An illumination system comprising at least one luminaire, the luminaire comprises: - at least one light-emitting semiconductor chip having a main emission side, and - a reflector having a reflection side facing the main emission side, the reflection side is a freeform different from a circle and ellipse and parabola and hyperbola when seen in cross-section, wherein - the luminaire is arranged on a wall or a pillar of a building which has at least in part a glass front, - the luminaire is arranged to illuminate a part of the building that protrudes from the wall or pillar, - at most 2% of the light emitted by the luminaire enters the building so that glaring within the building is avoided, - a base line runs through the main emission side and a local height (h) of the reflection side is measured against the base line, - a local focal length (f) of the reflection side increases along the local height (h), concerning ray bundles coming in parallel with the base line from an exterior of the luminaire, - there is no common focal point for all of the local heights (h), - the reflection side, when seen in cross-section, has the shape of a modified parabola, so that a distance of focal points of the ray bundles toward the reflection side along the base line increases with increasing local height (h), - the base line is in parallel with a mounting plane of the luminaire, the luminaire is mounted on the building with the mounting plane so that the mounting plane is on a side of the luminaire facing the building, - an angle between the base line and a direction of maximum emission of the luminaire is at least 2° and at most 15°, the direction of maximum emission points away from the mounting plane, and - the base line runs through the main emission side so that the base line and the main emission side have a point of intersection. - at least one light-emitting semiconductor chip having a main emission side, and - a reflector having a reflection side facing the main emission side, the reflection side is a freeform different from a circle and ellipse and parabola and hyperbola when seen in cross-section, - the luminaire is arranged on a wall or a pillar of a building which has at least in part a glass front, - the luminaire is arranged to illuminate a part of the building that protrudes from the wall or pillar, - at most 2% of the light emitted by the luminaire enters the building so that glaring within the building is avoided, - a base line runs through the main emission side and a local height (h) of the reflection side is measured against the base line, - a local focal length (f) of the reflection side increases along the local height (h), concerning ray bundles coming in parallel with the base line from an exterior of the luminaire, - there is no common focal point for all of the local heights (h), - the reflection side, when seen in cross-section, has the shape of a modified parabola, so that a distance of focal points of the ray bundles toward the reflection side along the base line increases with increasing local height (h), - the base line is in parallel with a mounting plane of the luminaire, the luminaire is mounted on the building with the mounting plane so that the mounting plane is on a side of the luminaire facing the building, - an angle between the base line and a direction of maximum emission of the luminaire is at least 2° and at most 15°, the direction of maximum emission points away from the mounting plane, and - the base line runs through the main emission side so that the base line and the main emission side have a point of intersection.