Incandescent Lamp

Incandescent Lamp

A lamp is a device that produces light by using electricity to heat a filament or gas inside a glass or quartz bulb. Different sized and shaped lamps can be used for a broad range of tasks, such as general room illumination or accentuating a particular spot or object.

Lamp's are Mainly three type 

 1⇒ Incandescent 

i) Regular Filament

ii) Gas Filled

iii) Halogen

2⇒ Gaseous Discharge

👉 Sodium Vapour ↠ (a) High Pressure (HPSV or SON) (b) Low Pressure (LPSV or SOX)

👉Mercury Vapour

👉Neon

👉 Metal Halide 

👉 Fluorescent 

👉Compact Fluorescent Lamp (CFL)

3⇒.LED

Incandescent Lamp

Regular Filament: 

⇛  At high temperatures, both heat and light are generated.

⇛  The amount of light emission will increase with temperature.

 ⇛  Regular candles and fire are other instances of incandescent lamps.

⇛  Heat and, at higher temperatures, a little light are produced when an electric current is run       through a metallic cable.

⇛  Radiant Efficiency is the proportion of light output to total radiant energy.

⇛ Thomas Alva Edison, inventor of the first electric lamp .

⇛ The carbon filament was used in the first light.

⇛ Porcelain globe that has been fully emptied .

⇛ Filament, which is the fine filament inside the glass globe; 

⇛  Cement, which is the powder-filled cap.

Why was we evacuated?

Primarily to avoid the fine filament wire oxidising at high temperatures, which would cause metal oxide vapour to settle on the interior of the bulb and result in bulb blackening. Lamp life is also decreased.

Filament Material

Required Properties : 

(a) strong resistivity is . i.e. ρ

 (b) a high freezing point 

 (c) a low temperature coefficient of resistance, 

 (d) ductility, 

(e) enough mechanical power .

Tungsten is the most commonly used material for Filament

Why not Carbon ? 

Low m.p.  and  a -ve temperature coefficient of R that causes a significant current inrush

Why Tungsten ?

(a) High m.p. (3400 °C); 

(b) High m.p.

(c) low temperature R's coeff. (0.0051), 

(d) Vapour pressure is minimal 

(e) flexibility 

(f) strong mechanical resistance

Gas Filled Lamp

💥 In a standard filament (vacuum) lamp, the highest working temperature inside the bulb is 2000° C;        above this point, tungsten vapourizes quickly, blackening the lamp and shortening its life.

💥  More pressure and inert gas with a higher molecular weight should be used to combat this.

💥  A  mixture of argon and nitrogen (93:7).

💥  A temperature of 2300° C. and a radiation efficiency of  nearly 10%

💥 Nitrogen's function is to lessen the likelihood of arcing. 

💥  Krypton is the finest alternative, but it is impractical due to its higher cost.

Coiled Coil Structure of Filament

1. The presence of gas results in greater convection heat loss, which further lowers temperature         and radiant efficiency.

 2. A specially designed designed coiled coil filament can reduce convection heat loss.

 3. This design increases effective surface area.

Constructional Features

Constructional Features

Lamp Life and Lumen Depreciation 

✊ The cross sectional area of the filament diminishes due to the slow but constant evaporation of                 tungsten, increasing resistance.

✊ As a result, current current drops, along with Lumen output and efficiency. 

✊  Filament wire is also torn out as a result of ageing effect.

✊ Lamp intake is α V^1.55 and Lamp output is α V^3.55; as a result, Lamp Efficacy is α V^2.

✊ α V^-13 (Vacuum) or α V^-14 lamp life (gas filled)

✊  A compromise between lamp life and lumen power

Advantage and Disadvantage

Advantage:

Direct operation on standard distribution voltage (230V DC/1 φ, 50 Hz, AC) 

 Availability in different size and shape 

 Operating p.f. is unity (i.e. almost purely resistive load)

 No effect of surrounding air temperature

 Easy manufacturing technology

 Low cost 

 Good CRI ( 95 -100) 

 Restriking capability

 Dimming is possible

Disadvantage:

 Poor luminous efficacy (10-15 Lu/w) 

 Short life (500 – 1000 working hour)

Application

💢Was known as a GLS (General Lighting Service) lamp and was used for general lighting for a long          time. 

💢 Now CFL or LED have taken its position. 

💢Where colour reproduction is still crucial, it is utilised 

💢 Studios, photography, the textile or paint industries, a display of clothing or jewellery, or for                  decorative reasons, etc.