HOW LONG DO YOU KEEP A GROW LIGHT ON?

Plants need light to flourish and thrive. Sunlight is enough to sustain a plant’s daily light requirement, but what if you want to grow it inside your home?

Some people prefer growing plants indoors because it’s easier to control the environment. However, there’s a learning curve in using a grow light for sheltered plants. (1)

In essence, both light and dark are important in a plant’s growth cycle. (2) Photosynthesis happens in light while respiration, a process of breaking down photosynthetic products for growth, happens at night. (3)

As a rule of thumb, an indoor plant needs 12-16 hours of light exposure per day. (4)

CAN TOO MUCH LIGHT KILL PLANTS?

Too much of a good thing is bad, and this applies to light in plants.(5)They naturally crave illumination, but receiving plenty of light energy at a fast rate causes them to convert it to chemical energy ineffectively. (6)

The common notion is that all types of light can be detrimental to a plant if exposed too much. However, three significant factors—light spectrum, intensity and duration—will ultimately determine the plight of indoor plants. (7)

Light from the blue and red ranges of the spectrum is required for foliage growth and blooming, respectively. (8)This means that, as tempting as fancy light systems are to buy, not all of them can help a plant flourish well.

 

As for intensity, which is the light’s strength in foot-candles, the optimal amount depends on the type of plant you are growing. (9) Full sunlight ranges from 10,000-12,000 foot-candles, which is the brightest but also the hardest to achieve indoors. (10)

 

Light duration specifies how many hours of light a plant is subjected per day. Indoor plants need longer exposure to obtain the required intensity. (11) Flowering plants can be exposed to around 16 hours, whereas green leafy houseplants can settle for 12 hours of light. (11)

 

Too much of each factor can ultimately lead to plant death.

 

 

CAN YOU LEAVE GROW LIGHTS ON FOR 24 HOURS?

 

People often misconceive light as a 24-hour commodity for plants. Nothing could be more wrong. Light is indispensable, (12) but it does not necessarily mean that longer light duration equals greater yield. (13)

Photosynthesis, the specialized plant process that allows it to thrive, is comprised of two phases: light reaction and the dark reaction. (14)

In the light reaction process, light is absorbed and transformed into volatile chemical energy. The dark reaction phase can occur without light and at any time, (15) but it is triggered primarily by darkness. Think of it as the circadian rhythm—the absence of light is nature’s signal for living things to rest and get ready for the next day.

While you can leave the grow light on for 24 hours, it will disturb the plant’s respiration, and thus alter the normal growth pattern. (16)

 

WHAT HAPPENS WHEN PLANTS ARE EXPOSED TO TOO MUCH LIGHT?

 

When the light becomes too much, a phenomenon called photooxidative stress occurs. (17)This generates reactive oxygen species or the free radicals, that may damage the plant.

 

In most cases, plants can repair and adapt to changes in light and other environmental factors. They have effectual regulatory systems that allow them to thrive in the face of stress. (18)

 

In simple terms, the most obvious manifestation of too much light in plants is leaf burning. This causes the yellowing of the leaf part where light exposure is great. Nevertheless, the veins inside will still look green. (19)

 

Too much light also exposes the plant to more heat energy, which can lead to wilting. This it’s also a big factor in nutrient deficiency in plants, particularly since more heat increases water requirement. (20)

 

When your plant is subjected to harsh grow light, expect these cascading effects that can lead to plant death if left untreated.

 

 

 

REFERENCES

 

1 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3949401/. Photosynthesis under artificial light: the shift in primary and secondary metabolism

2 https://naldc.nal.usda.gov/download/IND43966624/PDF Further studies in Photoperiodism, the response of the plant to relative length of day and night

3-https://www.sciencedirect.com/science/article/abs/pii/0003986163905472 Photosynthesis and respiration

4-https://www.researchgate.net/publication/293049370_The_effect_of_photoperiodism_with_LED_light_on_productivity_of_female_flower_in_cucumber_Cucumis_sativus_L

5-https://www.ncbi.nlm.nih.gov/pubmed/1566330 Too much of a good thing: light can be bad for photosynthesis

6-http://www.plantphysiol.org/content/125/1/29 When there is too much light

7-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2649303/ Plants in light

8-https://www.actahort.org/books/956/956_41.htm Finding the optimal growth-light spectrum for greenhouse crops

9-https://www.jstor.org/stable/2435785 The Influence of light intensity and light quality upon growth of plants

10-https://extension.illinois.edu/houseplants/needs_light.cfm Houseplant needs

11-https://www.hort.vt.edu/ghvegetables/documents/GH%20Lighting/Light%20in%20the%20Greenhouse_JBrown.pdf Light in the Greenhouse: how much is enough?

12-https://www.jstor.org/stable/4440225Light and hormones in plant development

13-http://www.globalsciencebooks.info/Online/GSBOnline/images/2010/PS_4%281%29/PS_4%281%295-17o.pdf Plants under Continuous light: a review

14-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5264509/ Photosynthesis

15- https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/5%3A_Microbial_Metabolism/5.12%3A_Biosynthesis/5.12C%3A_The_Calvin_Cycle

16-https://www.ncbi.nlm.nih.gov/books/NBK22376/ The activity of the Calvin cycle depends on environmental conditions

17-https://setac.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1399-3054.1994.tb03042.x Photooxidative stress in plants

18-http://www.academicjournals.org/app/webroot/article/article1380900919_Anjum%20et%20al.pdf Morphological, physiological and biochemical responses of plants to drought stress

19-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4454199/ Plant tolerance to excess light energy and photooxidative damage relies on plastoquinone biosynthesis

20-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5800372/ Rapid responses of plants to temperature changes