What Types of Light Sources Are Used in Machine Vision?
- Primary Light Source Types
A. LED (Light-Emitting Diode)
Dominance: Over 80% of modern machine vision systems use LED lighting due to its versatility and efficiency.
Advantages:
Spectral Range: Available in wavelengths from UV (365 nm) to IR (940 nm), with common visible-light options (red, blue, green, white).
Stability: Minimal thermal drift (±1% intensity fluctuation over 8 hours).
Lifetime: 50,000–100,000 hours of continuous operation.
Configurability: Structured lighting (e.g., dome, backlight, ring) for specific tasks like glare reduction or texture enhancement.
Applications: Surface inspection, OCR, semiconductor wafer alignment.
B. Halogen Lamps
Characteristics: Broad-spectrum light (400–2500 nm) with high intensity.
Limitations:
Short lifespan (~2,000 hours) due to filament degradation.
Significant heat output (up to 300°C), unsuitable for temperature-sensitive environments.
Use Cases: Legacy systems requiring full-spectrum illumination.
C. Xenon Strobes
Function: High-intensity pulsed light for freezing high-speed motion (e.g., 10 μs pulses at 100,000 lux).
Applications: Bottle/can inspection on fast-moving conveyors (>1,000 units/minute).
D. Laser Illumination
Precision: Coherent light for structured patterns (e.g., lines, grids) in 3D profilometry.
Wavelengths: Common options include 405 nm (blue), 635 nm (red), and 808 nm (IR).
Safety: Class 2/Class 3R lasers require compliance with IEC 60825 standards.
E. Specialized Sources
UV Lighting: 365 nm or 395 nm wavelengths for fluorescence detection (e.g., contaminant identification).
IR Illumination: 850 nm/940 nm for covert imaging or material penetration (e.g., pharmaceutical blister pack inspection). - Critical Selection Criteria
A. Spectral Matching
Align the light source’s wavelength with the target’s absorption/reflection properties.
Example: Blue (450 nm) light enhances contrast for orange PCB solder joint inspection.
B. Geometry & Uniformity
Backlights: >90% uniformity for silhouette-based measurements.
Dome Lights: Diffuse illumination to eliminate reflections on glossy surfaces.
C. Dynamic Control
Programmable LED arrays enable real-time adjustments:
Intensity modulation synchronized with camera exposure.
Multi-wavelength sequencing (e.g., red/green/blue for color analysis).
D. Environmental Durability
IP67/IP69K-rated housings for washdown environments.
EMI-shielded drivers for robotic integration. - Application-Specific Solutions
A. Automotive Manufacturing
Red Ring Lights: Detect scratches on dark car body surfaces.
Blue Coaxial Lights: Inspect transparent windshield coatings.
B. Electronics Inspection
UV Lighting: Reveal conformal coating defects on circuit boards.
High-Speed Strobe LEDS: Capture solder joint integrity at 200 FPS.
C. Food & Pharma
White Polarized Domes: Detect glass shards in transparent packaging.
IR Lighting: Verify pill fill levels through opaque blister foils. - Emerging Trends
Hyperspectral Imaging: Tunable LED arrays covering 400–1000 nm for material classification.
Smart Lighting: Integrated sensors for self-optimizing intensity/color based on ambient conditions.
Miniaturized Sources: Micro-LEDs (<5 mm²) for embedded vision in tight spaces.