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What Wavelengths and Colors do

To understand how your crops are going to react on different wavelengths and colors, you have to keep in mind that every crop and every growth stage requires an individual approach.

LED Grow Light Absorption curves of plants

The amount of light affects the photosynthesis process in the plant.

This process is a photochemical reaction within the chloroplasts of the plant cells in which CO2 is converted into carbohydrate under the influence of the light energy.

The spectral composition of the different wavelength regions (blue, green, yellow, red, far red or invisible e.g. UV or IR) is important for the grows, shape, development and flowering (photomorphogenesis) of the plant.

For the photosynthesis, the blue and red regions are most important.

The timing / light duration which is also called photoperiod is mainly affecting the flowering of the plants. The flowering time can be influenced by controlling the photoperiod.

Photosynthetic efficiency is mainly driven by chlorophyll a and b.
Chlorophyll a and b are mainly responsible for the photosynthesis and responsible for the definition of the area for the photosynthetically active radiation PAR.

The Photosynthetically active radiation (PAR) shows further photosynthetic pigments also known as antenna pigments like carotenoids - carotene, zeaxanthin, lycopene and lutein etc.

Different regions of the wavelength in the illuminaton spectrum have different effects on the plants:
Wavelength range [nm]PhotosyntesisFurther EffectsFurther EffectsFurther Effects
200 – 280
Harmful

280 – 315
Harmful

315 – 380



380 – 400Yes


400 – 520YesVegetative growth

520 – 610SomeVegetative growth

610 – 720YesVegetative growthFloweringBudding
720 – 1000
GerminationLeaf building and growthFlowering
> 1000
Converted to heat

The Phytochromes Pr (red) and Pfr (far red) are mainly influencing the germination, plant growth, leave building and flowering.

The phytomorphogenic effects are controlled by applying a spectrum with a certain mix of 660nm and 730nm in order to stimulate the Pr and Pfr phytochromes.



A typical application example for the use of 730nm: The shade escape reaction

LED Grow Light Shade escape reaction of plants

One of the most obvious influence of far red light on a plant is the shade escape reaction.

Illumination with 660nm:

If the plant is illuminated mainly with 660nm it feels like illuminated in the direct sun and grows normally.

Illumination with 730nm:

If the plant is illuminated mainly with 730nm it feels like growing in the shadow of another plant that shades the sun light.

Therefore the plant is reacting with an increased length growth to escape the shadow. This leads to taller plants but not necessarily to more bio mass.

Special potential of LEDs in floriculture lighting


Traditionally ornamental plants are of high economic importance. The Red and Far-Red light mediates the conversion of phytochromes which can control the triggers for flowering.

Signal Transduction in plants

Illumination with 730nm:

The cycle from Pr to Pfr is initiated by red light of 660nm which represents daylight. During the night time, the Pfr is converted back to Pr. This back conversion can also be actively be influenced by 730nm far red light.

This enables a perfect control of the flowering timing independent of the seasons.



Control of the flowering due to control of the critical day length by using any light


Due to the influence of the Pr and Pfr ratio the flowering can be controlled to adjust the timing to environmental or seasonal requirements.

LED Grow Light Critical day length

Effect of red light around 660nm on physiology of vegetables
PlantRadiation sourceEffect on plant physiology
Indian mustard (Brassica juncea L.) Basil (Ocimum gratissimum L.)Red (660 and 635 nm), LEDs with blue (460 nm)Delay in plant transition to flowering as compared to 460 nm + 635 nm LED combination
Cabbage (Brassica olearacea var. capitata L.)Red (660 nm) LEDsIncreased anthocyanin content
Baby leaf lettuce (Lactuca sativa L. cv. Red Cross)Red (658 nm) LEDsPhenolics concentration increased by 6%
Tomato (Lycopersicum esculentum L. cv. MomotaroNatsumi)Red (660 nm) LEDsIncreased tomato yield
Kale plants (Brassica olearacea L. cv Winterbor)Red (640 nm) LEDs (pretreatment with cool white light fluorescent lamp)Lutein and chlorophyll a, b accumulation increased
White mustard (Sinapsis alba), Spinach (Spinacia oleracea), Green onions (Allium cepa)Red (638 nm) LEDs with HPS lamp (90 μmol m-2 S-1), total PPF (photosynthetic photon flux) maintained at 300 μmol m-2 S-1Increased vitamin C content in mustard, spinach and green onions
Lettuce (Lactuca sativa), Green onions (Allium cepa L.)Red (638 nm) LEDs and natural illuminationReduction of nitrate content
Green baby leaf lettuce (Lactuca sativa L.)Red (638 nm) LEDs (210 μmol m-2 S-1) with HPS lamp (300 μmol m-2 S-1)Total phenolics (28.5%), tocopherols (33.5%), sugars (52.5%), and antioxidant capacity (14.5%) increased but vitamin C content decreased
Red leaf, green leaf and light green leaf lettuces (Lactuca sativa L.)Red (638 nm) LEDs (300 μmol m-2 S-1) with HPS lamp (90 μmol m-2 S-1)Nitrate concentration in light green leaf lettuce (12.5%) increase but decreased in red (56.2%) and green (20.0%) leaf lettuce
Green leaf ‘Lolo Bionda’ and red leaf ‘Lola Rosa’ lettuces (Lactuca sativa L.)Red (638 nm) LEDs (170 μmol m-2 S-1) with HPS lamp (130 μmol m-2 S-1)Total phenolics and α-tocopherol content increased
Sweet pepper (Capsicum annuum L.)Red (660 nm) and farred (735 nm) LEDs, total PPF maintained at 300 μmol m-2 S- 1Addition of far-red light increased plant height with higher stem biomass
Red leaf lettuce ‘Outeredgeous’ (Lactuca sativa L.)Red (640 nm, 300 μmol m-2 S-1) and farred (730 nm, 20 μmol m- 2 S-1) LEDs.Total biomass increased butanthocyanin and antioxidant capacity decreased
Red leaf lettuce ‘Outeredgeous’ (Lactuca sativa L.)Red (640 nm, 270 μmol m-2 S-1) LEDs with blue (440 nm, 30 μmol m-2 S-1) LEDsAnthocyanin content, antioxidant potential and total leaf area increased
Tomato seedlings ‘Reiyo’Red (660 nm) and blue (450 nm) in different ratiosHigher Blue/Red ratio (1:0) caused reduction in stem length



Effect of blue light around 450nm on physiology of vegetables
PlantRadiation sourceEffect on plant physiology
Cherry tomato seedlingBlue LEDs in combination with red and green LEDs, total PPF maintained at 300 μmol m-2 S-1Net photosynthesis and stomatal number per mm2 increased
Cabbage (Brassica olearacea var. capitata L.)Red (660 nm) LEDsIncreased anthocyanin content
Seedlings of cabbage (Brassica olearaceavar. capitata L.)Blue (470 nm, 50 μmol m-2 S-1) LEDs aloneHigher chlorophyll content and promoted petiole elongation
Chinese cabbage (Brassica camprestis L.)Blue (460 nm, 11% of total radiation) LEDs with red (660 nm) LEDs, total PPF maintained at 80 μmol m-2 S-1Concentration of vitamin C and chlorophyll was increase due to blue LEDs applicatio
Baby leaf lettuce ‘Red Cross’ (Lactuca sativa L.) Blue (476 nm, 130 μmol m-2 S- 1) LEDsAnthocyanin (31%) and carotenoids (12%) increased
Cucumber ‘Bodega’ (Cucumis sativus ) and tomato ‘Trust’ (Lycopersicon esculentum)Blue (455 nm, 7-16 μmol m-2 S- 1) LEDs with HPS lamp ( 400- 520 μmol m-2 S-1)Application of blue LED light with HPS increased total biomass but reduced fruit yield
Transplant of cucumber ‘Mandy F1’Blue (455 and 470 nm, 15 μmol m-2 S-1) with HPS lamp (90 μmol m-2 S-1)Application of 455 nm resulted in slower growth and development while 470 nm resulted in increased leaf area, fresh and dry biomass



Effect of green light around 520nm on physiology of vegetables
PlantRadiation sourceEffect on plant physiology
Red leaf lettuce (Lactuca sativa L. cv Banchu Red Fire) Green 510, 520 and 530 nm LEDs were used, and total PPF was 100, 200 and 300 μmol m-2 S-1 respectivelyGreen LEDs with high PPF (300 μmol m-2 S-1) was the most effective to enhance lettuce growth
Transplant of cucumber ‘Mandy F1’Green (505 and 530 nm, 15 μmol m-2 S-1), LEDs with HPS lamp (90 μmol m-2 S-1)505 and 530 nm both resulted in increased leaf area, fresh and dry weight
Red leaf lettuce (Lactuca sativa L. cv Banchu Red Fire)Green 510, 520 and 530 nm LEDs were used, and total PPF was 100, 200 and 300 μmol m-2 S-1 respectivelyGreen LEDs with high PPF (300 μmol m-2 S-1) was the most effective to enhance lettuce growth
Tomato ‘Magnus F1’ Sweet pepper ‘Reda’ CucumberGreen (505 and 530 nm, 15 μmol m-2 S-1) LEDs with HPSlamp(90 μmol m-2 S-1)530 nm showed positive effect on development and photosynthetic pigment accumulation in cucumber only while 505 nm caused increase in leaf area, fresh and dry biomass in tomato and sweet pepper
Transplant of cucumber ‘Mandy F1’Green (505 and 530 nm, 15 μmol m-2 S-1), LEDs with HPS lamp (90 μmol m-2 S-1)505 and 530 nm both resulted in increased leaf area, fresh and dry weight



Horticulture Lighting Example LED light ratios for different purposes
General purpose – high efficiencyHorticulture Grow Light General purpose high efficiency
TypeWavelengthmW Ratio
LD Cxxx450nm23%
LH Cxxx660nm77%
The highest efficacy of μmol/J from the spectrum can be achieved by using the 660nm Red LEDs combined with some 450nm Blue LEDs to maintain a reasonable ratio between the wavelengths.
Vegetative GrowthHorticulture LED Grow Light Vegetative Growth
TypeWavelengthmW Ratio
LD Cxxx450nm50%
LH Cxxx660nm50%
Especially for growth of the leafy green vegetable plants the vegetative growth ratio is used to achieve fastest growth where visible assessment of plant health is not important.
Best for seedlingsHorticulture LED Grow Light Best for seedlings
TypeWavelengthmW Ratio
LD Cxxx450nm75%
LH Cxxx660nm25%
A high blue content in the spectrum is recommended for growth of the seedlings.
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