Luminance describes the amount of light emitted from or reflected by a surface, measured in candela per square meter. It relates to the light perceived by the human eye. Luminous flux is a measure of the total quantity of visible light emitted by a source across all directions, measured in lumens. Luminous intensity refers to the directional emission of visible light from a source per unit solid angle, measured in candelas. Illuminance describes the amount of light falling on a surface area and is measured in lux, relating to human perception of brightness, though brightness specifically refers to visual sensations rather than light measurements.

1. LUMINANCE
AND
ILLUMINANCE
HRISHI P.R.

2. LUMINANCE:
Luminance describes the measurement of the amount of light
emitting, passing through or reflected from a particular
surface from a solid angle
It also indicates how much luminous power can be perceived
by the human eye
The SI unit for luminance is candela/square meter (cd/m2).
Luminance is quantified using a spectroradiometer,
luminance meter or a chroma meter.

4. 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).
• 1 lm is equivalent to 1 candela steradian.

5. 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

7. ILLUMINANCE:
 Illuminance is a term that describes the measurement of the amount of light
falling onto (illuminating) and spreading over a given surface area.
• Illuminance also correlates with how humans perceive the brightness of an
illuminated area.
• As a result, most people use the terms illuminance and brightness
interchangeably which leads to confusion, as brightness can also be used to
describe luminance. To clarify the difference, illuminance refers to a specific kind
of light measurement, while brightness refers to the visual perceptions and
physiological sensations of light.
• The SI unit for illuminance is lux (lx).
• Illuminance (lux) is quantified using a chroma meter, an illuminance (lux) meter,
or an illuminance spectrophotometer.