**4. Radiation source**

In UV-VIS spectrophotometer, the normally pre-owned radiation is preferred to assets the hydrogen or deuterium lamps, the xenon discharge lamps, and mercury arcs. In all the assets, agitation is carried out by means of transient electrons through gasoline and those impacts in the midst of electron and gas molecules may bring about digital, vibrational, and rotational elation in the fume's particle [10].

The following are requirements of a radiation source:

1. It must be stable.


#### **4.1 Tungsten lamp**

The function is similar to an electric light bulb. It is a tungsten filament heated electrically to white heat. The structure is depicted in **Figure 3**.

#### *4.1.1 Disadvantage*

1.The intensity of radiation at a short wavelength < 350 nm is small.

2.To maintain a constant intensity, the electrical current to the lamp must be controlled.

*UV-Visible Spectroscopy for Colorimetric Applications DOI: http://dx.doi.org/10.5772/intechopen.101165*

**Figure 3.** *Tungsten lamp.*

#### *4.1.2 Advantage*

The lamps are generally stable, robust, and easy to use.

#### **5. Hydrogen discharge lamps**

Hydrogen gas is stored under relatively high pressure. When an electric discharge is passed through the lamp, excited hydrogen molecules will be produced which emit UV radiations. Hydrogen lamps cover the range of 3500–1200A°. These lamps are stable, robust, and widely used.

Hydrogen discharge lamp consists of hydrogen gas under relatively high pressure through which there is an electrical discharge. The hydrogen molecules are excited electrically and emit UV radiation. The high pressure brings many collisions between the hydrogen molecules, resulting in pressure broadening. This causes the hydrogen to emit a continuous broadband rather than a simple hydrogen line spectrum. It is stable, robust, and widely used. It is more expensive is the disadvantage.it is depicted in **Figure 4**.

#### **6. Deuterium lamp**

It is used in place of hydrogen, the intensity of radiation emitted is 3–5 times the intensity of a hydrogen lamp of comparable design. It is more expensive than a hydrogen lamp. But it is used when high intensity is required. It is represented in **Figure 5** [11].

#### **7. Xenon discharge lamp**

Xenon gas is stored under pressure in the range of 10–30 atmospheres. The xenon lamp possesses two tungsten electrodes separated by about 8 mm. When an

#### *Colorimetry*

**Figure 4.** *Hydrogen discharge lamp.*

**Figure 5.** *Deuterium lamp.* *UV-Visible Spectroscopy for Colorimetric Applications DOI: http://dx.doi.org/10.5772/intechopen.101165*

**Figure 6.** *Xenon discharge lamp.*

intense arc is formed between two tungsten ultraviolet light is produced. The structure is depicted in **Figure 6**.
