I wanted to know what grade you were in because I wouldn't want to point, say, someone in elementary school toward a resource they wouldn't understand.
If you are allowed to use anything, then I would start by looking up some of your keywords (type of light, plant growth) on google or ask.com.
Here is a really interesting review about the genetics of light-dependent plant growth, though it might be a little advanced for an eighth-grader:
Annual Review of Cell and Developmental Biology
Vol. 13: 203-229 (Volume publication date November 1997)
(doi:10.1146/annurev.cellbio.13.1.203)
LIGHT CONTROL OF PLANT DEVELOPMENT
Christian Fankhauser and  Joanne Chory Â
Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037; e-mail:
[email protected]
ABSTRACT
To grow and develop optimally, all organisms need to perceive and process information from both their biotic and abiotic surroundings. A particularly important environmental cue is light, to which organisms respond in many different ways. Because they are photosynthetic and non-motile, plants need to be especially plastic in response to their light environment. The diverse responses of plants to light require sophisticated sensing of its intensity, direction, duration, and wavelength. The action spectra of light responses provided assays to identify three photoreceptor systems absorbing in the red/far-red, blue/near-ultraviolet, and ultraviolet spectral ranges. Following absorption of light, photoreceptors interact with other signal transduction elements, which eventually leads to many molecular and morphological responses. While a complete signal transduction cascade is not known yet, molecular genetic studies using the model plant Arabidopsis have led to substantial progress in dissecting the signal transduction network. Important gains have been made in determining the function of the photoreceptors, the terminal response pathways, and the intervening signal transduction components.