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Light requirements for indoor plants

Technology and engineering is a prominent part of our everyday life. Therefore it is vital that children and young people are acquainted with it from an early age, and this preferably in an integrated way in the various school subjects. In this example for pupils in years 5 and 6 of primary school and the first two years of secondary education, we combine physics, technology, engineering, research skills and problem solving skills. We depart from the question: What does a plant need to grow indoor?. We aim for children to build a spectrometer and use it to explore and compare various light sources. For the construction of the spectrometer, we encourage schools to use recycled materials only.


What do plants need?

Too often pupils are offered answers in the form of theory without practice or application. In this project, we turned it around. We ask primary school children: What do plants need to grow indoor in winter?. The answers varied from water and earth to fertilizer and light. Then we asked the children what kind of light source would be most suitable. They children displayed some uncertainty but indicated the need to look for a light source like that sun. The aims of this project are threefold: (1) to allow the children to become familiar with the concepts light and colour; (2) to allow them to draw up the results in a technical drawing and (3) to allow them to carry out qualitative research with an instrument.

Build your own spectrometer

In order to compare the different light sources (LEDs, coloured lightbulbs, energy saving lightbubls, TL-tubes, the sun,...) we suggested to build a spectrometer. A spectroscope or spectrometer is an instrument that breaks light up into its different colours and make the spectrum visible. This is the visible spectrum (e.g. a rainbow being the rays of sunlight broken up by raindrops and forming the visible spectrum in the shape of a rainbow). For more information about the spectrum, please visit wikipedia.

The only material needed to build a simple spectrometer is a cornflakes boxes, a DVD, aluminium foil, glue and some tape. Cost per pupil: € 0!

From technical drawing to realisation

In order to build the spectrometer, we let the pupils interpret a technical drawing and copy it on squared paper. Our [technical drawing of the spectrometer includes the dimensionless sizes. Therefore children can choose the scale of their instrument freely: number 3 can mean 3 cm, 6 cm of 3 squares, etc. The exact measurements are unimportant, as long as the relative measurements are correct. Pupils copied the map on squared paper in groups of 4.

Once the technical drawing is copied to the preferred size successfully, it is glued onto a piece of thin cardboard (a cornflakes box is ideal). Then the spectrometer can be cut out. It is important to only cut on the full lines. The dotted lines are folding lines!

Folding the card on the dotted lines, you will have made a box. Two pieces of aluminium foil are put in place on the inside of the box, covering the rectangular opening of the box (2 by 1.5), so that there is a very thin opening between the two. The square space (2 by 2) is covered with a piece of DVD. It is advisable for an adult to cut the DVD up and split it in two: the part with the foil is used for the spectrometer with the shiny side on the inside of the box. Here too, the foil is glued to the inside of the box. The foil of the DVD is fragile. For the best result, it is best not to touch it.

Spectrometer

When the aluminium foil and piece of DVD are in place, the box can be closed. It is vital that there are no openings, through which light can enter. When the spectrometer is completed, the piece of DVD will be at an angle of 45 degrees in relation to the opening.

Comparing different light sources

The spectrometer is now ready for use. The slit can be pointed at a light source while the pupils look through the piece of DVD foil. For reasons of safety, the spectrometer should never be pointed at the sun – this can cause serious eye injury! We asked the pupils to do and investigate different light sources by themselves, and to draw the observed spectrums. The pupils received a form. to fill out. What light source best resembles that of the sun?

It is important to allow the pupils to decide for themselves how to note their observations. While most used coloured pens, some used descriptions (This can be observed in the film at the top of this page). In our test-class, the pupils using colours, made the most accurate observations. Of course, this does not need to be the case with your pupils.

Evaluation and discussion

Following their investigation the pupils gathered and described their findings. It was our aim to encourage them to understand that white light consists of a variety of colours. Most observed the differences in colours with the red light showing only red/orange spectrum and day light displaying the full spectrum of the rainbow. Some pupils also noticed a difference between a continuous spectrum (think lines flowing into one another – light bulb) and a line spectrum (fine and intense lines – energy saving light bulb). The group can then decide which is the ideal light source for the plant.

Trouble shooting

The spectrum lines are horizontal instead of vertical: The slit of the aluminium foil need to be turned by a quarter rotation

The spectrum of a TL-tube does not show lines but vague dots: There is light leaking into the box OR the slit is too wide

Thank you

This project was developed in co-operation with Jesse Bouman. The film was recoded in the class of Miss Nathalie in De Weg-Wijzer Primary in Evere, Belgium.