lysstrålens

lysstrålens is a central concept in optics describing the path along which light energy travels in a given direction. In geometric optics, a light ray is treated as a slender, idealized line or cone extending from a source and propagating through space or a medium. The concept is used to predict the paths that light follows when interacting with matter.

Through a homogeneous medium, lysstrålens proceeds in a straight line, at a speed v = c/n, where c is the vacuum speed of light and n is the refractive index of the medium. At interfaces between media, rays can be reflected or refracted. The law of reflection states that the angle of incidence equals the angle of reflection. Refraction follows Snell's law: n1 sin θ1 = n2 sin θ2, describing how the ray bends when entering a different medium.

Optical devices such as lenses and mirrors are analyzed by tracing lysstrålens to form images. Focusing, magnification, and aberrations are described in ray diagrams using focal lengths, principal axes, and angular relationships.

While the ray model is useful, it is an idealization. In wave optics, diffraction and interference show that light does not always travel along a single straight line, particularly near edges or at small scales compared with wavelength. Polarization concerns the orientation of the electric field and is a wave property, not captured by a single ray.

Historically, the geometric-ray approach traces to Fermat's principle of least time and was developed by Fermat, Descartes, Snell, and Huygens, forming the basis of geometric optics with widespread applications in imaging, spectroscopy, and fiber-optic communication.