Topic is ultra violet radiation Give me its classification And high pressure mercury lamp production with diagram
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ultraviolet radiation classification UV-A UV-B UV-C wavelength ranges
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https://lamptech.co.uk/Documents/M1%20Introduction.htm
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A detailed labeled cross-section diagram of a high pressure mercury vapor lamp showing: outer glass bulb (elliptical envelope), inner quartz arc tube, two main tungsten electrodes at each end of the arc tube, one auxiliary starting electrode near one main electrode connected via a resistor, mercury droplets inside arc tube, argon buffer gas filling, nitrogen-filled outer envelope, molybdenum foil seals at the ends of the arc tube, support frame/mount wires, and lamp base. Include arrows showing UV light emission from the arc tube. Clean scientific diagram on white background with clear labels and annotations.
Here is a complete, organized answer on both topics:
Ultraviolet (UV) Radiation
1. Classification of UV Radiation
UV radiation occupies the electromagnetic spectrum between visible light and X-rays, with a wavelength range of 100-400 nm. It is divided into three primary bands (WHO / CIE standard):
| Band | Wavelength | Also Called | Atmospheric Fate |
|---|---|---|---|
| UVA | 315 - 400 nm | Long-wave UV / "Black light" | NOT absorbed by ozone; ~90% reaches Earth's surface |
| UVB | 280 - 315 nm | Medium-wave UV | Mostly absorbed by ozone; ~10% reaches surface |
| UVC | 100 - 280 nm | Short-wave UV / Germicidal UV | Completely absorbed by ozone and atmosphere |
Further Sub-divisions
UVA is further split into:
- UVA-I: 340-400 nm (less biologically damaging, used in phototherapy)
- UVA-II: 315-340 nm (more energetic, contributes to erythema)
UVC includes:
- Far UV (FUV): 200-280 nm
- Vacuum UV (VUV): 100-200 nm (absorbed by air itself; only propagates in a vacuum)
Key Properties by Band
UVA (315-400 nm)
- Penetrates deep into the dermis
- Causes photoaging, indirect DNA damage via reactive oxygen species (ROS)
- Primary driver of tanning; used in PUVA phototherapy
- Source of ~90% of total UV reaching Earth's surface
UVB (280-315 nm)
- Absorbed mainly in the epidermis
- Causes direct DNA damage - characteristic C→T and CC→TT dipyrimidine mutations (UV signature mutations)
- Responsible for sunburn, vitamin D synthesis, and skin cancer induction
- Most carcinogenic band in terms of direct DNA mutagenesis
UVC (100-280 nm)
- Most energetic and most damaging type
- Completely filtered by the atmosphere - does NOT naturally reach Earth's surface
- Artificially produced by germicidal lamps (peak emission 254 nm)
- Disrupts DNA and microbial cell walls - used for disinfection
Sources: WHO UV Q&A | CDC UV Facts | EU Scientific Committee Glossary | Fitzpatrick's Dermatology, Vol. 1
2. High-Pressure Mercury Lamp - UV Production
What It Is
A high-pressure mercury (vapour) lamp is a gas-discharge arc lamp that generates UV and visible radiation by passing an electric arc through vaporised mercury at high pressure (typically 2-18 bar at operating temperature). It was the first metal vapour lamp mass-produced for general use and remains important as an artificial UV source.
Construction
Key Components:
| Component | Material | Function |
|---|---|---|
| Arc tube (inner) | Fused quartz | Contains the discharge; quartz transmits UV (200-400 nm) |
| Main electrodes (x2) | Tungsten | One at each end of arc tube; sustain the main discharge |
| Auxiliary starting electrode | Tungsten | Placed beside one main electrode, connected via 10-30 kΩ resistor |
| Mercury | Elemental Hg | A few mg; primary radiation source when vaporised |
| Buffer gas | Argon (25-50 torr) | Carries discharge while mercury warms up |
| Outer envelope (bulb) | Hard glass / quartz | Protects arc tube; may carry phosphor coating |
| Outer gas fill | Nitrogen or Ar-N₂ | Prevents oxidation of seals; slows phosphor degradation |
| Seals | Molybdenum foil | Hermetic seal between quartz tube and metal leads |
Working Principle - Step by Step
Stage 1: Ignition (Cold Start)
- Full open-circuit voltage is applied across the arc tube
- The main electrode gap is too large for direct ionisation
- Voltage is also applied between the main electrode and the auxiliary electrode (small gap) via a resistor
- The small gap ionises the argon gas - a small discharge strikes
- Free electrons, ions and photons flood the arc tube
Stage 2: Warm-up (2-5 minutes)
- The small argon discharge generates heat
- Heat vaporises mercury droplets into mercury vapour
- The discharge transitions from argon to mercury vapour
- Lamp colour shifts from dark blue (low-pressure Hg lines) to blue-green/white
- Pressure builds progressively inside the arc tube
Stage 3: Full Operation
- Mercury is fully vaporised; pressure reaches 2-18 bar depending on lamp power
- High-pressure arc emits a broad UV spectrum
- The high pressure causes spectral line broadening (pressure broadening)
- Characteristic emission lines: 254 nm (UVC), 313 nm, 365 nm (UVA), 404 nm, 436 nm, plus visible green/yellow/violet lines
- The strongest UV irradiance is typically around 365 nm
Stage 4: UV Emission Mechanism
- Electric current accelerates electrons between electrodes
- Electrons collide with mercury atoms, exciting them to higher energy states
- Mercury atoms return to ground state, releasing energy as photons
- Photon wavelength = inversely proportional to the energy difference between states
- Quartz tube transmits UV wavelengths that glass would block
Emission Spectrum of High-Pressure Mercury Lamp
| Wavelength | Region | Intensity |
|---|---|---|
| 254 nm | UVC | Present (stronger in low-pressure) |
| 313 nm | UVB | Moderate |
| 365 nm | UVA-I | Strongest UV line |
| 404-436 nm | Violet (visible) | Strong |
| 546-578 nm | Green/Yellow | Strong |
Phosphor Coating (Fluorescent Versions)
The inner surface of the outer bulb is coated with a fluorescent phosphor that:
- Absorbs the invisible UV (especially 365 nm)
- Re-emits it as visible red/white light
- Improves colour rendering by filling in the lamp's red deficiency
Applications
- UV phototherapy (PUVA, UVB narrowband therapy for psoriasis, vitiligo)
- UV curing (adhesives, printing inks, coatings)
- Germicidal/disinfection (especially medium-pressure variants)
- Molecular spectroscopy
- Street/industrial lighting (with phosphor coating)
- Forensic and fluorescence examination
Summary: UV radiation spans 100-400 nm and is classified as UVC (100-280 nm, most energetic, germicidal), UVB (280-315 nm, sunburn/DNA mutagenesis), and UVA (315-400 nm, long-wave, photoaging). The high-pressure mercury lamp produces UV by ionising mercury vapour with an electric arc inside a sealed quartz tube - ignition is assisted by an auxiliary electrode, and full UV output is reached only after a 2-5 minute warm-up as mercury fully vaporises and pressure builds to 2-18 bar.
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