Luminous flux differs from radiant flux (power) in such a way that the radiant flux is inclusive of all the emitted electromagnetic waves, while flux is weighed as a luminosity function of the sensitivity pertaining to various wavelengths visible to the human eye. Lumen is the SI unit of luminous flux, which refers to the rate at which the visible light is emitted from a source. If there is more than one wavelength, then one must integrate over the wavelength spectrum to achieve the total luminous intensity. The luminous intensity for light with wavelength λ is given as follows: But at other frequencies, a significantly more radiant intensity is required to reach the same luminous intensity, according to the human eye’s frequency response. The human eye is most sensitive near this specific frequency if adapted for bright conditions. The frequency chosen in the visible spectrum is corresponding to the wavelength of around 555 nm. The contribution of each wavelength is weighed by the standard luminosity function rather than adding up the contributions of each wavelength of light in the spectrum of the sources. Nonetheless, luminous intensity is comparable to radiant intensity. Candela is represented in terms of cd/m 2. It is the luminous power per unit solid angle emitted by a point light source in a specified direction. Candela is the SI unit of luminous intensity. The three main types of units of light are:Ĭandela It is useful in quantifying illumination (lighting) which is intended for human use. Photometry: It measures light with wavelength weighted for a standardized model of human brightness perception. Radiometry: It emphasizes the measurements of light power at all wavelengths. Light is measured with two sets of units which are given as follows: The frequency of light remains unchanged at all times when travelling from one medium to another. The speed of light in a vacuum is 3 X 10 8 m/s. Light has a specific frequency or wavelength spectrum. There are various levels of intensity to light. The primary properties of light are as follows: Learn more about Light and its properties Wavelength of 400-700 nm means a frequency range of around 430-750 terahertz (THz). Visible light has wavelengths that range from 400-700 nm (nanometers) or 4.00 x 10 -7 m to 7.00 x 10 -7 m, between the infrared waves that have longer wavelengths and the UV rays that have shorter wavelengths. 
Photons are the smallest quantity of energy that can be transported.Electromagnetic spectrum radiation is defined as a stream of photons – particles that have no mass travelling with wavelike properties at the speed of light.
Visible light is not very different from other parts of the electromagnetic spectrum except that they can be detected by the naked human eye.Electromagnetic radiations are the fluctuations of magnetic and electric fields that transport energy from one location to the other.Light or visible light refers to one of the parts of the electromagnetic spectrum that falls between radio waves and gamma radiation.
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