Spectroscopy Lab Report

Index

1. Introduction Spectroscopy is a term which refers to the interactions of various types of electromagnetic radiation with matter. It is also a study of the absorption and emission of light and other radiation by matter. Dependence of this process related to the wavelength of the radiation. Spectrometers are used to measure the properties of light over a specific portion of the electromagnetic spectrum.

Fig 1: Dispertion of the visiable light

2. Theory

Grating Spectrometer:

In a spectrometer if diffract light into specific wavelengths then uses grating. In this figure (2) we can see that light passes through the Input slit. When the

Here angles of red light are larger than blue light. Red light is the long wavelengths and Blue light is short wavelengths.(3)

Fig 2: Grating Spectrometer

Amplitude and Phase Grating:

In this fig we can see both Amplitude and Phase gratings. When an incident light pass through on the material can pass through the gaps on the substrate and transmit through it and remaining light reflects.

In phase grating light can pass through both the gaps and top of the substrate, so the reflected light has phase shift.

Fig

The ultraviolet and infrared wavelengths are invisible to human eye and the luminous intensity doesn’t count here. The watt of IR radiation is almost zero. Thus UV and IR LEDs don’t have lumen units.

Relationship between supply voltage of LEDs and emitted wavelength

The minimum voltage Vmin which required to cause photon emission, and we measure the wavelength of the emitted photons and use it to calculate the photon energy hf, we always find that eVmin < hf.

Some of the photon energy is supplied by thermal energy. In order to predict the wavelength of the photons emitted by a LED, we must take into account the distribution of charge carriers in the semiconductor material

Color temperature and connection with the wavelength:

Color temperature defines the color characteristics of light. It may be cool colors when the temperature over 5000k and it also warm color at lower color temperatures 2700 to 3000k. Color temperature is conventionally stated in the unit of absolute temperature, the kelvin, having the unit symbol K.