Final answer:
The filling of a light blue tube depends on the specific instructions of a chemistry experiment.
Step-by-step explanation:
In the context of the question, the light blue tube refers to a test tube used in a chemistry experiment. Whether or not it needs to be completely filled depends on the specific instructions of the experiment. In some cases, the tube may need to be completely filled to ensure accurate measurements or proper functioning of the experiment. In other cases, the tube may only need to be partially filled, as indicated by phrases such as 'about one third full' or 'partially filled.'