I am going to offer you a few suggestions for this resarch proposal, it is up to you to pick the ones that are more convenient for you.
You can use different light sources, such as incandescent, fluorescent, sunlight, and total darkness. Be sure to keep the amount of time of exposure to light the same for all light sources. You can grow beans or any other easy to grow plant, and inspect them every 12 hours or so. Or you can see how many beans will germinate under each light variable. Be sure to have no variables other than the light source. Even the amount of water and the watering schedule has to be constant. Soil should be the same and the type of pot and seed and number of seeds per pot that you use should also be the same.
If you chose to grow plants rather than to germinate seeds, be sure to include qualitative data as well as quantitative, by this I mean, not only do you measure the growth of each plant and the length and width of each leaf, but also you may want to count the leaves and describe their color, the appearance of the stalk and so on.
Remember the if and then statement for your investigative question. If bean plants are grown under various light sources, then bean plants will grow at different rates under different light sources.
The purpose of your experiment is to investigate the effect of different light sources on the growth of bean plants.
I suggest you plant at least 10 beans per light source. This would give you about 40 plants, if all germinate. If not all germinate, I suggest that you even out the numbers once they have grown enough to keep their leaves off the soil. If you have only 6 that germinate for lets say the incandescent light, then you should reduce all others to 6 once you have established that they are healthy. Once again this eliminates having more variables.
Your title should reflect the purpose of your experiment so The effect of different light sources on the growth of bean plants seems appropriate as it is short and to the point.