If the light source is closer to the Elodea, intensity will be greater, then the rate of photosynthesis should increase, and I will see more bubbles. Proving or disproving their hypothesis will depend on their experimental set-up. Students should observe that the closer the light is to the plant the more bubbles they should see. The more bubbles, the faster the rate of photosynthesis. You can have students attempt to quantify the amount of oxygen produced by encouraging them to modify their experiment to trap the oxygen and determine its volume.
Intensity can change due to filtering or blocking of light by the atmosphere or water.
Worlds that are farther away from the Sun than the Earth may receive too little light to power photosynthesis. The moon is about as close to the Sun as the Earth is, and therefore the intensity of light should be similar. Explain your answer. If light intensity was the only factor that influenced habitability one might expect photosynthetic life. But the lack of liquid water and atmosphere are greater limiting factors than the intensity of light.