• Total Luminous Flux

 It is the measure of the total energy radiated from a light source in all directions, taking into account the varying sensitivity of the human eye to different wavelengths of light. SI Unit of luminous flux is lumen. It serves as the basis for calculating other parameters and can be used for comparing different light sources.

• Luminous intensity

 It is the measure of the luminous flux emanating from a point source within a solid angle of 1 steradian. The SI unit is Candela i.e. lumens per steradian.

• Luminous Efficacy

Lumen is the measure of luminous flux with respect to the energy consumed to produce it i.e. it is the ratio of luminous flux to power. The SI unit is lumens per watt. Luminous efficacy gives an understanding of the energy consumption by the LED to produce a certain level of illumination.

• Chromaticity Coordinates

Chromaticity is an objective specification of the quality of color emitted by a luminary source i.e. hue and saturation. Hue is the attribute of by which the light is discernible into its dominant wavelength or color. Saturation determined by a combination of light intensity and the distribution of the intensity across the spectrum of different wavelengths. As the human eye has 3 type of color sensors, the full plot of all visible colors is a 3 dimensional area with 3 tristimulus value: Luminance or brightness, hue and saturation. Chromaticity coordinates are determined by projecting the values in the tristimulus coordinate space into coordinates in chromaticity space through mathematical conversion.

• Correlated Color Temperature

A measure of the color of a light source relative to a black body at a particular temperature. It is based on the Kelvin Color Temperature Scale and is measured in degrees Kelvin (K). The figure below gives the range of color temperature for different color of the light source. Usually, incandescent lights have a low color temperature of approx. 2800K while white LED Lamps have a color temperature value between 2700-3500K. Color temperatures over 5000K are considered cool colors i.e. bluish white while lower temperatures around 2700-3000K are called warm colors i.e. yellowish white through red.