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Colorimetry

Colour

👉Variety is a quality not entirely settled by the light's unearthly structure and the communication with the natural eye. Subsequently, variety is a psychophysical

peculiarity, and impression of variety is emotional.

👉The cone cells are gathered into three kinds, each answers a piece of the

range, with top reactions comparing to blue, green, and red light. The

cooperation of these gatherings is then answerable for the boost which is deciphered by the mind as variety.

👉At the point when a variety is made freely like by a light, is called source

variety.

👉For object tone, it is important to decide and assess the ghastly dissemination of the illuminant. This is on the grounds that the variety shows up distinctively when the

light source changes.

Colorimetry

🧿 Colorimetry, the study of variety estimation, is generally utilized in commerce, industry and the lab to communicate variety in mathematical terms andto measure variety contrasts between examples. Applications incorporate paints, inks, plastics, materials and attire, food and drinks, drugs and cosmetics, shows, and different parts and items that reflect or communicate variety.

🧿 The resultant variety impact of blending three shaded lights, red, green, and blue. The red, green, and blue can be known as the primaries and the subsequent yellow, cyan, and fuchsia the secondaries. Source Tone is of addititive blending nature. • The shade of a still up in the air by colors. These are synthetics which make a given tone by deducting (retaining) portions of the range of the occurrence light. The leftover light is reflected and this gives the item its variety trademark. Object tone is of subtractive nature.

🧿The properties of variety which are intrinsically discernable by the natural eye are shade, immersion and splendor. • It is found that a wide range of mixes of light frequencies can create a similar view of variety. This can be placed in context with the CIE chromaticity graph.

CIE chromaticity diagram

Colorimetric instrument

💢 A tristimulus colorimeter gauges the tristimulus upsides of a variety.

💢 irrefutably the ghastly power conveyance of a light source can be estimated with

a spectroradiometer.

💢 Reflected variety can be estimated utilizing a spectrophotometer.

💢 A spectrocolorimeter is a spectrophotometer that can is a spectrophotometer that can work out compute tristimulus values.

Colour rendering index (CRI)

💥A variety delivering record (CRI) is a quantitative proportion of the capacity of a light source to reveal the shade of different items steadfastly in correlation with an ideal or normal light source (typically we consider as sunshine.). Light sources with a high CRI are alluring in color-basic applications like activity theater and workmanship reclamation.

💥It is characterized by the Worldwide Commission of Enlightenment (CIE) as follows:

Variety delivering: Impact of an illuminant on the variety appearance of items by cognizant or subconscious subliminal correlation examination with their variety appearance under a reference illuminant.

💥The variety delivering record (CRI) is estimated as a number with greatest worth 100. The minimum worth might be even negative ( if there should be an occurrence of LPSV light). Under light of low CRI lamp, all objects seem to be same in variety (blackish Grey).A CRI of 100 shows the real nature of the object. Brilliant and incandescent lamp sources have a CRI of 100 or almost 100.

💥Related variety temperature of a light source (CCT) : It is the outright temperature of a blackbody whose chromaticity most almost looks like that of the light source. If chromaticity precisely coordinates with any worth on the dark body radiator, then, at that point, it is named as Colour Temperature (CT). In reality CCT is the general term used to depict variety character of any light source.

Metal Halide Lamp

A specific type of high-intensity discharge (HID) lamp known as a metal halide lamp produces light by using a combination of metal halide salts.

The metal halide salts and other gases are contained in a tube that the lamp employs to generate light by circulating an electric current through it.

Metal Halide Lamp: Working Principle

💥A metal halide lamp can be considered as an extension of HPMV lamp.

💥In HPMV lamp visible radiations are at 3 spectral areas ; Blue (436nm), Green(546nm) & Yellow(578nm). Red region is absent. It causes poor colour renditionproperty and moderate luminous efficacy.

💥By adding suitable suitable metals with lower excitation excitation potentials potentials to the arc tube, thecolour property i.e. CRI can be improved.

💥Metals may be of different types – Single Line radiators ( Sodium – Yellow, Indium – Blue), Multi Line Radiators (rare earth maetals like Scandium, Thorium, etc), Molecular Radiators for wide band light emissions.

💥 But they are generally highly reactive and would damage the quartz arc tube.

💥By adding the metals in the form of halides these problems can be eliminatedto a satisfactorily good extent.

💥Iodides (less reactive) are mostly used & Fluorides never used (Strong reactive)

Working Process

≽ At first the output spectrum is only due to Hg Vapour, because Halides remainsolidified.

≽ On further heating Halides dissociate in the hot central regionof thedischarge tube allowing their metal atoms to make a contribution to the lightoutput by their characteristic spectral emission mostly in the Red region.

≽ In the relatively cool region near arc tube wall, metal and halogen atomsrecombine to form the halides again. These halides are much less chemicallyreactive than the metal ions and hence cause less damage to the fused silica(quartz) glass of arc tube.

≽ This cyclic process results efficient lamp operation with better CRI.

≽ The radiation Characteristics of MH lamps are strongly dependent of thevapour pressure of the halides and hence the Cold and Hot spot temperaturesof the arc tube

Optical Characteristics and Applications

👉 MH lamps can be made in various size and rating and with different colour output – from Daylight to even UV.

👉 With varying composition of Metal Halides and inside pressure, MH lamps are available with variable optical properties -

👉 Luminous Efficacy – 70 -100 Lm/W

👉 CRI – 70 -90  CCT – 3600 K – 5600 K

👉 Life – 6000 – 15000 working hours

👉 Application – Quality Interiors, Wide Area Floodlighting, Stage and Studio Light, Sports Light particularly for Colour TV Broadcasting.

Ceramic Discharge Metal Halide lamp (CDMH)

🧿Major criticism to the MH lamp is - poor lamp to lamp colourconsistency (less uniformity) and changes in colour through out the life(lack of stability)

🧿Ceramic Discharge Lamp is recent development to solve the issue to asatisfactory extent.

🧿Ceramic Ceramic can withstand withstand higher temperatures temperatures than quartz glass. Thispermits higher wall temperatures thereby evaporating more of themetal halide salts into the gas arc and allowing for more efficient use ofthe chemicals. Ceramic lamps offer improved luminous efficacy andcolour rendering as a result.

🧿Normally Poly Crystalline Alumina (PCA) is used.

🧿However, in contrast to silicon, aluminum hardly dissolves in tungstenand the reaction with rare earth elements are much more self limiting.

🧿But there is a colour shifting in output from Quartz to Ceramic Tube

Mercury Vapour

Mercury Vapour

A mercury vapour lamp is a particular kind of high-intensity discharge (HID) lamp that emits illumination using mercury vapour.
When an electric current is run through a tube holding mercury vapour and other gases, the mercury atoms become excited and emit ultraviolet light.
This is how the lamp operates.The lamp's interior phosphorescent coating is then activated by the ultraviolet light, which causes it to produce visible light.

Low Pressure Mercury Discharge

💢Mercury Has Different excitation level

💢Electrical discharge in Low Pressure Mercury Vapour is mostly(typically 63%) converted into

UV-C radiations -Two resonanceradiations radiations are at 253.7 nm & 185 nm

💢Approximately 3% is converted into visible radiations –predominantly at 405 nm (Violet), 436 nm (Blue), 546 nm(Green) & 578 nm(Yellow). The overall effect of the mixture isa discharge of Pale Blue colour light, but obviously with verysmall efficacy.

💢The remaining Input energy is dissipated as heat radiations.

Low Pressure Mercury Vapour UV Lamp

High Altitude The most common application of mercury discharge is in fluorescent lamps, which produce visible radiation using the fluorescence principle.

To convert UV radiation into visible light, the lamp's interior wall is coated with phosphor.

💥Fluorescent Lamp will be discussed in details in the next module.

💥But Low Pressure Pressure Mercury Mercury Vapour Lamp without without any phosphorphosphorcoating producing UV Rays, are also used in some specific fields.

UV Lamp Application

⋙ UV lamp finds its application as germicidal or Ozone absorption lamps. UVis also essential for Chromatography, Photochemistry, Calibration of UVDetectors, Calibrations of Spectrophotometer, and more.

⋙ UV-C light is germicidal – it deactivates the DNA of bacteria, and otherpathogens and thus destroys their ability to multiply and cause disease. UV-C germicidal lamp has its application in medical sector (pharmaceutical production, laboratories, hospitals and clinics) Water purification, Industryand Food Processing

⋙UV also attracts insects and flies. So UV lamps are also used in electricinsect killer. A light source (emitting UV and blue visible radiations) attractsinsects to an electrical grid, where they get fatal electric shock by touchingtwo wires with a high voltage between them. It is housed in a protectivecage to prevent human and larger animals to touch the high voltage grid.

High Pressure Mercury Vapour Lamp :

Construction

⋟ Normally operated vertically.

⋟ Inner Arc Tube - hard glass i.e quartz in order to withstand high temperature

⋟ It consists of Tungsten electrodes, Mercury and small amount argon gas.

⋟ Outer glass (Elliptical shape) - Soda-Lime silicate silicate glass and for higher rating Borosilicate glass.

⋟ Space between inner & outer glass tube - completely or partially evacuated to reduce convection heat loss.

⋟ For cold start an auxiliary electrode - molybdenum or tungsten positioned close to one of the main electrode, but connected to the opposite supply polarity through a limiting carbon resistor of 10-30 KΩ

HPMV Lamp : Working Principle

⇛ Argon (Filling gas) pressure – 2500-5000Pa, Mercury dose 18 to 36 mgdepending on the lamp rating.

⇛Initially supply is in between main and auxiliary electrode resulting dischargethrough argon – reddish radiation.

⇛ After some time Hg is vaporised, ionisation and discharge of Hg starts.

⇛After complete vaporisation of Hg, a low resistance path is created betweentwo main electrodes electrodes and the arc is shifted shifted to main electrodes electrodes.

⇛ Auxiliary electrode along with the limiting resistance becomes inactive.

⇛ When fully run up the lamp operates at 1 to 2 Atmosphere. For higher pressurefurther spectrum broadening is achieved generating more white light .

⇛ Due to increased pressure comparatively broad spectrum is developed andhence bluish white radiation together with UV, but it is deficient at Red end ofthe spectrum.

⇛ The phosphor coating on the inner wall of the outer envelop increases thelamp efficacy by converting UV into Red Light (600-750nm). Colour renderingproperty is also improved.

HPMV Lamp: Electrical & Optical Characteristics and Application

🧿Operating Voltage – Supply Voltage

🧿Operating Temperature – 600˚C

🧿Power rating – 80 – 1000 W

🧿Takes 4-5 min for full brilliance

🧿Colour – Bluish White

🧿Life – 10000-24000 working hours

🧿CRI (Typical (Typical 250 W) – 16-20 (Clear Bulb) & 40- 50 (Phosphor Coated)

🧿CCT (Typical 250 W) – 6000 K (Clear Bulb) & 3800 K (Phosphor Coated)

🧿Luminous efficacy – 35-65 Lm/W

🧿Application – High ceiling manufacturing bay, Railway Yard, Airport, Shopping Centre, Stage, Sports Lighting etc.

🧿After damage of lamp, disposal of mercury is another problem - health hazardous

🧿Now a days almost obsolete due to poor efficacy and CRI.

Halogen Lamp & Gaseous Discharge Lamps

Halogen Lamp

👉 Small-scale halogen (preferably iodine) vapour addition to the pressing gas

👉It uses a chemical process known as the regenerative cycle to restore some of the evaporated tungsten vapour to the filament.

👉Tungsten + Iodine = Tungsten Iodide

👉Thermal breakdown of Tungsten Iodide near the filament at higher temperature results in deposition of tungsten on filament

Advantage and Application

Advantages:

💢Higher operating temp. &hence better Luminous efficacy (22- 33 Lu/W)

💢 Longer life (2000 working hours)

💢Reduced blackening of lamp

💢Reduced dimension

💢 Better colour rendering

Application:

💥Outdoor Illumination of building, playground, gardens, airport runways etc.

💥Indoor illumination of public halls, factories, sports halls, TV studio etc.

Gaseous Discharge Lamps

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

👉Mercury Vapour

👉Neon

👉 Metal Halide

👉 Fluorescent

👉Compact Fluorescent Lamp (CFL)

Sodium Vapour Lamp

A sodium vapour lamp is a particular kind of high-intensity discharge (HID) lamp that emits illumination using sodium vapour.
The lamp works by passing an electric current through a tube containing sodium and other gases, which causes the sodium atoms to become excited and emit yellow light.

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.

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.

DEFINITIONS OF TERMS USED IN ILLUMINATION

LIGHT:

⇛ Light is a type of brilliant energy that movements in waves comprised of vibrating electric and attractive fields. These waves have both a recurrence and a length, the upsides of which separate light

from different types of energy on the Electromagnetic Range or Ether Range. Fig.1 shows the

ether range.

The Enlightening Designing Society characterizes light as "brilliant energy that is equipped for energizing

the retina and creating a visual sensation." Light, consequently, can't be independently portrayed in

terms of brilliant energy or of visual sensation yet is a mix of the two.

Light might be considered little heaps of waves Light might be considered little heaps of

waves produced in discrete parcels called photons.

Apparent LIGHT OR Noticeable Emanation:

Noticeable light is the electromagnetic radiation of a frequency to which eyes are delicate as can

be seen on the electromagnetic range, addresses a tight band between bright light

(UV) and infrared energy (heat). It is the radiation described by frequencies of around 0.38

µm to 0.78 µm. These light waves are fit for energizing the eye's retina, which results in a

visual sensation called sight.

Fig 2 :- Visible Light Spectrum & Sensitivity

LUMINOUS FLUX (Φ):

The total quantity of light emitted per second by a light source is known as the Luminous Flux i.e. it is the time rate of flow of light. It is measured in lumen (lm).

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Colorimetry

Colour

Colorimetry

CIE chromaticity diagram

Colorimetric instrument

Colour rendering index (CRI)

Metal Halide Lamp

Contents:

Metal Halide Lamp: Working Principle

Working Process

Optical Characteristics and Applications

Ceramic Discharge Metal Halide lamp (CDMH)

Mercury Vapour

Contents:

Low Pressure Mercury Discharge

Low Pressure Mercury Vapour UV Lamp

UV Lamp Application

High Pressure Mercury Vapour Lamp :

Construction

HPMV Lamp : Working Principle

HPMV Lamp: Electrical & Optical Characteristics and Application

Halogen Lamp

Advantage and Application

Advantages:

Application:

Gaseous Discharge Lamps

Sodium Vapour Lamp

A sodium vapour lamp is a particular kind of high-intensity discharge (HID) lamp that emits illumination using sodium vapour.The lamp works by passing an electric current through a tube containing sodium and other gases, which causes the sodium atoms to become excited and emit yellow light.

Contents:

(a) High Pressure (HPSV or SON)

Construction:-

Building Method

Applications and Visual Properties

(b) Low Pressure (LPSV or SOX)

Construction

Working Process

Optical Characteristics and Application

Incandescent Lamp

Lamp's are Mainly three type

1⇒ Incandescent

2⇒ Gaseous Discharge

Incandescent Lamp

Regular Filament:

Why was we evacuated?

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 .

Why not Carbon ?

Why Tungsten ?

Gas Filled Lamp

Coiled Coil Structure of Filament

Constructional Features

Constructional Features

Lamp Life and Lumen Depreciation

Advantage and Disadvantage

Application

FLUORESCENT LAMP

Contents:

Construction:-

Operation Principle:-

Discharge of Mercury at Low Pressure:-

Fluorescence Principle :-

Factors for Design

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

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

Circuit Diagram

A sodium vapour lamp is a particular kind of high-intensity discharge (HID) lamp that emits illumination using sodium vapour.
The lamp works by passing an electric current through a tube containing sodium and other gases, which causes the sodium atoms to become excited and emit yellow light.