A student investigated the effect of colour of light on the rate of photosynthesis in leaves. Figure 9 shows how the investigation was set up. Give one way the student could change the colour of the light shining on the leaf discs.

White light is a mixture of all the colours of the visible spectrum. To get a specific colour of light, you need to block out the other colours. This can be achieved by placing a coloured filter in front of the white light source (the lamp). For example, a red filter will absorb all colours except red, allowing only red light to pass through and shine on the leaf discs. Similarly, a blue filter would be used for blue light, and so on.