LUMINANCE

SUHAIL TP MES Collage of Engineering

LED lighting

•Lighting in house should have good quality energy efficient lighting, such as LED.•LED(light emitting diode) replaces the jobs that low voltage has been used for.•The output and CRI( colour rendering index) of LED has improved sufficiently to allow like-for-like replacement.•LED has the advantage of being virtually maintenance free as well as cool to touch.

•Good quality LED spots will cost more than a traditional low voltage spot, but it requires little maintenance and running costs.•LED is a direct light source and does not have same ambient qualities as mains and low voltage.

LUMINOUS FLUX: Luminous flux is a quantitative expression of the brilliance of a source of visible light ,which is electromagnetic energy within the wavelength range of approximately 390nm to 770nm.

•This quantity is measured in terms of power emitted per unit solid angle from an isotropic radiators ,a theoretical point source that radiates equally in all directions in 3 dimensional space.•The standard unit of luminous flux is lumen(lm).• 1lm is equivalent to 1 candela steradian.

LUMINOUS INTENSITY: Luminous intensity is the quantity of visible light that is emitted in unit time per unit solid angle.•In photometry ,luminous intensity is a measure of the wavelength-weighted power emitted by light source in a particular direction per unit solid angle ,based on the luminosity function, a standardized model of sensitivity of human eye.•Unit of luminous intensity:

One lumen per steradian ,which is the unit of solid angle.•Unit of luminous intensity is also called standard candle or candela

LUMINANCE: Luminance is a photometric measure of luminous intensity per unit area of light travelling in a given direction.

•It describes the amount of light that passes through or is emitted from a particular area and falls within a given solid angle.•SI unit of luminance is candela per square metre ( ).

ILLUMINANCE: In photometry , Illuminance is the total luminous flux incident on a surface per unit area.

•It is a measure of how much the incident light illuminates the surface ,wavelength-weighted by the luminosity function to correlate with human brightness perception.•Luminous emittance is the luminous flux per unit area emitted from a source. It is also known as luminous exitance.