1. Introduction


Background Research

Plants are autotrophic, which means they make their own food, sustaining life without needing to consume other organisms. They do this through the process of photosynthesis. This is where light energy from the sun (or other radiant source) is trapped by green plants and transformed into chemical energy.

All photosynthetic organisms contain chlorophyll, a green pigment found in chloroplasts. Chlorophyll is responsible for the process of photosynthesis. It is green as a result of reflecting green light rays. Light energy is captured by chlorophyll and used to form ATP molecules, which are in turn used as an energy source by plants in a chemical reaction with combines carbon dioxide and water to produce glucose and oxygen. The equation which describes the process of photosynthesis is:

                                           (Light energy+ Chlorophyll)
Equation: Carbon dioxide + water ► glucose + water + oxygen

The relationship between light and plant growth can be demonstrated by exposing leaves to various colors of light. Light supplies the energy to carry on photosynthesis, the food-making process in leaves. All light, including sunlight, have a range of wavelengths. The shorter a light wavelength, the more energy it has. However, leaves contain specific types of pigments to absorb light energy. only certain wavelengths of light can be absorbed by pigments such as chlorophyll, hence plants can only make use of energy from light absorbed by these pigments.

For example, green leaves contain the pigment chlorophyll which reflects green light (so leaves appear green), therefore plants with green leaves cannot make use of light energy from green light. Chlorophyll absorbs light of wavelength 664nm best, and the wavelength of red light is between 620nm - 740nm, hence plants with chlorophyll can make use of light energy from red light the best.

Leaves also  contain pigments other than chlorophyll such as carotenoids and phototropins. Carotenoids consist of xanophylls and carotenes. Carotenoids are also yellow, orange, and red pigments. In general, carotenoids absorb wavelengths ranging from 400-550 nanometers and the key role that they serve is to protect chlorophyll from photodamage. Since carotenoids are red pigments, they reflect red light and do not absorb it at all. Instead, carotenoids absorb blue light, and protects the chlorophyll from photo damage.

Phototropins are blue light receptors for phototropism(orientation of a plant in response to light), chloroplast movement, leaf expansion, and stomatal opening. Although blue light is not the best colour of light for the process of photosynthesis itself, it improves the process through chloroplast movement and stomatal opening. Therefore, blue light is better for the growth of plants instead of actual photosynthesis itself, which can be seen through leaf expansion.

Through our research, we can conclude that red light is the best for the process of photosynthesis in plants, while blue light is the best for the growth of plants. This is why blue and red light are the best colours of light for plants. Our project is about how different coloured lights affect plant growth, so our experiment should show that blue light is the best, followed by red light.

Problems with farming and how we can help

Plants are an essential part of the food chain required by all living things to survive. The growing world population and subsequent alteration to the natural environment has placed increased pressure on available plant resources. This is particularly evident in the area of agriculture, where optimum crop productivity is important to meet the increased demand for food by the growing world population.

Knowing optimum light conditions to maximise photosynthesis and therefore plant growth rate could be considered useful information, especially to those involved in agriculture.

It can help them grow crops more efficiently and allow them to have a better harvest. In countries that don’t receive a lot of sunlight such as Norway, greenhouses are often built to grow crops even in bad weather. Therefore, we propose using blue and red light which is the wavelength of light absorbed by chlorophyll and this will help farmers to grow crops faster and obtain healthier plants. In order to achieve this, farmers will require light bulbs that emit specific wavelengths to provide light for photosynthesis.
Question being addressed

To determine the optimum range of wavelengths of light conditions in order to maximise photosynthesis and therefore plant growth rate could be maximised in agriculture. Since there are a variety of pigments present in leaves of plants, we wanted to find out how different coloured light affects the growth of 3 types of plants with 3 different coloured leaves. We can then use our findings to improve and innovate urban farming .

Independent Variable:
  • Colour of light
  • Types of plants

Dependent Variable:
Height of Plant Growth

  • Intensity of light must be the same for every plant
  • Amount of water given to each type of plant must be the same
  • Amount of air in the surroundings must be the same
  • Same type of soil should be used to ensure that the amount of nutrients is the same


From our background research, we concluded that exposure of plants to blue light and red light will result in the fastest rate of photosynthesis and hence the greatest plant growth. Green light is least effective because of the reflection of green light due to the green pigment of the chlorophyll.  Therefore, the plants should grow best under blue light and red light followed by yellow light, and lastly, green light.

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