Introduction
In modern lighting design, the detailed explanation of the luminous intensity distribution curve of LED lamps is essential for understanding how LED luminaires perform in real-world environments.
The LIDC — short for Luminous Intensity Distribution Curve — is a graphical representation that shows how light is emitted from a luminaire in various directions. This curve directly influences visual comfort, illumination efficiency, and compliance with lighting standards.
For designers, engineers, and facility managers, understanding LIDC is not just a technical exercise; it is a tool for better lighting design, improved energy efficiency, and enhanced user comfort.
What is a Luminous Intensity Distribution Curve (LIDC)?
Definition
A Luminous Intensity Distribution Curve is a photometric diagram that displays how light intensity (in candela, cd) is distributed at different angles around a luminaire.
Why It Matters
- Defines the beam shape and spread of the LED lamp.
- Helps determine the suitability of a luminaire for specific applications.
- Ensures compliance with standards like IES and CIE.
Basic Elements in an LIDC
- Central point → Represents the LED lamp itself.
- Radial lines → Show the angle of light emission.
- Curves → Indicate light intensity at those angles.
How is an LIDC Measured?
Measurement Standards
- IES LM-79 (North America): Standard for testing solid-state lighting.
- CIE 121 (International): Defines photometric measurement principles.
Testing Process
- Conducted in a goniophotometer or an integrating sphere with goniometric add-ons.
- Light intensity is measured at increments (e.g., every 2.5°).
- Data is plotted in polar or Cartesian graphs.
Types of LIDC Graphs
1. Polar Diagram
- Circular graph.
- Common for visualizing beam spreads in spotlight and floodlight applications.
2. Cartesian Diagram
- Uses rectangular axes.
- Often used for roadway or asymmetric distribution.
3. 3D Distribution Models
- Advanced software creates 3D visuals.
- Shows light emission patterns in real space.
Key Features of LIDC in LED Lamps
- Beam Angle
- Defined as the angle between points where intensity falls to 50% of maximum.
- Narrow beam (≤30°) vs. wide beam (≥60°).
- Peak Intensity
- Highest luminous intensity, usually on-axis.
- Distribution Symmetry
- Symmetrical → same in all directions.
- Asymmetrical → directed to one side (e.g., street lighting).
- Light Spill & Cutoff
- Determines how much unwanted light spreads outside target zones.
Types of LIDC Patterns in LED Lighting
Symmetrical Distribution
- Uniform spread around the axis.
- Common in downlights and floodlights.
Asymmetrical Distribution
- Directs light in one direction.
- Essential for streetlights and wall washers.
Batwing Distribution
- Wide horizontal spread with less light directly below.
- Perfect for offices and retail environments.
Narrow Beam Distribution
- Concentrated light cone.
- Ideal for accent or spotlighting.
How to Interpret LIDC for LED Lamps
When reading an LIDC:
- Check peak candela values → How bright is the lamp at its center?
- Evaluate beam shape → Narrow, wide, or specialized?
- Look for uniformity → Will it cause dark spots or glare?
- Compare across models → Designers use LIDC to choose the right luminaire.
Applications of LIDC in Real-World LED Lighting
Residential
- Wide beam LIDC for living areas.
- Narrow beam for spotlighting artwork.
Commercial Offices
- Batwing distribution for uniform desk lighting.
- Reduces glare and eye strain.
Outdoor & Street Lighting
- Asymmetrical LIDC ensures roads are well lit.
- Minimizes light pollution in nearby buildings.
Industrial Facilities
- Symmetrical high-bay LIDC for large spaces.
- Improves visibility and worker safety.
Advantages of Using LIDC in LED Lamp Design
- Improved Efficiency – Reduces wasted light.
- Enhanced Comfort – Avoids glare and dark spots.
- Better Safety – Ensures consistent illumination.
- Design Precision – Matches luminaires to environments.
- Energy Savings – Optimizes placement and beam spread.
Challenges with LIDC in LED Lamps
- Complex Data – Graphs can be technical for non-engineers.
- Software Requirements – Advanced simulations needed.
- Variation in Standards – Regional testing protocols differ.
- Design Trade-offs – Narrow beams may create hotspots; wide beams may waste energy.
Tools for Working with LIDC
- Dialux – Free software for lighting simulations.
- Relux – Professional photometric planning tool.
- Autodesk Revit + IES Files – For BIM integration.
Best Practices for Designers Using LIDC
- Always review photometric files before selecting a luminaire.
- Simulate environments with LIDC data for accuracy.
- Balance aesthetics and performance — avoid fixtures that look good but have poor distribution.
- Match insulation class of drivers with LIDC needs — safe drivers plus optimized optics equal reliable luminaires.
Conclusion
The detailed explanation of the luminous intensity distribution curve of LED lamps reveals that LIDC is not just a graph — it’s a blueprint for how light behaves in real-world settings.
- It guides fixture selection.
- It ensures efficiency and safety.
- It enhances comfort and aesthetics.
By understanding and applying LIDC data, lighting professionals can deliver LED systems that are not only compliant and efficient but also optimized for human comfort and environmental sustainability.
