To investigate the effect of different light sources on plant growth.
Background
information
Plants are always at the very bottom of food chains.
This is because of their ability to make food for themselves.
To be exact, plants utilise light to convert water (H2O)
and carbon dioxide (CO2)
into oxygen (O2) and carbohydrates, mainly sugar.
This process is called photosynthesis.
The formula is the following:
6CO2
+ 6H2O + (light) = C6H12O6 + 6O2
The purpose of this experiment was to investigate if the type
of light source had an observable difference on a plant’s photosynthetic
process. Also, this experiment would reveal if natural products were
truly better then their artificial counterparts.
Chlorophyll is the pigment of plants that convert light into chemical
energy. Three factors contribute to
how chlorophyll reacts to light includes: quantity, quality, and duration.
Light Quantity
This refers to the concentration or intensity of light.
This can be measured in “foot candles”.
Two factors affect this: distance and angle from the source.
The latter is why the intensity of natural sunlight fluctuates throughout
the seasons. Distance is an
important factor for artificial lights. When
growing plants under artificial lights, the plant must be place 2-6 inches away
from the light. Up to a certain
point, increasing the light intensity will result in the plant having a greater
capacity for producing food through photosynthesis.
Manipulating the light intensity without changing these factors is
possible as well. Woven
shade-cloths can be used to decrease the light intensity.
Placing reflective material around an object will result in an increase
of light intensity.
Light Quality
Light quality refers to the wavelength, or colour, of light. This can be measured using the “Kelvin Scale” or the “Colour Rendering Index” (CRI). The Kelvin scale basically gives colours a measurement called a “colour temperature”. The longer the wavelength (i.e. the lower the frequency) of a colour the lower its colour temperature would be. For example, red has wavelengths ranging form 630 to 760 nanometres and it has a colour temperature of 2000K. A nanometre is a billionth of a meter. The CRI is basically a percentage that compares the colours that an artificial light emits with natural sunlight. Anything with a CRI greater than 90 is considered to be “full spectrum."
Light Duration
Light duration refers to the amount of time that a plant is exposed to light. Like light quantity, this varies with the seasons for sunlight. It was initially thought that periods of light triggered floral growth, but in actuality, it is the amount of uninterrupted darkness that is crucial in triggering flowering. The response that plants have towards light and dark is called “photoperiodism”. Plants can be classified into three categories based on this data.
I. Short Day
These plants must have less than 12 hours of light duration in a day for them to flower.
II. Long Day
These plants require more than 12 hours of light duration in a day for them to flower.
III. Day Neutral
These plants form flowers regardless of the amount of light duration, as long as there is enough to maintain normal plant growth.
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