There's no hard and fast rule about what headshot lighting must be. Headshot lighting is not determined by government agency, community standards, photography organizations, or anyone else. The lighting can be conceived by you and your photographer. Safe to say, a well-lit headshot should flatter the person, not make them look bad. Lighting method can be single source, open sky, studio flash, ambient light, softened with light boxes, hard edged light source, and multiple sources. Lighting style can be classy, moody, pensive, revealing, obscuring, avant garde, traditional, plain, classic Hollywood 1940's, and much more.