day Plant

• , , 開 結果,管 功課, 顧 ,

, 刻幹, 感

開 , 開 ,控 , 光 改

間 感 , 開 ,, , 感

開 開 , 開 , 季過 ,開 光, 感

季 ,經過45 60 開,, 開 ； 間 光

, 較 光 , 感覺 經 ,開 , , 控間 開 , 季 產出來的 .

The Right Duration

• No matter what types of plants you are growing indoors, you must be sure to always give them a rest. When it's dark, plants respirate, which is an important part of their growth process. The balance of rest time to active growth time affects many biological processes, including the growth rate, and the setting of buds and fruit.

• Botanists usually divide plants into three categories relating to their preferred day length: short-day, long-day or day-neutral. Short-day plants, such as chrysanthemums, kalanchoe, azaleas and begonias, will thrive on less than 12 hours of light per day. In fact, these plants must usually go through a series of even shorter days before they will set buds and flower.

• Long-day plants require at least 14 to 18 hours of light each day. Most vegetables and garden flowers are long-day plants, and when they don't receive enough light they get pale and leggy. Day-neutral plants, including foliage plants, geraniums, coleus and African violets, are usually satisfied with 8 to 12 hours of light all year-round.