The invention relates to a non-automotive-headlight lamp (1) comprising a lighting element (3) and a transparent bulb (2), which is at least partly equipped with an interference coating (4) for e.g. changing the color or color temperature of the lamp (1), and to a lighting unit (15) comprising such a lamp (1) being mounted in a reflector (12). But the invention is also related to lighting units (15) where the interference coating (4) is not applied to the lamp (1) but to the reflector (12). In these lamps (1) or lighting units (15) light components (8) not appropriately filtered by the interference coating (4) lead to undesired wavelengths in the illumination beam and/or to a compromised color uniformity of the beam. Such light components (8) may stem from missing or insufficient filters on part of the lamp (1), from non-normal incidence of the rays (8) on the filter (4), and, in reflectors (12) with interference coating (4), from direct light (8) not hitting the reflector (12). The invention adds a blocking device (5, 6, 7) to the lamp (1) or lighting unit (15) to substantially prevent these light components (8) to enter the illumination beam. Whereas constructively similar blocking devices (5, 6, 7) are known from automotive headlight lamps for preventing glare their benefits in the context of interference coatings (4) were overlooked in the prior art.