The strong effects of descriptive normative feedback (“how you compare to others”) on an individual’s electricity consumption have been documented in the IS literature. Here, we extend prior research on reference group effects (“whom to compare with”) by defining the relevance of the reference group in terms of similarity in contextual factors as opposed to personal characteristics. Specifically, we manipulate the spatial proximity of reference groups and test whether population density moderates the effects of feedback. In a field study with 560 energy customers, we find that reference groups that are close in terms of geographical proximity are more effective than more distant groups. However, population density does not moderate this effect. Designer of green information systems should therefore use reference groups that are close to the energy consumer with regard to geographical proximity, but they do not need to tailor the intervention to the energy consumer’s location.