What Are Light Distribution Types for Street Lights?

Ever noticed how streetlights illuminate the ground as you walk at night? It’s easy to overlook, but there’s real science behind it. The way street lighting is designed to spread light is a form of controlled distribution that keeps roads and sidewalks safe and comfortable for both pedestrians and drivers.

Different streets require distinct lighting patterns. A residential area doesn't need the same level of lighting as highways or parking lots. Therefore, choosing the proper light distribution is necessary. Choosing the right one isn't about brightness, but about reducing dark spots and energy consumption.

Now we'll go through the types of light distribution and how to select the right one based on different applications.

What Is Light Distribution?

Light distribution describes how light spreads from a fixture. It can be directional or multidirectional. That light comes from special lenses and reflectors of the fixture control. Some send it far down the road while others spread it wide across multiple lanes. This control is called light distribution.

Putting light in the right place means you need less energy to light your streets. You also get fewer dark spots and less glare in drivers' eyes. Thus, good light distribution makes streets safer while using less electricity.

Types of Light Distribution

Street lights come in five main distribution types. Each one has a specific job. Here are the five types of light distribution:

Type I Distribution: Directs light in a narrow, elongated pattern along both sides of a roadway. It is typically applied on narrow roads or sidewalks where the width is similar to the mounting height of the light pole.

Type II Distribution: Reaches an area 1.75 times the mounting height; an ideal choice for residential streets and commercial areas.

Type III Distribution: Throws light even farther from the pole, covering up to 2.75 times the mounting height. Major roads with three or more lanes require this type. It's the workhorse of highway and arterial street lighting.

Type IV Distribution: It has a unique forward throw pattern. It is commonly used along the edges of larger spaces to illuminate areas away from the mounting location, such as parking lot perimeters.

Type V Distribution: Spreads light equally in all directions; suitable for plazas, intersections, or large parking lots.

Why Choosing the Right One Matters?

Choosing the wrong distribution type wastes energy and money. Pick the right type by understanding power density, uniformity, and glare.  

• Power Density: Use lower wattage fixtures. A 100-watt fixture with the correct distribution performs the same function as a 150-watt fixture, saving 50 watts per pole.
• Uniformity: Light falls evenly from pole to pole, and drivers can see the area clearly. The wrong choice creates bright spots under poles and dark valleys in between.
• Glare: Too much light hitting drivers' eyes directly makes driving dangerous. The correct distribution puts light on the road, not in people's faces. Type III lights reduce glare on highways. Type V lights prevent glare in parking lots.

How to Select the Right Distribution According to Different Applications?

Choosing the correct light distribution isn't guesswork. You have to consider several factors when selecting the appropriate distribution.

Road Width and Configuration

First, measure your road width. A narrow two-lane road and a six-lane highway require different lighting. Count the lanes. Add the width of the driving surface and sidewalks.

Type I or II is ideal for 25-foot-wide roads, Type II and III work for 25 to 40 feet, and those wider than 40 feet require Type III.

Mounting Height

The height of your poles changes everything. Higher poles need wider distribution patterns to reach the edges of the road. However, lower poles can use narrower patterns.

Here's a simple rule: Divide your road width by your mounting height. 

Pole Spacing

How far apart are your poles? It affects which vertical distribution you need. Vertical distribution refers to how far light travels along the street from each pole. Poles spaced at 2.5 to 3 times the mounting height work with short distribution. Spacing of 3.5 to 4 times the height calls for medium distribution. Anything beyond 4 times needs a long distribution.

Specific Applications

Select the appropriate light distribution type for each application. That's how it properly spreads light.

• Main Roads and Highways: These require Type III distribution with Medium or Long throw. A Type IIIM or IIIIL pattern provides uniform light across multiple lanes.
• Residential Streets: Type II distribution works best. That's because the streets are narrower and traffic moves slowly.
• Parking Lots: Type IV works here; install fixtures along the edges, with Type IV distribution pointing inward. For the centre areas, use Type V for even coverage. This combination eliminates dark corners where people feel unsafe.
• Sidewalks and Pedestrian Areas: Type I or Type II with asymmetric distribution works well. Asymmetric means the light favours one side over the other. It illuminates the walkway without falling onto adjacent properties.
• Intersections: Type V provides the best coverage. Light spreads equally in all directions. Drivers see crossing traffic and pedestrians clearly.

Light Distribution Performance Data

MH = Mounting Height

Wrapping Up

Light distribution affects every street light project. The right choice improves safety, reduces energy costs, and creates comfortable outdoor spaces. The wrong choice wastes money and creates problems.

Start by measuring your site carefully. Know your road width, mounting height, and pole spacing. Consider the area you're lighting. Then match these factors to the distribution types.

Lighting design isn't about picking fixtures; it's about creating solutions. CHZ Lighting provides the right distribution lights at affordable prices to help you get the benefits for years to come.

FAQs

1. Can the Same Street Light Model Offer Different Distributions?

Yes, most modern street lights offer multiple distribution options. The light fixture stays the same; the lens or optic inside changes; manufacturers design fixtures with interchangeable optics.

2. What Tools Help Determine the Right Light Distribution Type?

Several tools make light distribution easier. Some of these include:

• Lighting software like DIALux or AGi32 models your site. Input specs and test different distributions.
• In simple calculation methods, the mounting height method is one approach. Divide your road width by mounting height. This ratio points you toward the right distribution category.
• IES files detail how a fixture emits light. Professionals use them to design accurate lighting plans.