Ultraviolet not necessarily coincide; for example one applied physics publication used a boundary of 190 nm between hard and soft UV regions. Very hot objects emit UV radiation (see black-body radiation). The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot stars emit proportionally more UV radiation than the Sun. Sunlight in space at the top of Earth's atmosphere (see solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m in vacuum. However, at ground
Ultraviolet communication in butterflies to reflect ultraviolet light. In effect, females are removing the ultraviolet signal that initiates male sexual behavior, resulting in the abrupt halt of male sexual behavior. Female White Cabbage Butterflies take advantage of the personal butterfly ultraviolet communication system to also reject males by removing an ultraviolet reflectance signal. Some butterfly species use ultraviolet light as a method of signaling their sex. For example, in the species "Eurema lisa", males possess the structural requirements necessary to reflect ultraviolet light discussed previously, but females lack the ultraviolet light reflecting ridges. In both sexes of this species, a flutter response, or the