steradian
Solid angle unit
A steradian is the unit of solid angle in three-dimensional space, analogous to how a radian measures angle in two dimensions.
One steradian equals the solid angle that, from the center of a sphere, subtends an area on the surface equal to the square of the radius.
A complete sphere encompasses 4π steradians.
The unit appears in physics and engineering when measuring light intensity, radiation, and other phenomena that spread outward from a point: The lamp emits 100 lumens per steradian.
Tapered solid, circular base
- apexUppermost point or culmination
- vertexPoint where edges converge
- subtendExtend opposite an angle
- field of viewExtent one sees simultaneously
viewing angle · hemisphere · octant · quadrant · projection · conical
Light output measure
- fluxContinuous change or flow
- intensityStrength or force level
- luminousEmitting or reflecting light
- candelaLuminous intensity unit
lux · illuminance · photometry · irradiance · isotropic · point source · inverse square law · emission
Unit of measurement
- SI unitStandardized measurement quantity
- dimensionlessWithout measurement units
- spatPetty verbal dispute
- unit conversionChanging measurement systems
Imaginary dome of stars
- field of viewExtent one sees simultaneously
- zenithPoint straight overhead
- stellarOf or like celestial bodies
- observatoryFacility for celestial study
cone
Tapered solid, circular base
field of view · viewing angle · hemisphere · octant · quadrant · projection · conical
lumen
Light output measure
candela · lux · illuminance · photometry · irradiance · isotropic · point source · inverse square law · emission · brightness
degree
Unit of measurement
- SI unitStandardized measurement quantity
- dimensionlessWithout measurement units
- spatPetty verbal dispute
celestial sphere
Imaginary dome of stars
- field of viewExtent one sees simultaneously
- zenithPoint straight overhead
- stellarOf or like celestial bodies