When designing effective lighting systems, one term you’ll inevitably encounter is “beam spread.” But what exactly does it mean, and why does it matter? Whether you’re an electrician, contractor, or facility manager, understanding beam spread is crucial for creating functional, well-lit spaces. This guide to understanding and measuring beam spread will walk you through the basics, from how it works to practical tips you can apply to your lighting projects.
By the end, you’ll know how to measure beam spread accurately, the factors that affect it, and how to optimize it for your installations. Plus, we’ll explore examples to see these calculations in action. Lighting up a room (or a street!) has never been clearer.
Understanding Beam Spread: The Basics and How It Works
Beam spread, in simple terms, refers to the width of light emitted from a source. Imagine turning on a flashlight—the beam spread is the cone of light projected outward. It determines how much area the light will cover.
The concept becomes especially important when selecting fixtures for specific tasks or environments. A narrow beam works best when focusing on a small target, while a wider beam is ideal for evenly lighting a larger area. Understanding this ensures you choose lighting fixtures that align with your space’s practical and aesthetic needs.
There are two different ways to define beam spread:
- The NEMA classification system uses degrees to define how narrow or wide a beam of light appears.
- The IES light distribution system provides a shape-based method of categorizing beam spread.
IES Light Distribution Classifications
The IES classification system categorizes beam spread by the pattern a light produces. There are five different patterns ranging from Type I to Type V.
- Type I offers a narrow, elongated beam that spreads symmetrically on both sides of the fixture. It’s ideal for pathways and sidewalks where lighting a long, narrow area is key.
- Type II casts light in a slightly wider pattern, covering a larger area than Type I. This is perfect for small roadways, alleys, or larger sidewalks
- Type III delivers a rectangular and more forward-reaching beam, making it effective for parking lots, driveways, and building perimeters. It can light large, open spaces.
- Type IV pushes light outward in a semicircular pattern, often mounted on buildings to illuminate outdoor areas and small parking lots.
- Type V provides a circular distribution of light, radiating equally in all directions. It’s ideal for open areas such as parking lots and intersections.
NEMA Beam Spread Classifications
The NEMA classification system splits beam spread into seven primary types based on its degree range. It’s most commonly used for selecting spotlights and floodlights.
- NEMA 1: Very Narrow (10 to 18 degrees)
- NEMA 2: Narrow (18 to 29 degrees)
- NEMA 3: Medium Narrow (29 to 46 degrees)
- NEMA 4: Medium (46 to 70 degrees)
- NEMA 5: Medium Wide (70 to 100 degrees)
- NEMA 6: Wide (100 to 130 degrees)
- NEMA 7: Very Wide (130 degrees or more)
Fixtures with a narrow beam spread create focused lighting, perfect for highlighting artwork in galleries. Medium beam spreads are more versatile and provide balanced lighting that’s useful when creating ambience in restaurants or hospitality spaces. Wide beam spreads are best for general lighting needs in event venues or industrial spaces, covering large areas evenly.
Measuring Beam Spread: Tools and Techniques
To design effective lighting systems, you need to measure beam spread accurately. Two common methods include using the beam angle formula or a professional light meter. Let’s break down the most widely used option—the formula.
The Beam Angle Formula
The simplest formula for calculating beam spread is:
Beam Spread = Beam Angle × 0.018 × Distance
Here’s how it works:
- Beam Angle is the width of the light beam at its brightest point (measured in degrees).
- 0.018 is a conversion factor used to determine the spread.
- Distance is how far the light travels from the fixture to the surface being lit.
Example 1:
Imagine that the beam angle of a spotlight fixture is 30 degrees. Let’s say that the distance between the fixture and the wall it’s highlighting is 10 feet.
Using the formula: 30-degree beam angle × 0.018 × 10 feet = 5.4 feet
The light will cover a 5.4-foot diameter area 10 feet away.
Example 2:
- Beam Angle = 50 degrees
- Distance = 8 feet
Using the formula: 50-degree beam angle × 0.018 × 8 feet = 7.2 feet
At 8 feet, the light will illuminate an area 7.2 feet across.
Using a Professional Light Meter
While less common, a professional light meter can measure beam spread by analyzing the light intensity at various points. This method is typically used in advanced scenarios or when you require greater accuracy.
Factors Affecting Beam Spread
Several factors influence beam spread, so you must consider these variables during light fixture selection.
Type of Light Source
LEDs often have a sharper, more directed spread compared to traditional bulbs. This makes them ideal for applications such as task lighting or directional accents.
Lens Design
The shape and material of the fixture’s lens affect the distribution of light. A diffused lens, for instance, can widen the beam spread.
Indoor vs. Outdoor Use
Indoor setups often require controlled beams for focused illumination, while outdoor parking lot lighting benefits from wider spreads for consistent coverage and visibility.
Mounting Height
Keep in mind how the distance of the fixture from the surface will affect the spread.
Understanding these factors helps you optimize your design decisions for the intended environment.
Practical Tips for Optimizing Beam Spread in Lighting Installations
1. Consider Mounting Height
The height at which you install a fixture significantly changes its beam spread. Higher placement results in a wider spread but lower intensity light. Closer placement creates a narrower beam spread with higher brightness.
2. Evaluate Spacing Between Fixtures
If you’re handling an outdoor LED street light project, space out the fixtures evenly for consistent coverage. Placing them too close together will create excessive brightness in certain spots, while fixtures that are too far apart will have shadows.
3. Use Beam Spread Charts
Many manufacturers provide beam spread charts that show the light coverage at various distances. Use these charts to plan your fixture placement.
4. Test Before Final Installations
Whenever possible, test the fixtures in the environment before finalizing the setup. Adjust angles and placements to achieve your desired lighting effect.
Key Takeaways for Beam Spread Mastery
This guide to understanding and measuring beam spread equips you with the essential knowledge to make informed lighting decisions. By applying the techniques and tips outlined here, you can ensure every project—from accent lighting in a gallery to an outdoor street light installation—achieves its goals.
Mastering beam spread doesn’t just improve lighting quality—it also enhances safety, aesthetics, and user satisfaction. If you’re ready to see better results in your lighting designs, put these insights to work today!
