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Do Street Lights Affect Plants? The effects of light Pollution

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Plants need light to grow, among other vital inputs such as nutrients, soil, and water. Streetlights can alter a plant’s normal growth pattern by exposing the plant to more light than it needs.

Streetlights will affect plants by exposing them to unnatural light. Increased lighting periods can cause the plant to produce additional growth hormones as a natural response. These hormones can affect the rate and direction of which plants grow, as well as their ability to produce flowers and healthy fruits.

Streetlights illuminate our roadways and help us get to and from our destinations safely. However, it’s important to know that streetlights do have an impact on plants. Plants have many responses when it comes to light. These responses are dependent on the plant’s exposure to light.

In this article, we are going to discuss all the effects that street lights have on the growth and development of plants around the home.

Related articles on lights and its effects on plants –

How Porch Lights Affects Plants
What Causes a Leggy Monstera
The Benefits of rotating Potted plants
Bent plant leaves: Causes and Fixes
Why do Plant Stems Split? (Causes and Solutions)

Do Street Lights Affect Plants The effects of light Pollution
Street Lights

The Effects Street Lights Have on Plants

The first of the effects we will discuss is the effect that light pollution has on plants. As cities grow in population, so do their populations of street lights. 

The development of these streetlights occurs to ensure that more people can be reached by the roadway at any given time, but what benefits us may not have the same effect on the natural environment around us.

Here is a list of ways streetlights can affect plants:

1. It offsets Photoperiodism

The term photoperiodism is derived from two words: photo, meaning light, and periodism, meaning period.

The plant growth regulators are chemicals and physical factors that change the way plants grow. They affect the growth of both the roots and the shoots of the plant.

Photoperiodism is a process in which a plant responds to the duration of light or dark. It is a kind of biological clock. 

The duration of light and darkness affects the growth, development, and flowering of plants. 

During photoperiodism, plants also respond to seasonal changes in length of light or dark. 

For example, during summer, days are longer than nights which entice plants to flower and fruit, which is why most plants produce fruits during this period of the year.

2. Disrupts Flowering

The flowering of plants is very sensitive to light-dark conditions.

Plants that flower depend on cues from their environment to determine when to produce flowers. 

Too much light can lead to an extension of the vegetative stage, but generally, too little light will prevent flowering.

An international team of researchers has found that the protein, called cryptochrome 3, controls the circadian rhythm of plants and regulates their flowering time. 

A study done by Max Planck Institute, shows how the protein is activated by light and switches on the genetic program which leads to flowering.

3. Promotes Phototropism

Phototropism is the growth of an organism in response to a light stimulus.

During extended lighting periods, for instance, street lights can trick the plant into thinking that it’s receiving sunlight from the direction that the light is coming from.

This causes the plant to produce more Gibberellin.

Gibberellin, a growth hormone, is increased and increases stem growth. Gibberellin increases auxins in the tip of the shoots and roots, which promotes this growth. 

More light = more gibberellin = more growth

As a result, it increases legginess in plants as it promotes extra elongated growth towards the light. 

What you will notice is that the plant will start turning and growing towards the light and in its efforts in doing so it may start developing unnatural features such as the aforementioned legginess.

This symptom is more predominant in vined plants like monsteras and tomato plants.

4. Either Promotes or Stunts Growth 

Studies have found that blue light promotes the growth in plants as it causes the plant to produce more growth hormone. 

Therefore the amount of blue light a plant is subjected to will affect if it grows or becomes stunted.

Many of the lights that we use today produce a great deal of blue light such as the energy efficient LEDs.

LEDs are a great way to save energy if we are to use them in street lights or even for pathways.

Some of the brighter LED bulbs emit light in the 1000K to the 5000K range which can mimic close to daylight conditions.

Here are some light ranges and how they relate to light color temperature –

Color of LightColor intensityClassification
Soft White(2700K ? 3000K)Also known as Warm Light
Bright White/Cool White(3500K ? 4100K)Also known as Natural Light
Daylight(5000K ? 6500K)Also known as Cold Light

The spectrum of blue light increases as the color intensity increases.

The blue light in these spectrums can promote growth in plants if the light source emits a white or cold light. However, if the light is of warmer nature, it will emit a lesser amount of blue light which can reduce the growth in plants.

5. Reduces fruit production 

As we have explained above, light can disrupt flowering in plants.

The ripple effect of lack of flowering extends to less insects as their food supply diminishes. 

Insects such as bees and wasps will start looking elsewhere for their food as the plant produces little or not flowers. 

As a result the plant will also be affected as the pollination rate will reduce when there are little or no more insects around to carry out the process. 

Plants that can be affected by this are tomatoes, eggplants, ladyfingers, cucumbers and bell peppers.

6. Produces mutations

One simple example is a garden full of corn that I planted a couple years ago. It was exposed to a street light at night as well as normal sunlight during the day. 

To compare, I also planted another garden of corn (in another location) at the same time which was not exposed to any external light.

The street light was definitely as strong as the sunlight but it did have an effect on the way the plants grew and produced corn.

Here were the differences I found in both crops –

Corn plants that were exposed to the street light were 
Taller than the ones in the other location. 
The plants had sometimes splits on the barks.
The corn that were produced were larger and sometimes had two in one.
The kernels were sparsely populated in the corn.

Distance of the Street Light and the Effect on Plants

Can street lights affect plants

The effects of light on plant growth and development can be affected by the intensity of light because there is an inverse relationship between distance and light intensity ? as the distance increases, light intensity decreases. 

As the distance away from a light source increases, photons of light become spread over a wider area.

Therefore, the distance from the light source will have a direct effect on your plant.

Let’s take a 60 watt light source for example. If the light is located at 10 ft it will have a far greater effect on the plant than as if it were situated 20 or 30 ft away.

Although it might not seem as far, 20 feet away from a 100 Watt bulb can make a big difference.

So the further away the plant is from the light source, the less the light will affect the plant.

Light Sensitivity in Plants

Plants use light to create the food they need by absorbing light in the process of photosynthesis and lighting companies have used this fact to create lights that can provide the right conditions to maximise the process. 

[But there is something that they don?t tell you] Read on!

From studies done on how plants use lights for photosynthesis, it was shown that blue and red lights have the greatest effect on photosynthesis. 

In the experiment, a similar type of light was used for the same type of plant. The light was separated into different spectrum of wavelengths. Meaning that the different plants of the same type were exposed to the different colors of the spectrum.

The plants that were exposed to the blue and red light independently showed to have photosynthesized far greater than the plants that were not.

For this reason, many companies have capitalised and have created lights that mimic this experiment to create the perfect spectrum of light that maximises photosynthesis and hence greater plant growth.

Lights are then marketed based on this experiment to promote sales.

The catch: 

There is a reason that plants do well in full sunlight compared to if they are exposed to artificial lighting. 

With sunlight you have to do little to ensure that a plant grows well. 

Just provide good soil and some fertilizer. However with grow lights you have to continually be tweaking the conditions to ensure proper plant growth.

This is because sunlight exposes the plant to the full spectrum of light which the entire plant utilises for growth, not just blue or red light. 

A plant will also use the other lights in the spectrum to help promote biological processes which ensure their all round growth.

How Natural Light is Different from Artificial Lights

Natural Light ? Sunlight

Natural light (sunlight) provides light in the full spectrum for a fixed period of time during the 24 hour cycle. 

The daylight cycle is affected by the time of year where the tilt of the earth with respect to the sun produces the different seasons which we are accustomed to.

Therefore a plant will get less sunlight during the day at the beginning of spring than in the middle of summer (July-August months).

This change in light duration causes plants to produce fruits during longer periods of light and also causes them to go dormant in shorter periods such as winter.

Plants become accustomed to this type of seasonality and lighting and adjust their circadian cycle based on the seasons.

Artificial Lights ? Street Lighting

Outdoor lighting can produce similar lighting conditions to that of natural sunlight based on the type of lighting used. 

Solar lights are widely used to light pathways at night which primarily have LED bulbs built into them.

The Takeaway

Street lights are a necessity in our everyday lives, but it can have many negative effects when it comes to plants and the amount of light they receive.

A plant?s reaction to light is being altered by the increased lighting from street lamps, this will alter its overall growth pattern and direction. 

The overall growth and development patterns of the plant will be different than normal if too much light reaches the plant at any given time.

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