si unit of power of a lens is
dioptre
title: Optical power text: Optical power Optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device: . High optical power corresponds to short focal length. The SI unit for optical power is the inverse metre (m), which is commonly called the dioptre. Converging lenses have positive optical power, while diverging lenses have negative power. When a lens is immersed in a refractive medium, its optical power and focal length change. title: Luminous intensity text: Luminous intensity In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit. Photometry deals with the measurement of visible light as perceived by human eyes. The human eye can only see light in the visible spectrum and has different sensitivities to light of different wavelengths within the spectrum. When adapted for bright conditions (photopic vision), the eye title: Steradian text: Steradian The steradian (symbol: sr) or square radian is the SI unit of solid angle. It is used in three-dimensional geometry, and is analogous to the radian, which quantifies planar angles. Whereas an angle in radians, projected onto a circle, gives a "length" on the circumference, a solid angle in steradians, projected onto a sphere, gives an "area" on the surface. The name is derived from the Greek στερεός "stereos" 'solid' + radian. The steradian, like the radian, is a dimensionless unit, the area subtended and the square of its distance from the center: both the numerator and denominator of title: Shear modulus text: Shear modulus In materials science, shear modulus or modulus of rigidity, denoted by "G", or sometimes "S" or "μ", is defined as the ratio of shear stress to the shear strain: where The derived SI unit of shear modulus is the pascal (Pa), although it is usually expressed in gigapascals (GPa) or in thousands of pounds per square inch (ksi). Its dimensional form is MLT, replacing "force" by "mass" times "acceleration". The shear modulus is one of several quantities for measuring the stiffness of materials. All of them arise in the generalized Hooke's law: The shear modulus is concerned with title: Lighting text: a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m). The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m. The amount of useful light emitted from a source or the luminous flux is measured in lumen (lm). The SI unit of illuminance and luminous emittance, being the luminous power per area, is measured in Lux. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes