Fluorescent Lamp

 FLUORESCENT LAMP

An electric current is used to excite the gas molecules inside a lengthy, narrow glass tube coated with phosphorescent material to create a fluorescent lamp, also referred to as a fluorescent tube. The phosphorescent coating inside the tube emits visible light when the gas molecules are stimulated and release ultraviolet radiation as a result.

Contents:

 👉Construction

 👉Operation Principle

👉 Design Factors

 👉Connecting Diagram

👉 Optical Properties

 👉Application

Construction:-

⇛   It is a Low Pressure Mercury Vapour Gaseous Discharge Lamp in essence.

⇛  It consists of a glass tube with a configurable length and a typical diameter of 1.5" (T12), 1" (T8),         and 5/8" (T5) (0.38m to 1.52m)

⇛  It is equipped with two electrodes that are coated in emissive material for electrons (Oxide Coated         Tungsten Filament)

⇛  A very little amount of Argon is present in the tube at a pressure of 2.5 mm Hg, along with a few           drops of Mercury.

⇛  Fluorescent material, also called phosphor material, is placed on the inside of the tube.

⇛  It is connected to the starter, the power factor adjustment capacitor, and the ballast, also referred to as the choke (PFC)

Operation Principle:-

⋟ Electrodes are connected to a supply while switching (220 V)

⋟ High starting impulse voltage is provided by the starter and the choke (normally in the range of 1100      V)

⋟ When electrodes are heated, electrons are released.

⋟ They continue to collide with additional atoms, causing the gas to ionise as a result.

⋟ Under plasma state due to oscillations of electrons betweenground and upper energy levels, Electro Magnetic radiation takesplace continuously.

⋟ Ballast functions as a current limiter when in operation by generating a voltage drop that results in a lower voltage (almost 110 V) across the electrodes.

⋟ Capacitor can occasionally be used to increase pf.

Discharge of Mercury at Low Pressure:-

👉 Mercury's excitation level varies

👉Two resonance radiations at 253.7 nm and 185 nm are produced by electrical discharge in low               pressure mercury vapour, which normally converts most of its electrical discharge (63%) into UV-C       radiations.

👉3% of the energy is transformed into visible radiation, primarily at the wavelengths of 405 nm                (violet), 436 nm (blue), 546 nm (green), and 578 nm (green) (Yellow). The mixture's overall result          is a discharge of pale blue light, though obviously with very little effectiveness.

👉The remaining energy from the input is lost as heat radiations.

Fluorescence Principle :-

     Phosphor UV radiation is absorbed by a coating on the tube's interior wall. A portion of the energy        that is absorbed is reemitted as visible light. Fluorescence is the term for the phenomena. Heat is            emitted from the remainder.

  With a typical bulb, the overall UV to visible conversion efficiency is 40%. Hence, the total visible        energy is equal to 0.4*0.63+0.03 = 0.282, or almost 28%.

  .The colour output varies depending on the material (for instance, calcium tungstate produces blue,         zinc silicate produces green, and cadmium silicate produces yellow pink).

 Halo phosphorous or triphosphorous substance is used to produce white light. The latter has better          Lumen output and higher conversion efficiency, but it is more expensive.

Factors for Design

The efficiency of electrical energy's conversion to UV depends on:

⋟ Tube length or Discharge Arc Length (preferred shape is long tubular)

⋟  Inert Gas Used as Fill Gas (Argon, Krypton etc.)

⋟  Gas Fill Pressure

⋟ Mercury Vapour Pressure

⋟ Tube power loading (watts per square meter of discharge surface)

⋟ Tube Dimensions (Narrower the tube, more is the power loading and higher is the lamp voltage and        hence higher efficiency)

The efficiency of converting UV light to visible radiation varies on -

⋟ . The output of the lamp's emission spectrum

⋟  The quantum efficiency of the phosphor or phosphors employed. 

⋟  The phosphors or mixture of phosphors used.

Circuit Diagram

⋙ Choke (Ballast) is in series

⋙ Starter is in parallel with the lamp 

⋙ Initially Supply is applied across the starter 

⋙ Starter along with choke produces starting impulse - Hg Vapour ionised 

⋙ In running running Condition Condition starter starter becomes inactive

⋙ In running condition choke reduces voltage across lamp electrodes and thus limits the lamp current ⋙ Nowadays Electronic Ballast is used in place of Magnetic ballast due to its higher efficiency.

⋙The Control Gear Module will address choke and starter operation.

Fluorescent Lamp, Compact

#  Retrofit type is a good replacement for incandescent filament lamps since it fits in the same holder.       Integrated type has an electronic ballast built in, making retrofitting possible.

# The working process is similar to that of a low pressure mercury vapour fluorescent lamp. 

# . Non-Integrated - exterior magnetic or electronic ballast, retrofit is not possible.

# . Lumen o/p is proportional to the effective effective phosphor phosphor surface area. 

#  Typically in both cool and warm white and cool daylight range. 

#  CRI is good in the range of 80.

# . Luminous efficacy is in the range of 60 to 80 Lm/W.

# White LED has just taken the position of CFL.