brytningsstyrka

Brytningsstyrka, often translated as refractive power or dioptric power, is a measure of how strongly a lens or a curved optical surface converges or diverges light. It is inversely proportional to the focal length of the lens or optical system. The unit of brytningsstyrka is the diopter (D).

A lens with a brytningsstyrka of +1.00 D has a focal length of 1 meter. A lens with a brytningsstyrka of -1.00 D has a focal length of -1 meter, meaning it diverges light. Positive brytningsstyrka indicates a converging lens (like a magnifying glass), which brings parallel light rays together at a focal point. Negative brytningsstyrka indicates a diverging lens, which spreads parallel light rays out as if they originated from a focal point behind the lens.

The formula relating brytningsstyrka (P) to focal length (f) is P = 1/f, where 'f' must be in meters. For example, a lens with a focal length of 0.5 meters has a brytningsstyrka of 1/0.5 = +2.00 D. A lens with a focal length of -2 meters has a brytningsstyrka of 1/(-2) = -0.50 D.

In optometry and ophthalmology, brytningsstyrka is crucial for prescribing corrective lenses for vision problems like myopia (nearsightedness) and hyperopia (farsightedness). The power of the human eye's lens and cornea also contributes to its overall brytningsstyrka, which determines how well it can focus light onto the retina.