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 the pterins absorb the ultraviolet light. Thus, butterflies are able to reflect ultraviolet light as a result of the organization and composition of their wing scales resulting in thin layer constructive interference and can absorb ultraviolet through the action of pterin pigments. Butterflies receive ultraviolet signals by utilizing a special photoreceptor pigment in the butterfly eye. The butterfly eye is similar to the average insect eye in that it is composed of numerous ommatidia. Each butterfly ommatidium contains nine photoreceptors with generally each photoreceptor utilizing a single visual pigment. A UV sensitive visual pigment is responsible for a butterfly’s ability