A null hypothesis is the prediction a researcher hopes to prove false. The null hypothesis for our study would be: 'There will be no difference in test scores between the different amounts of light.' The focus of our null hypothesis is on what we are studying: the tests. When we write our null hypothesis, we are expecting the focus of our study, the test scores, to be unaffected by what we are manipulating: the light levels. The null hypothesis doesn't need to be an if-then statement. It basically says nothing is going to happen in our experiment or that there is no connection between the different parts of the hypothesis.
Experimental methods are used to demonstrate causal relationships between variables. In an experiment, the researcher systematically manipulates a variable of interest (known as the independent variable) and measures the effect on another variable (known as the dependent variable). Unlike correlational studies, which can only be used to determine if there is a relationship between two variables, experimental methods can be used to determine the actual nature of the relationship. That is to say that if changes in one variable actually cause another to change.