At least 90% of the area of each lot not devoted to off-street parking and/or occupied by buildings or other structures shall be kept in grass, shrubbery, trees or other natural cover. In addition, no use which requires the use of outdoor lighting or which is concentrated in time and space, such as but not limited to the use of a swimming pool or tennis court, nor shall the principal building be located within 100 feet of any abutting residentially zoned district.