I'm " leaning more" to the " low energy " side ,of artificial lighting for plants...
Meaning ,growing with LEDS...( only ) .
In nature, photon irradiance (photon flux density) can fluctuate over three orders of magnitude and these changes can be rapid. However, plants have evolved with photosynthetic systems that operate most efficiently at low light. Such efficiency confers an obvious selective advantage under light limitation, but predisposes to photodamage under strong light. How then can leaves cope? First, some tolerance is achieved by distributing light over a large population of chloroplasts held in architectural arrays within mesophyll tissues. Second, each chloroplast can operate as a seemingly independent entity with respect to photochemistry and biochemistry and can vary allocation of resources between photon capture and capacity for CO2 assimilation in response to light climate. Such features confer great flexibility across a wide range of light environments where plants occur ....
....Distributing light absorption between many chloroplasts thus equalises effort over a huge population of these organelles, but also reduces diffusion limitations by allowing placement of chloroplasts at optimal locations within each cell.
...A regular, parallel arrangement of palisade cells with chloroplasts all vertically aligned means that about 80% of light entering a leaf initially bypasses the chloroplasts, and measurements of absorption in a light integrating sphere confirm this.
....Chloroplasts near the upper surface have ‘sun’-type characteristics which include a higher ratio of Rubisco to chlorophyll and higher rate of electron transport per unit chlorophyll. Chloroplasts near the lower surface* show the converse features of ‘shade’ chloroplasts. Similar differences between ‘sun’ and ‘shade’ leaves are also apparent. Chloroplast properties do not change as much as the rate of absorption of light. Consequently, the amount of CO2 fixed per quanta absorbed increases with increasing depth beneath the upper leaf surface. *The lower half of a leaf absorbs about 25% of incoming light, but is responsible for about 31% of a leaf’s total CO2 assimilation.
Shade leaves ,assimilate more CO2,than sun adapted leaves ...
Chl a and Chl b differ with respect to both role and relative abundance in higher plants. Chl a/b ratios commonly range from 3.3 to 4.2 in well-nourished sun-adapted species, but can be as low as 2.2 or thereabouts in shade-adapted species grown at low light. Such variation is easily reconciled with contrasting functional roles for both Chl a and Chl b. Both forms of chlorophyll are involved in light harvesting, whereas special forms of only Chl a are linked into energy-processing centres of photosystems. In strong light, photons are abundant, consistent with a substantial capacity for energy processing by leaves (hence the higher Chl a/b ratio). In weak light, optimisation of leaf function calls for greater investment of leaf resources in light harvesting rather than energy processing. As a result the relative abundance of Chl b will increase and the Chl a/b ratio will be lower compared with that in strong light. As a further subtlety, the two photosystems of higher plant chloroplasts (discussed later) also differ in their Chl a/b ratio, and this provided Boardman and Anderson (1964) with the first clue that they had achieved a historic first in the physical separation of those two entities.
Leaves absorb visible light very effectively (>90% for all wavelengths combined; solid curve).Wavelengths corresponding to green light are absorbed less effectively (absorptance drops to c. 0.75). Beyond 700 nm (infrared band) absorptance drops to near zero, and forestalls leaf heating from this source of energy. Quantum yield is referenced to values obtained in red light (600-625 nm), which ismost effective in driving photosynthesis, requiring about 10 quanta per CO2 assimilated (based on high-precision leaf gas exchange) compared with about 12 quanta at the blue peak (450 nm). Quantum yield shows a bimodal response to wavelength. Absorptance drops beyond 700 nm but quantum yield drops off even faster because PSII (responsible for O2 generation) absorbs around 680 nm and cannot use quanta at longer wavelengths in this measuring system. UV wavelengths (below 400 nm) are capable of driving photosynthesis, but as a protective adaptation vascular plants accumulate a chemical ‘sunscreen’ in response to UV exposure. Field-grown plants are especially rich in these substances so that absorbed UV is dissipated harmlessly, lowering quantum yield compared with growth-chamber plants. (Based on McCree 1972)
The Quantum yield (quantum efficiency) is variously and rather confusingly defined for photosynthesis
• “The number of photochemical products” (such as moles of CO2 assimilated or O2 evolved]) divided by
the “Total number of quanta absorbed”. ( umoles CO2 assimilated or umoles O2 evolved / umoles of light )
(widely accepted as most precise )
• “The fraction of excited molecules” (i.e., excited by the absorption of a photon) that decay via a
designated pathway (such as via photochemistry, apparently no matter how small the effect produced
per quantum), or
• The number of times that a defined event occurs per photon absorbed by the system
Effect On Quantum Yields By O2, CO2, Temperature, And Light Levels
Under current atmospheric conditions with 380 ppm CO2, the quantum yield of C3 and C4 leaves are
similar at about 0.04 to 0.06 mole of CO2 assimilated per mole of photons absorbed. The reduction from
the theoretical quantum yield of c. 0.125 is due to losses from photorespiration (in C3 plants) or to energy
loss from CO2 concentrating mechanisms (in C4 plants).
Effect of O2, Temp, and CO2 may be summarized:
• Oxygen: C3 plants in low O2 environments have lower photorespiration and higher photosynthetic
quantum yield, whereas C4 plant do not improve in lower O2.
• Temperature: C3 plants in lower temperature environments have higher quantum yield than C4 plants,
whereas at higher temperatures, C4 plants have higher quantum yield, although these differences are
modest over moderate temperature ranges.The quantum yield of C4 plants in almost constant
over temperature range of 10 - 40 ºC
• CO2: C4 plants in lower CO2/O2 ratio environments have more efficient PS, whereas the opposite is true
in higher CO2/O2 ratio environments.
Sun and shade plants “show very similar quantum yields”[for quantum yields expressed in terms of
mol CO2 fixation per absorbed quantum]. However, the maximal PS CO2 assimilation of sun plants at
saturation (example: c. 35 μmol CO2 m-2 s-1) is substantially higher than for shade plants (example: c. 5
μmol CO2 m-2 s-1,). ( this is apparently not contradictory, since quantum yield at least
by some definitions does not quantitate how much effect each of the absorbed photons utilized has, see
earlier discussion of definitions of quantum yield.) This indicates that earlier growing conditions affect how
much capacity for PS the leaf develops. Above saturation, the leaf is said to be “CO2 limited”—the Calvin
cycle processes cannot keep up with the absorbed light energy producing ATP and NADPH.
Relative quantum Yield [ RQE ] :“The number of photochemical products” (such as moles of CO2 assimilated or O2 evolved]) divided by
the “Total number of quanta absorbed”.Per nanometer .
From 600 to 630 nm for every mole of photons - 6.022 × 1023 - 1 mole of CO2 is assimilated ...
When investigating phytochrome responses, it would at first appear that an investigator should be very concerned about the relative balance between the λ = 660 nm and λ = 730 nm in the light source. Although important in selecting a lamp source, in practice, the most relevant factor in photobiology is the fraction of phytochrome present in the active (Pfr) form with respect to the total phytochrome (Ptot = Pfr + Pr) at photoequilibrium.
Although Pr has λmax = 660 nm and Pfr at λmax = 730 nm, there is significant overlap in the relative spectral absorbance of Pr and Pfr (Fig. 2). As a result of the relative differences in absorption and the subsequent conformational change between Pr and Pfr, both forms are present in the plant. The relative proportion of active form (Pfr) to the total (Ptot) is considered the phytochrome photostationary state (Φ). It is this relative proportion of Pfr to Ptot that regulates a given photomorphogenic response. Because the absorption spectrum of each form is known, it is possible to estimate Φ if the spectral distribution of a light source is also known
Typical values of Φ under ambient solar conditions are Φ = 0.6 for full sun and Φ = 0.1 for dense shade under a full canopy (Salisbury and Ross, 1992; Nagy and Schaefer, 2002), although these values vary according to canopy type and density (Vandenbussche et al., 2005). The range of values from electric light sources vary from Φ = 0.1 from a far red rich light source to Φ = 0.89 from a source with high red spectrum (Sager and McFarlane, 1997).
The values for estimating Φ derived from isolated phytochrome (Sager and McFarlane, 1997; Sager et al., 1988) are useful guides to determining the effect of any light source on the phytochrome response. When using narrow-band LEDs, the Φ can be approximated based on the λmax of the LED. Table 2 shows the estimate of Φ for discrete narrow-band LEDs with λmax from 300 to 800 nm. Table 2 also includes relative quantum efficiency (RQE) for photosynthesis (McCree, 1972) to allow the photosynthetic efficiency of a given wavelength to be evaluated as well. These well-defined parameters allow the spectra to be optimized for both photosynthesis and photomorphogenesis.
Light-emitting diodes to understand the flowering response of a short-day strawberry
Takeda and Newell (2006) have observed that short-day strawberries that are grown in the greenhouse under long-day conditions can be induced to flower in the fall without exposure to cool temperatures or short days. This unexpected result was attributed to very high planting density (200 plant/m2) of the plug plants in the greenhouse. Takeda et al. (2008) stated that broad spectra light was absorbed by the canopy, but only wavelengths greater than 700 nm were being detected by the crown, resulting in an Φ < 0.2 at crown level.It was hypothesized that the early flowering response was phytochrome-mediated. To test this hypothesis, high-density strawberries were established under long days in a greenhouse (Φ = 0.62) and then transferred to a controlled environment chamber with broad spectra fluorescent lamps (Φ = 0.66) under long-day conditions (16-h light/8-h dark). A strand of low-output red LEDs (λmax = 662) was used to illuminate the crown and increase the Φ to 0.75 . This treatment was applied for 28 d and then the plants were transplanted in the field under a high tunnel production system.
After 2 months under high tunnel conditions,83% of the plants without the supplemental red LED treatment were flowering, whereas less than half (47%) of the plants with the LED (red 662 nm ) treatment were producing flowers.These data strongly suggested the maintenance of the vegetative state of the crown under short-day plants is under phytochrome control and suggests that manipulation of the crown light environment using LEDs to promote earlier flowering could be a tool to increase off-season production of strawberry.
Does it suggest anything else,maybe ?
Photosynthesis in sun and shade
Plants have adapted to an extraordinarily wide range of light environments, from the deep shade of rainforest understoreys and underwater habitats to the high-radiation environments of deserts and mountain tops. Exploitation of such a wide diversity of habitats is possible because plants have evolved various mechanisms to optimise their use of sunlight. Many plants also exhibit great plasticity in their response to changes in light availability within a particular habitat. This potential for acclimation enables them to exploit more variable environments than plants with a narrower range of responses to light. This section will cover some features that make a plant suited to either a high or low light environment.
In low light, plants obviously need to absorb sufficient light for photosynthesis if they are to survive. To do this they need to maximise light absorption. In a high light environment however, the problem is reversed, with plants needing to maximise their capacity for utilising abundant light energy, while at the same time dealing with excess sunlight when photosynthetic capacity is exceeded. As a consequence of such unrelenting selection pressures, plants have evolved with a variety of features that optimise light interception, absorption and processing, according to the nature of the light environment to which they have adapted .
Adaptation implies a genetically determined capability to acclimate to either sun or shade. Such acclimation calls for adjustment in one or a number of attributes concerned with interception and utilisation of sunlight. Common features of either sun or shade plants are outlined below, and their advantage to plants growing in different light environments is discussed. Field applications are illustrated via sun/shade acclimation and sunfleck utilisation in rainforest plants.
A higher photosynthetic capacity in sun plants does, however, incur some costs. Their leaves tend to have higher respiration rates which increase light-compensation point relative to shade plants (Figure 12.7). Higher respiration rates probably result from (1) increased carbohydrate processing in high light, (2) increased costs of constructing sun leaves and (3) a higher cost of maintaining sun leaves (further details on maintenance costs are given in Section 6.5).
Greater transpiration is a further cost of higher photosynthetic capacity due to higher stomatal conductance. Sun plants often respond to this by increasing their root : shoot ratios. Under conditions where water is limiting, however, stomatal conductance may be reduced, sacriﬁcing photosynthesis in favour of slower transpiration.
Photoinhibition and photoprotection
Sun/shade acclimation and rainforest gaps
Interaction of light and nutrients on rainforest seedlings
Ultraviolet radiation and plant biology
i.e for Toona plant :
At 30 umol/sec PPF = 17 gr / m^2 lamina mass (leaf blade mass )
At 130 umol/sec ( +433 % more power ) = 36 gr / m^2 ( +212 % more mass )
At 535 umol/sec ( +1783 % more power ,from 30 umol/sec ) =48 gr / m^2 (+282 % more mass ,than at 30 umol/sec)
2 x ( 30 umol/sec per squar. meter ) = 34 gr total ...
Almost same leaf mass yield as 130umol/sec per 1 squar.meter .....
But with less than half power ( 60 umol/sec vs 130 umol/sec ).....
Well...It kinda explains why ,with leds ,utilisation of multiple ,low powered, panels ,
is way more efficient ,than having one panel of great power....
Efficiency is (also) a matter of light power distribution and not a matter of absolute power (only )...
The more ,the research about leds & growing plants advances...
The more I reach to a certain conclusion...
For low/moderate power grow sites ( PPD up to 500 umol /sec/ m^2 ) :
Shade Adapted plants is the best way to go...
Lots of @350mA leds ,placed in small powered multiple panels...
With "basic" led config being :
WW ( 2500-2700 K ) : CW (6500-7500 K ) : RED 630 nm (620-640 nm )
At 3:2:1 output-photon flux -power ratios,respectively
(For non-branded leds )
White average efficiency :0.3
(Mostly for Bridgelux Chips.Pretty good quality chips ,but Yag Phosphor layering/ general manufacturing techniques, do vary a lot .)
Red Average efficiency : 0.3
( Mostly for Epistar chips.Pretty good quality chips )
12 x WW= (approx.) 3.6 Watts flux
8 x CW= (approx.) 2.4 Watts flux
4 x 630 nm = (approx.) 1.2 Watt
3.6 : 2.4 : 1.2= 3:2:1 (approx.)
Total :7.2- (approx)
Average PPF : 30-35 umol/sec
Blue (400 – 499nm) :14%
Green (500 – 599nm) :35% (not so much flux under 560 nm .Most power is at 560-599 nm range. )
Red (600 – 699nm):48%
Far Red (700 – 750nm):3%
CIE X-Coordinate : 0.422
CIE Y-Coordinate : 0.360
CCT :2876 °K
CRI : 94
For High power grow sites ( PPD over 500 umol /sec/ m^2 ) :
Sun Adapted plants is the best way to go ,at this case...
Powerful leds ,maybe lensed to 90°-60° and actinics...
Best configs should contain both 660 & 630 reds ,(powerful ) blue leds (440-470 nm ) and
maybe -just maybe -a bit of FR leds ,especially during flowering....
(maybe deactivation or dimming 660s' a bit-during flowering ,will also increase flowering rates...)
Greens (500-599 nm )-if any through utilisation of NW (4500-5500 K ) leds-,at this case should stay close to 10-15 % ...No more...
You feed the girls a reasonable amount of a complete diet and they do just fine.
You over feed and they turn into fat gluttonous picky bitches and/or
they are squinting their little eyes and can only take advantage of the blue and red?
To me sun adapted plants get fed past full and have to make adaptations to limit or protect from being over amped. (literally)
Does this make more bio mass, yes. do these plants transpire more, yes.
Do sun adapted plants make bigger and better flowers??????
I know one thing, electricity is not cheap and shade adapted is the only way to go.
i need help i want to buy 1w led chips from ebay but not sure what color ratio to get. i want a single panel to do both veg and flowering if possible. i want to use a total of 40watts to cover a very small grow space. its probably 2x2x3. so not too much to light it hopefully. im only going to be growing 4 to 5 inch tall plants in solo cups. please any info is helpful
SDS what are your plans when the temp go even more down ?
Are you going to leave it as it is ? Do you think that low temps (17 and below) are going to affect flowering ? ( airy buds for example ? )
Cool temperature response
In addition to classic vernalisation responses, there are many reports of species, especially from warm climates where near-freezing temperatures are infrequent, which flower if exposed to temperatures from 10°C to 20°C. For some tropical fruit crops (e.g. mango, avocado, lychee, longan), especially those grown in the subtropics (latitude 23°–30°) where substantial seasonal temperature changes occur, floral induction results from exposure to night temperatures of 10–15°C. Because tropical species are relatively under-researched compared with their temperate counterparts, physiologists have yet to decide whether these cool responses have similar mechanisms to temperate vernalisation but are adapted to a different temperature range. Another possibility is that flower initiation and development are blocked/reversed by higher tempera-tures, so low temperature could merely be a passive condition permitting expression of an innate capacity to flower. This may be the case for Acacia and rice flower (see King et al. 1992) but for Pimelea ferruginea, which flowers if exposed to temperatures below a daily average of 16–18°C for ﬁve to seven weeks, the response is inductive and higher temperature does not cause loss of developing flowers (King et al. 1992).