Plants need light to make sugars through photosynthesis, but not all colors of light affect growth in the same way. A school project using red, blue, green, and white LED lamps lets students test how light color changes plant height, leaf count, and overall health. This matters because light color is used in greenhouses, indoor farms, and plant research.
A fair test helps separate real plant responses from random differences between seedlings.
Key Facts
- Independent variable: light color, such as red, blue, green, or white.
- Dependent variables: plant height, leaf count, leaf color, and overall plant health.
- Controlled variables should include plant species, soil type, pot size, water amount, light distance, and light exposure time.
- Growth rate = change in height / change in time.
- White light contains many wavelengths, while red and blue LEDs provide narrower wavelength ranges.
- Chlorophyll absorbs red and blue light strongly and reflects much of the green light.
Vocabulary
- Photosynthesis
- Photosynthesis is the process plants use to convert light energy, carbon dioxide, and water into glucose and oxygen.
- Wavelength
- Wavelength is the distance between repeating parts of a light wave and is related to the color of visible light.
- Chlorophyll
- Chlorophyll is the green pigment in leaves that absorbs light energy for photosynthesis.
- Independent variable
- The independent variable is the factor a student changes on purpose to test its effect.
- Controlled variable
- A controlled variable is a factor kept the same so the experiment is a fair comparison.
Common Mistakes to Avoid
- Changing both light color and brightness at the same time is wrong because you cannot tell which factor caused the growth difference.
- Using different plant sizes at the start is wrong because taller or healthier starting plants may grow differently for reasons unrelated to light color.
- Measuring only at the end is wrong because weekly data show growth patterns and help identify problems such as wilting or sudden changes.
- Putting lamps at different distances is wrong because light intensity changes with distance and can strongly affect photosynthesis.
Practice Questions
- 1 A bean plant under blue light grows from 6 cm to 18 cm in 4 weeks. What is its average growth rate in cm per week?
- 2 A student counts leaves on four plants after 3 weeks: red light 14 leaves, blue light 18 leaves, green light 9 leaves, and white light 16 leaves. What is the mean number of leaves, and which light color produced the most leaves?
- 3 A plant under green light grows less than a plant under blue light even though both lamps have the same intensity and exposure time. Explain why this result makes sense using chlorophyll absorption.