Projects on coloured light's effect on plant growth

Written by lela lake
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Projects on coloured light's effect on plant growth
Study the effect of lights on plant growth with simple do-at-home experiments. (sprout image by Evgeniy Mitroshkin from

Studying the effects of different colour lights on plant growth is a popular science fair project. Experiments range from simple projects with using everyday items to more complex approaches requiring minor construction and special equipment. Most strategies use coloured gels or cellophane to project diffused coloured light on plants in a controlled environment. Coloured light bulbs can be added for more complex effects. Regular documentation of the plants exposed to different coloured lights is crucial for a successful experiment.

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Windowsill experiment

Poke small holes in the bottom of four large styrofoam cups for drainage. Fill cups with equal amounts of soil. Plant one lima bean seed in the centre of each cup, tamp it down gently with a spoon and water. Stick a wooden lolly stick or straw into the soil next to the bean seed.

Fashion a tent-like cover over the lolly stick out of a 30 cm (1 foot) square of coloured cellophane using a different colour for each cup -- red, green, blue and yellow -- and tape the edges to the cup. Be sure to leave space for air and water to enter.

Place all four cups on a windowsill that receives regular sunlight. Water lightly every day.

Draw a chart with a category for the different colours. Measure and record each plants' growth and health once a week. If possible, take a picture of each plant once a week so you can visually compare their growth.

After one to two months of growth, compile results into a report that documents the effects of different coloured light filters on similar plants.

Aquarium experiment

This experiment uses soy beans that need to be germinated in seed pots one week before planting. While you wait for them to sprout, prepare the aquarium by adding soil to a depth of 12.5 cm (5 inches). Fertilise the soil, water it well and find a place where it will receive maximum sunlight.

Once the seedlings are transplanted in to the aquarium, take four differently coloured plastic transparencies that are available from office supply shops and form them into cones. Use cellophane tape to hold them in shape. Place a different coloured cone over each plant.

Water daily and record the growth rate of each plant on a chart. Note differences in height, health and growing patterns.

Indoor light experiment

Use four medium-size cardboard boxes without lids and turn them upside down. Use a utility knife to cut a window in the top and in each side a little smaller than a piece of regular A4 paper. Inside each box, tape five coloured page-sized plastic transparency sheets over each window all of the same colour. Make each box a separate colour. Red, green, blue and yellow are recommended.

Plant one lima bean each into five small pots filled with potting soil and water well. Place one pot into each of the four boxes and one on its own as the control to test the coloured light subjects against.

Set up five separate grow lights, either on stands or hanging over the boxes, so they shine through the coloured gels onto the plants. If desired, you can use coloured light bulbs and experiment with the different effects of light combinations. Use a regular grow light on the control plant outside the box.

Water daily and measure and record the growth rates and health of all plants. If various light bulbs are used, note any differences that occurred to the plants' growth as a result.

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