The U.S. government provides a number of free web-based resources for finding human factors information. I recently found the a searchable and browsable version of the Engineering Data Compendium: Human Perception and Performance - http://www.hsiiac.org/products/compendium.html
The Compendium is one of the standard references for Human Factors research - while much of the data is from studies 20+ years ago, these are universal psychophysical and perceptual analyses that remain relatively static. For example, searching for "visual angle" returned over a hundred results ranging from parameters for calculating visual angle, to recommended conditions for classroom viewing and visual acuity as a function of age.
This rich resource is a great starting place for determining what basic research has been done and identifying basic principles to apply in design.
FYI: The site is provided by the Human Systems Integration Information Analysis Center (Human Systems Integration IAC), a government owned, contract operated agency that deals with the interface between the human component of a system and its hardware and software using a total system approach.
