Tristimulus Values and Chromaticity Coordinates

Tristimulus Values Fundamentally there are three colors. They are Red (R), Green (G) and Blue (B). Any color that stimulates human eyes is the mixture of R, G, and B in a certain proportion. Let us consider C is the color of an object as the test color. We have taken three sources of R, … Read more

Transmittance and Reflectance

Transmittance The radiant energy when it is measured in terms of monochromatic components, it becomes the function of the wavelength. So when this quantity comes into visual sensation then it becomes the term with the adjective spectral, like spectral radiance. But there are some ratioswhich are commonly used with same term but differ in the … Read more

Radiometric and Photometric Quantities

Radiometric Quantities Photometric Quantities Subscripts used in Illumination Engineering Notation S – Source Quantity D – Detector Quantity e – Energetic (Radiometric Quantity) v – Visual (Photometric) Quantities used in Illumination Engineering Notation dA – Infinitesimal area element Q – Energy (Luminous or radiant) Φ – Flux (Luminous or radiant) Ee – Irradiance Ev – … Read more

Colour Temperature of Black Body Radiation

What is Black Body? Black body is any inanimate body that always absorbs all radiation completely falling on it and radiates same amount of energy it receives at a constant temperature. There is no real existence of black body. But approximation leads the idea to a perfect black body in practice. As per this approximation, … Read more

Photometry and Radiometry

We are human beings living inside the zone of radiation. But we can not feel all the radiation with our eyes. Our eyes can detect only those radiation whose wavelengths are within range of 370 nm to 780 nm. This range is called visible range of wavelength. The radiation within this visible range of wavelength … Read more

Radiant Flux and Luminous Flux

The electromagnetic radiation with the wavelength from 100 nm and 1 mm is referred as the optical range of radiation. Inside this range, the electromagnetic radiation with wavelength 380 nm to 780 nm is called light and this range is the visible range of wavelength. The optical radiation with wavelengths shorter than 380 nm is … Read more

Irradiance and Illuminance

Irradiance is the radiant flux received by the detector area. The unit of irradiance is W/m2. Irradiance is denoted by Ee,λ, φs is the received radiant flux on the detector surface and AD is the detector area or surface. Irradiance always follows the Inverse Square Law. Suppose from a point source the radiant flux is … Read more

Radiant Exitance and Luminous Exitance

Radiant Exitance is defined as the radiant flux emitted from a source per unit area surface of that source. Radiant flux is the source quantity. It is denoted as Me,λ and its unit is W/m2. One important thing is that radiance is related to the source whereas the irradiance is related to the detector. Both … Read more

Radiance and Luminance

The radiant flux emitted from a point source in a certain direction per unit solid angle per unit projected area perpendicular to the specified direction is called radiance. Radiance is denoted by Le,λ and it is equal to the double derivative of radiant flux with respect to projected surface area As and Solid angle ωs. … Read more