A botanist wants to see how different colored light waves influence the growth of pea plants. She puts the same number of seeds into three identical pots with the same kind and amount of soil. she then gives them the same amount of water every three days for the length of the experiment. One pot is placed into a dark windowless closet. Another pot is left on the windowsill, and the third is placed under a lamp with a green bulb. she records the height of each plant every day for three months. What is the independent variable in this experiment?