Buyers Guide to LED Street Lighting

LEDs Can Improve Street Lighting Performance

Street lights help illuminate walkways, driveways, and roadways so drivers, cyclists, and pedestrians can identify roadway features and potential hazards. Appropriate roadway lighting can support nighttime visibility and safety when it is designed for the roadway, traffic conditions, surrounding environment, and applicable municipal requirements.

The U.S. Department of Energy notes that LED lighting can reduce energy use compared with older lighting technologies, particularly when fixtures, controls, and lighting levels are properly selected. DOE’s LED lighting guidance emphasizes the importance of selecting efficient products and designing systems for the application. Actual energy savings depend on the existing system, LED luminaire wattage, operating schedule, controls, utility rate, and delivered lighting performance.

While brightness matters for street lighting, higher light output alone is not the solution. Excessive luminance, poorly aimed fixtures, inadequate shielding, or unsuitable optics can create disability glare, discomfort glare, unwanted light trespass, and uneven lighting. Key factors in street-lighting performance include:

• Luminaire lumen output and efficacy
• Roadway geometry, pavement reflectance, and surrounding surfaces
• Color-rendering performance and correlated color temperature (CCT)
• Mesopic vision considerations where applicable
• Average, minimum, and maximum illuminance or luminance criteria
• Lighting uniformity and fixture spacing
• Backlight, uplight, and glare control
• Mounting height, outreach, tilt, and luminaire distribution

LED luminaires can provide precise optical distributions and dimming capability, but optical performance varies by model. A properly selected LED street light may reduce glare and spill light compared with an older installation; it does not automatically do so simply because it uses LED light sources.

Brightness of Street Lights

The Angle Made by Light Above the Nadir

Nadir is the point directly below a luminaire. Angles from nadir describe the direction of light relative to vertical downward. Traditional luminaire cutoff classifications used limits on intensity at 80 and 90 degrees from nadir. These legacy terms may still appear in municipal specifications, although modern outdoor-lighting evaluations commonly use BUG (Backlight, Uplight, Glare) ratings and fixture-specific photometric data.

• Full Cutoff: 0% luminous intensity at 90° from nadir and no more than 10% of lamp lumens as candela at 80° from nadir
• Cutoff: no more than 2.5% of lamp lumens as candela at 90° from nadir and no more than 10% at 80° from nadir
• Semi-Cutoff: no more than 5% of lamp lumens as candela at 90° from nadir and no more than 20% at 80° from nadir
• Non-Cutoff: no specified intensity limits at 80° or 90° from nadir

Roadway-lighting practices such as IES RP-8 provide methods and recommendations for evaluating roadway visibility, illuminance, luminance, uniformity, glare, and other design considerations. A lighting designer should use the applicable edition of the relevant standard, local requirements, and fixture-specific photometric data when developing a municipal lighting plan.

Full-cutoff or low-uplight luminaires can help limit direct uplight when they are installed level and used with suitable optics. However, Dark Sky requirements vary by jurisdiction and program. A zero-uplight rating, proper aiming, appropriate output, shielding, and controls may all be relevant depending on the project.

Modern LED luminaires can provide directional distributions and optical control for outdoor applications. Review the luminaire’s IES photometric file, BUG rating, mounting arrangement, and installation instructions rather than relying only on a general cutoff description.

What Makes Full-Cutoff or Low-Uplight Lighting Important?

Limiting unnecessary uplight and spill light can support energy conservation, reduce skyglow, and help protect adjacent properties and sensitive environments. The appropriate lighting approach depends on the roadway, surrounding land use, local ordinances, and required visibility criteria.

Coastal, residential, environmentally sensitive, and astronomical-observation areas may have specific lighting restrictions. Verify applicable local ordinances, environmental requirements, and project specifications before selecting fixtures.

Various Luminaires and Their Light Footprint

Different roadway distribution types serve different applications. Type V distributions are generally symmetrical and may be useful for areas such as intersections, parking areas, and roundabouts. Type I distributions are narrow and elongated, often used for paths, sidewalks, and narrow roadway applications. The appropriate distribution depends on pole location, mounting height, roadway width, spacing, and the required lighting criteria.

The Challenge of Calculating Useful Light from Fixture Lumens

Lumens measure total luminous flux from a luminaire; they do not indicate how much light reaches the roadway or target surface. Delivered illuminance or luminance depends on luminaire optics, mounting height, tilt, pole spacing, roadway geometry, surface reflectance, obstructions, and maintenance factors. Fixture-specific photometric analysis is the appropriate way to evaluate a street-lighting layout.

Surface color and reflectance affect how objects appear under a light source. Low-pressure sodium lighting has a very narrow spectral output and poor color-rendering capability. White LED lighting generally provides broader spectral content and better color rendering than low-pressure sodium, but LED spectral power distribution and CRI vary by product.

Color Rendering Index (CRI) describes how faithfully a source renders colors compared with a reference illuminant. CRI is not a measure of lumen output or brightness, and higher CRI does not stimulate rod cells. At low light levels, visual performance can also be influenced by spectrum, adaptation level, contrast, glare, and the visual task. Future street-lighting capabilities may include:

1. Intelligent Lights

Compatible controls, motion sensors, photocells, and networked systems can adjust output based on schedules, ambient light, traffic activity, or other programmed conditions. Control strategies should maintain required visibility and comply with local operating requirements.

2. Multi-functional Lights

Some pole and luminaire systems can incorporate traffic monitoring, communications equipment, weather sensing, or other municipal technologies. Availability and compatibility depend on the specific fixture and pole system.

3. Solar Panels

Solar-powered street-lighting systems can reduce dependence on a utility connection in suitable locations. Battery capacity, solar resource, seasonal conditions, operating profile, maintenance access, and local permitting should be evaluated for each project.

The Right Light Dispersion for Street Lights

Proper fixture selection and installation can help control glare while providing appropriate roadway illumination. Glare is not determined by one universal angle. It depends on luminaire luminance, intensity distribution, mounting height, tilt, viewing position, roadway geometry, background brightness, and the observer’s adaptation level.

Both LED and high-pressure sodium (HPS) luminaires are available with different optical systems and distributions. Older, poorly shielded, misaligned, or incorrectly spaced fixtures of any source type can create glare, uplight, and light trespass. A well-designed LED retrofit may improve optical control and reduce energy use, but these results must be verified using the selected luminaire’s photometric data and a site-specific lighting plan.

Light outside the intended roadway or pedestrian area may be considered spill light or light trespass, depending on the project and local requirements. Appropriate optics, pole placement, shielding where suitable, dimming, and careful aiming can reduce unwanted light. No lighting technology guarantees that nearby homes will experience no light at windows; this must be evaluated for the actual installation.

Uniform Light Dispersion

Uniformity should be evaluated during design and verified as appropriate after installation. It depends on luminaire photometry, mounting height, pole spacing, roadway width, outreach, tilt, maintenance condition, and surrounding surfaces. Common evaluation metrics may include:

• Average-to-minimum illuminance or luminance ratio
• Maximum-to-minimum illuminance or luminance ratio
• Maximum-to-average illuminance or luminance ratio

The applicable metric and acceptable ratio depend on the roadway classification, design method, and governing specification. Good uniformity can reduce abrupt changes in adaptation and improve visual continuity, but it does not by itself eliminate glare. A qualified lighting plan should evaluate illuminance or luminance, uniformity, veiling luminance or glare criteria where applicable, and spill-light considerations together.

Comparison of High-Pressure Sodium and LED

Municipalities often evaluate HPS-to-LED conversions to reduce energy use, improve controllability, and address maintenance needs. Results vary substantially by existing equipment and by the replacement luminaire. A one-for-one wattage or lumen comparison is not sufficient because roadway performance depends on distribution, spacing, mounting arrangement, light loss factors, and the target lighting criteria.

The National Lighting Product Information Program (NLPIP) published early research on LED roadway lighting. Since LED technology, product testing, controls, and roadway-lighting practice have evolved significantly, current fixture specifications and photometric files should be used for a new project.

The DesignLights Consortium maintains qualification programs for eligible LED street lights and other lighting products. DLC qualification information addresses specified performance and efficiency criteria; it is not an electrical safety certification. Electrical safety listing should be verified separately, such as through an appropriate Nationally Recognized Testing Laboratory listing where required. UL’s lighting resources provide information about lighting-product safety evaluation.

1. Compare the proposed LED luminaire’s delivered roadway performance with the required lighting criteria, not only with the existing HPS fixture’s labeled lamp lumens.
2. Evaluate energy use using actual input wattage, operating hours, dimming schedules, and utility rates.
3. Review photometric files, distribution type, BUG rating, CCT, CRI, surge protection, ambient-temperature rating, controls compatibility, warranty terms, and maintenance requirements for the exact model.

LED conversion cost and payback depend on equipment cost, installation conditions, controls, energy rates, operating hours, utility incentives, maintenance practices, and the service life of the selected products. A project-specific life-cycle cost analysis provides a more reliable comparison than a universal payback or lifespan claim.

What Is the Cost of Street Light LED Conversion?

1. Initial Costs for Poles, Wiring, Fixtures, and Installation

Street-light installation cost varies widely. Major variables include pole type and height, foundation or embedment requirements, electrical service distance, trenching, utility coordination, traffic control, local labor rates, permitting, fixture selection, and site conditions. Structural capacity, pole condition, foundations, and wind loading should be reviewed by the responsible engineer or other qualified project authority where required.

Solar-powered alternatives may reduce or avoid a utility connection in suitable locations, but they require careful evaluation of solar availability, battery autonomy, seasonal performance, equipment location, and maintenance access.

2. Energy Consumption Cost

Energy cost is calculated from actual luminaire input wattage, annual operating hours, controls schedule, and local electricity rate. For example, a 100-watt luminaire operating 10 hours per night uses approximately 365 kWh per year before accounting for controls or driver losses. Its delivered roadway lighting performance cannot be determined from wattage or lumens alone.

3. Lamp, Driver, and Maintenance Costs

Maintenance costs may include lamp, driver, photocell or control component replacement; labor; lift equipment; traffic control; and disposal requirements. Costs vary by municipality, access conditions, asset-management practices, and equipment type. Networked controls can help identify outages and support maintenance planning, but they do not eliminate the need for field service.

Conventional HPS, metal halide, mercury vapor, and LED products have different lumen-maintenance characteristics and service requirements. Rated life is product-specific and may be expressed using different metrics, such as lamp life, driver life, or LED lumen-maintenance projections. Review manufacturer data for the exact luminaire, operating temperature, control profile, and warranty rather than assuming a universal service life.

Calculating the Replacement Cost of One Light Point

The cost to service one street-light point may include replacement components, labor, lift or bucket-truck access, traffic control, travel time, administrative costs, and disposal. The total can vary significantly by location and maintenance contract.

Budget planning should consider initial capital cost, energy consumption, scheduled and unscheduled maintenance, controls, utility incentives, financing, and expected service life. A life-cycle cost model should use documented local assumptions rather than generic national averages.

The following example illustrates how annual energy cost changes with input wattage. It is not a performance, lumen-equivalency, maintenance, or lifespan comparison. Actual roadway lighting results require a photometric design.

• Example LED Input Wattage: 100W
• Example Operating Time: 10 hours per night
• Example Annual Operating Hours: 3,650 hours
• Example Annual Energy Consumption: 365 kWh
• Example Electricity Cost: $0.10 per kWh
• Example Annual Electricity Cost: $36.50

For comparison, a 250W luminaire operating on the same schedule would use approximately 912.5 kWh annually and cost approximately $91.25 per year at $0.10 per kWh. This example does not account for controls, utility tariffs, demand charges, driver losses, maintenance, or differences in delivered roadway illumination.

Expert Support That Makes Your LED Conversion Decision Easier

LED Lighting Supply can help customers compare street-light products, review manufacturer specifications, and prepare photometric lighting plans using fixture-specific IES data. We can help identify products that match established project requirements for distribution, output, controls, voltage, environmental ratings, and other published specifications.

Our team can also help evaluate estimated energy use and life-cycle cost using the operating hours, electricity rates, maintenance assumptions, and application information supplied for the project. Final roadway-lighting design, electrical-code compliance, pole and foundation structural capacity, utility requirements, and approval remain the responsibility of the qualified design professional, electrical professional, authority having jurisdiction, or other responsible project authority.