Christmas rose in UV light. Coloured photograph of a Christmas rose (Helleborus niger) flower showing areas that reflect (pale areas) or absorb (dark areas) ultraviolet (UV) light. This flower has sepals (large outer petal-like structures) with high UV reflectance, and nectaria (modified petals, centre) and stamens (male sex organs, centre) with high UV absorption. This pattern, known as a 'nectar guide', is thought to attract pollinating insects, which can see in UV light. This image was taken on a digital camera adapted to filter and detect UV light. The resulting monochrome image was coloured on a computer. UV light is invisible to humans and does not have a true colour. See image B814/1644 for normal daylight version.