This Technical Memorandum provides a brief description of findings and references from a 1998 research project for measuring, determining, and identifying light trespass as a component of obtrusive light. Information is included about a specific experiment conducted as part of this research project, which was intended to provide input about how individuals (test subjects) react to light trespass. Subjects provided Objectionable Ratings (ORs) for three carefully selected test conditions. The Memorandum contains two main sections: (1) Research Project describing how the research was set up and conducted (essentially the goals/questions involved, information about the test subjects, three graphs summarizing the test data, and a discussion about how the test data was analyzed); and (2) Development of Recommendations defining area classifications, describing the impact of cufew laws on the light trespass problem, making quantitative recommendations about pre- and post-curfew light trespass levels, and developing guidelines on curfews for specific environmental zones. Exceptions are noted for special situations where the recommendations cannot be met. A list of 14 references used as a basis for the research program is also included. The main body of the research may be found through the Lighting Research Office of the Electric Power Research Institute (EPRI) in Palo Alto, California. the information in this Memorandum is useful for but not specific to roadway lighting. The results of the research presented here have provided input for two other IESNA publications, RP-33, Lighting for Outdoor Environments, and TM-10, Addressing Obtrusive Light (Urban Sky Glow and Light Trespass) in Conjuctions with Roadway Lighting. Since light trespass is a complicated topic, this Memorandum only begins to address the issues and is limited in its scope. Additional research is welcomed and needed.