A solar tube, solar tunnel,[1]​ light tube, light duct or lumiduct[2]​ is a tubular duct that allows light to be transported from an illuminated area or lighting source to a dark area that is to be illuminated (for example, the interior of a building).

Tube lights are often used to improve lighting in areas with high demand for lighting intensity and quality (for example, in children's rooms, staircases, workplaces, and schools). Its main advantage is the ability to minimize the use of artificial lighting in the premises during the day.

A skylight refers to an opening above in the roof that allows daylight to pass through, while light tubes (often mistakenly called skylights) consist of:

Light tubes work on the principle of light reflection on a mirror or smooth surface, which makes it reach the interior. The light is natural, soft, providing a view of the space in true colors, without color changes due to lamps.

Tubes or light guides are manufactured in various configurations, for example, square section or circular section.

The inside of the tube can be either an aluminum reflective material (like a mirror), with a reflectance of approximately 96%, or a surface coating layer. At the bottom, a double glass diffuser (or diffusers) is installed, with thermal insulation properties, which disperses the light in the area to be illuminated (up to 25 m²).

A transparent dome is usually placed outside (on a side wall or on the roof), which can have a loss of up to 30% in intensity compared to a flat surface. The shape of the dome is normally hemispherical, so that at every moment of the day the light falls on a plane perpendicular to the dome. The domes are made of an acrylic material resistant to ultraviolet radiation.