Light source

Pranav ram.RMech

What is light ??• Light is an electro magnetic radiation

that produces visual sensation.• The visible light has the wavelength

range of 4000 Ä to 8000Ä.• Light is nothing but the photons, having

energy E=hv

Source of light

1. Sun.2. High pressure mercury lamp.3. Low pressure mercury lamp.4. Medium pressure mercury lamp.5. Low pressure sodium lamp.6. High pressure sodium lamp.7. Laser.8. Light emitting diode.

Sun

• In the early experiments (and in everyday life), sunlight was used as a light source.

• Sun light consist of wide range of radiation and in the visible region, it comprises the violet, blue , green, yellow, orange and red components.

• According to early investigators observation when the photochemical sample is expose to sun light, after some period of time few changed.

High pressure Mercury lamp

High pressure mercury lamp

High pressure mercury lamp

• A  high mercury-vapor lamp  is a gas discharge lamp  that uses an  electric arc  through vaporized mercury to produce  light.

• This lamp operate in high ( 100 atm).

High pressure mercury lampDisadvantage :• It easily damage because it operate at very high

temperature so that quartz or glass envelope and nitrogen gas for cooling purpose is necessary.

• It has short life time due to high temperature and pressure.

• High pressure lamp are not commonly used in commercial photochemical apparatus.

low pressure mercury lamp

low pressure mercury lamp

Advantage

• It operate at very less temperature and low pressure.

• Low pressure mercury lamps are highly efficient in providing short wavelength ultraviolet energy.

The Low Pressure Sodium Lamp

The Low Pressure Sodium Lamp

• Low pressure sodium lamps only give monochromatic yellow light and so inhibit color vision at night.

• When the lamp is turned on it emits a dim red/pink light to warm the sodium metal and within a few minutes it turns into the common bright yellow as the sodium metal vaporizes.

Low pressure sodium lamp

Low Pressure Sodium Lamp

Advantage

• It have a lowpressure, low–intensity discharge source and a linear lamp shape.

High Pressure Sodium Lamp

High Pressure Sodium Lamp

• A sodium-vapor lamp is a gas-discharge lamp that uses  sodium in an excited state to produce light.

• The sodium D-line is the main source of light from the High-pressure sodium lamp.

• High-pressure sodium lamps are smaller and contain additional elements such as mercury.

• It produce a dark pink glow when first struck, and an intense pinkish orange light when sodium is warmed.

• Some bulbs also briefly produce a pure to bluish white light in between if the mercury achieves its high pressure arc discharge characteristic before the sodium is completely warmed.

LASERS

Laser

• Laser is a light source ,stands for Light Amplification by Stimulation Emission of Radiation.

• It produces light in a narrow frequency and to focus it in an extremely small area.

• Laser light is directional coherent and monochromatic.

Advantage Lasers are extensively used in various fields such as :DrillingCuttingWeldingMedical field

Light emitting diode • In photochemistry Light emitting diode is used as

a light source.

• A light-emitting diode is a semiconductor device that emits visible light when an electric current passes through it.

• The output from an light-emitting diode can range from red (at a wavelength of approximately 700 nanometers) to blue-violet (about 400 nanometers).

Blue LED

Light emitting diode

Advantage• It produces light at a single

wavelength, without the need for a monochromator.

• Lamp life is almost infinite and Light emitting diode sources are stable with little variation in bandwidth making them an attractive, low cost solution for simple applications.

Thank you

by Pranav ram