When designing outdoor lighting, it’s crucial to go beyond simply selecting fixtures based on brightness or budget. Properly assessing the space and understanding the light distribution patterns are key to creating an effective and efficient lighting scheme. This article will explore light distribution patterns, the relationship between light distribution and horizontal angles, and how to utilize this information for optimal lighting.

Types of Light Distribution

Light distribution refers to how light is spread from the fixture and is categorized by the Illuminating Engineering Society of North America (IESNA) into five main types. Understanding these types helps in selecting the right fixtures for various applications.

1. Type I Light Distribution

• Description: Provides a narrow, symmetrical light beam, ideal for use in the middle of walkways or narrow paths.
• Horizontal Angle: The width of the light pattern is approximately equal to the fixture’s height. For example, a fixture mounted at 10 meters high will cast light approximately 10 meters wide.

2. Type II Light Distribution

• Description: Offers a slightly wider light distribution, suitable for fixtures placed at the edge of wide paths, alleys, or roadways.
• Horizontal Angle: Light spreads up to 1.5 times the height of the fixture. A 10-meter high fixture will cast light about 15 meters wide.

2. Type II Light Distribution

• Description: Offers a slightly wider light distribution, suitable for fixtures placed at the edge of wide paths, alleys, or roadways.
• Horizontal Angle: Light spreads up to 1.5 times the height of the fixture. A 10-meter high fixture will cast light about 15 meters wide.

3. Type III Light Distribution

• Description: Provides a wider distribution suitable for roadways and general parking areas.
• Horizontal Angle: The light covers an area about 2.75 times the height of the fixture. A fixture mounted at 10 meters high will cover approximately 27.5 meters.

4. Type IV Light Distribution

• Description: Known as forward throw or asymmetric, these fixtures provide a rounded light pattern with minimal light falling behind the fixture.
• Horizontal Angle: Light distribution is similar to Type III but focuses more forward, making it suitable for mounting on walls or illuminating specific areas.

5. Type V Light Distribution

• Description: Features a circular or square pattern, providing uniform light distribution around the fixture.
• Horizontal Angle: Provides a 360-degree light distribution, ideal for large areas requiring even illumination, such as commercial parking lots and intersections.

The Role of Light Distribution Patterns in Horizontal Angles

Light distribution types directly relate to the horizontal angle of illumination, which is the extent of light spread from the fixture. The chosen distribution type affects the fixture’s placement and the spacing between fixtures to ensure even coverage and reduce dark spots.

• Type I fixtures are typically used for narrow spaces, where a focused light beam is essential.
• Type II fixtures are suitable for slightly wider paths and are often used at the edge of the area to be lit.
• Type III fixtures are ideal for medium-width roadways and parking areas, where a broader light spread is necessary.
• Type IV fixtures offer a broader, forward-focused light, useful for illuminating building perimeters and walls.
• Type V fixtures provide an even, circular distribution, perfect for large, open areas where uniform light is needed.

Understanding and Using Light Distribution Curves

Light Distribution Curves:

• Definition: These curves represent the intensity of light emitted from a fixture at various angles. They are typically displayed in polar or cartesian formats and help visualize how light spreads horizontally and vertically.
• Reading the Curves: The horizontal axis often represents the angular distribution of light, while the vertical axis shows the intensity. By analyzing these curves, you can determine the effective coverage area and intensity at different angles.

Determining Angle from Distribution Curves:

• To determine the angle of light distribution from a curve, identify the points where the light intensity drops to desired levels. This will help in understanding how wide or narrow the light beam is and its effectiveness for your application.
• The following picture is an example, which is the distribution curve of our SL-AIO-XC:

In the light distribution curve, the method for identifying the horizontal and vertical beam angles is as follows:

Horizontal Beam Angle: The horizontal beam angle is usually represented by the C0-C180 direction (the blue curve in the diagram). It indicates the light’s spread angle in the horizontal direction. On the light distribution curve, find the points at both ends of the blue line, from 0 degrees to the point where the light intensity drops to 50%. The angle between these two points represents the horizontal beam angle.

Vertical Beam Angle: The vertical beam angle is represented by the C90-C270 direction (the red curve in the diagram). It indicates the light’s spread angle in the vertical direction. Similarly, find the points on the red curve where the light intensity drops to 50%. The angle between these points represents the vertical beam angle.

In this diagram, you can see the label “Average Diffuse Angle (50%): 82.5°,” which indicates the average beam angle where the light intensity decreases to 50% of its maximum. The blue line in the figure reaches 70 degrees on both sides, because the horizontal beam angle is 140 degrees

To determine the specific horizontal and vertical beam angles, carefully observe the spread range of the C0-C180 (blue line) and C90-C270 (red line).

Optimizing Light Distribution for Your Needs

1. Assess Your Area: Evaluate the width and requirements of the area to be lit. Choose the distribution type that best matches the space dimensions and lighting needs.
2. Calculate Fixture Spacing: Based on the light distribution pattern and horizontal angle, calculate the spacing between fixtures to ensure adequate coverage and minimize shadows.
3. Avoid Light Waste: Select fixtures with the appropriate distribution type to avoid unnecessary light spillage and optimize energy efficiency.
4. Choose the Right Installation Position: Install fixtures in positions that maximize the effectiveness of the chosen distribution type, whether on poles, walls, or other structures.

Conclusion

Selecting the appropriate light distribution pattern is essential for achieving optimal lighting performance. By understanding and applying the principles of light distribution types and analyzing light distribution curves, you can enhance the effectiveness of your outdoor lighting design, ensuring well-lit, safe, and aesthetically pleasing spaces.

If you have any further questions or need assistance with your lighting design, feel free to reach out to us for expert advice and support.