Why Do Solar Street Lights Get Dimmer Over Time? Understanding LED Lumen Depreciation

Last summer, I received a complaint from a customer.

“Your solar street lights have only been installed for a year. Why are they getting dimmer? They were really bright when we first installed them, but now they’re barely brighter than candles!”

I went to the site to inspect the lights. The customer was right—the brightness had noticeably decreased.

My first thought was that the problem could be related to LED lumen depreciation, commonly known as light degradation. It’s a natural process that affects LED light sources as they age.

But the customer wasn’t convinced.

“I paid for high-quality lights. Why would they start losing brightness after just one year?”

His question made me realize something: many buyers understand the wattage and brightness of solar street lights, but few know what happens to LED performance after months or years of operation.

What Is LED Lumen Depreciation?

Simply put, LED lumen depreciation is the gradual reduction in light output as LED chips age.

It doesn’t necessarily mean the light has failed. Instead, the materials inside the LED gradually deteriorate under the combined effects of heat, electrical stress, and operating time.

Think about your smartphone screen. When it’s new, the display looks bright and clear. After several years of heavy use, the screen may not appear quite as bright as it once did, even at its maximum brightness setting.

LED street lights experience a similar aging process.

In the lighting industry, manufacturers use a testing method called IES LM-80 to measure how LED packages, arrays, and modules maintain their light output under controlled temperature and operating conditions.

The results can then be used with IES TM-21 to project long-term lumen maintenance.

One important performance indicator is L70, which represents the point at which an LED light source is expected to maintain 70% of its original luminous flux.

For example, an LED with an L70 rating of 30,000 hours is expected to maintain at least 70% of its initial light output up to that operating time, under the specified conditions.

If a street light operates for 10 hours every night, 30,000 hours is equivalent to approximately 8.2 years of operation.

However, this doesn’t mean every LED street light is guaranteed to last eight years. Actual performance depends on LED quality, operating temperature, driver reliability, and the design of the complete fixture.

For procurement teams evaluating long-term lighting performance, understanding these ratings is just as important as comparing initial brightness.

Why Do Some Solar Street Lights Lose Brightness So Quickly?

After years of working with solar street lighting projects, I’ve noticed that unusually rapid brightness loss often comes down to three main factors.

Poor Heat Dissipation

Heat is one of the biggest enemies of LED performance.

LED chips generate heat whenever they operate. If that heat isn’t effectively transferred away from the LED junction, the temperature increases and the components age faster.

In general, higher operating temperatures can significantly accelerate lumen depreciation, although the exact impact depends on the LED package, materials, and operating conditions.

Some low-cost manufacturers reduce production expenses by using thin aluminum housings or undersized heat sinks.

These designs may look acceptable when the lights are first installed. But during hot summer months, internal operating temperatures can become excessively high.

I’ve encountered lights where temperatures near the LED assembly exceeded 80°C.

Without adequate thermal management, prolonged exposure to high temperatures can shorten the useful life of the LED components.

This is particularly important for solar street lighting projects in Africa, Southeast Asia, and the Middle East, where high ambient temperatures and strong sunlight can place additional stress on outdoor equipment.

Unstable LED Drivers

LEDs generally require controlled current to operate efficiently and reliably.

A properly designed constant-current LED driver maintains the appropriate electrical output and protects the light source against operating conditions that could damage it.

When the driver is poorly designed or starts to deteriorate, the LED may receive inconsistent current.

This can lead to flickering, abnormal brightness changes, excessive heating, and premature component degradation.

For conventional grid-connected street lights, voltage fluctuations can be a contributing factor.

In solar street lights, similar concerns may arise from faulty LED drivers, unstable battery output, or controller problems.

That’s why it’s important to evaluate the driver and control system alongside the LED chips.

A reliable solar street light is only as good as the components working together inside it.

Low-Quality LED Chips

Not all LED chips are manufactured to the same standards.

Some inexpensive street lights use low-grade LED packages with inconsistent performance, lower luminous efficacy, and poor thermal characteristics.

These lights can appear impressively bright during initial demonstrations but lose output much faster than expected.

In some cases, noticeable brightness deterioration may begin within the first six months.

When comparing products, I always recommend asking suppliers for the LED manufacturer, component specifications, and available lumen maintenance test reports.

A low purchase price doesn’t necessarily translate into a low total project cost.

If hundreds of street lights require early replacement or maintenance, the savings from purchasing cheaper fixtures can disappear quickly.

How Can You Tell Whether LED Lumen Depreciation Is Normal?

This is one of the most common questions customers ask.

Some reduction in light output over time is expected, but the rate of depreciation varies depending on the LED and its operating environment.

In some installations, a small amount of initial depreciation may occur during the early operating period.

However, there is no universal rule that every new LED street light should lose 5%–10% of its brightness during the first three months or 3%–5% every year.

Those figures should not be treated as industry standards.

Instead, buyers should evaluate actual performance against the manufacturer’s stated lumen maintenance data, operating conditions, and warranty requirements.

If a street light loses more than 20% of its measured light output within six months, I would consider that a strong reason to investigate.

Possible causes include poor heat dissipation, defective LED components, driver problems, reduced battery capacity, or incorrect control settings.

It’s also important to understand that a dimmer solar street light doesn’t always mean the LED chips are aging.

A solar street light may reduce brightness automatically because of low battery voltage, energy-saving settings, or programmed dimming schedules.

Before replacing the LED fixture, check the entire system.

For additional troubleshooting guidance, see Clodesun’s article on how to improve the brightness of solar street lights.

How to Reduce LED Lumen Depreciation in Solar Street Lights

As a user or project owner, you can’t completely prevent LED aging.

However, you can reduce premature performance loss by choosing the right equipment and maintaining it properly.

Here are four practical recommendations.

Don’t Choose Street Lights Based on Price Alone

Solar street lights are designed for outdoor environments.

They must withstand high temperatures, heavy rain, strong winds, dust, and years of continuous operation.

Reliable materials and components cost money, especially high-quality LED packages, suitable heat sinks, dependable drivers, and weather-resistant housings.

While there’s no fixed industry rule requiring LED light sources to account for a particular percentage of the total product cost, extremely low prices should prompt closer inspection of component quality.

For municipal projects, residential developments, and bulk procurement, it’s often better to compare total lifecycle costs rather than purchase prices alone.

That includes installation, maintenance, replacement components, and expected operating life.

Check the Heat Dissipation Design

One of the easiest things to evaluate when selecting a solar street light is its housing and cooling structure.

A well-designed aluminum housing generally provides better heat transfer than a poorly designed plastic enclosure.

However, housing thickness alone doesn’t guarantee effective cooling.

What matters is how efficiently heat moves from the LED junction through the circuit board and thermal interface to the surrounding environment.

Look for properly designed heat sinks, appropriate thermal interface materials, and a structure that allows effective passive cooling.

Some higher-performance fixtures also use advanced thermal materials or heat-spreading components.

For buyers who want to understand what separates dependable products from low-cost alternatives, Clodesun’s guide to choosing good-quality solar LED street lights explains several important selection considerations.

Choose the Right LED Power

More watts don’t automatically mean better lighting.

For example, a 30W LED street light may provide sufficient illumination for certain rural roads, depending on installation height, road width, spacing, optical distribution, and required lighting levels.

Using a 50W or 60W fixture when the project doesn’t need that much output may increase energy consumption and thermal load without providing a meaningful benefit.

Higher operating temperatures can accelerate LED aging if the thermal design isn’t adequate.

That’s why I always recommend selecting LED power based on the actual lighting requirements rather than simply choosing the highest wattage available.

A proper lighting design should consider the required illuminance or luminance, uniformity, glare control, road geometry, and applicable project standards.

Clean and Maintain the Lighting System Regularly

Dust and dirt can affect the performance of solar street lights in several ways.

When dust accumulates on the solar panel, it reduces the amount of sunlight reaching the photovoltaic cells.

Less solar energy means less electricity available to charge the battery, which can cause the controller to reduce lighting output.

Dirt on the LED lens or protective cover can also reduce the amount of light reaching the road.

In some fixture designs, heavy dirt buildup around cooling surfaces may interfere with heat dissipation.

For many installations, inspecting and cleaning the system every six months is a useful starting point, although actual maintenance intervals should depend on local environmental conditions.

Projects in dusty, industrial, or desert environments may require more frequent inspection.

You can learn more about preventive maintenance in Clodesun’s guide on how to maintain solar street lights.

What Happened to the Customer Who Complained?

Let’s return to the customer I mentioned at the beginning.

After explaining how LED lumen depreciation works, I used a lux meter to check the lighting levels at the installation site.

The lights certainly appeared dimmer than when they were first installed.

However, the measured illuminance still fell within the requirements applicable to that particular project.

That didn’t mean we could ignore the complaint.

We continued checking the system and eventually agreed to replace the LED driver free of charge.

After the replacement, the brightness improved considerably.

This also showed that the problem wasn’t simply natural LED aging. The driver had contributed to the reduced output.

A few days later, the customer told me:

“If someone had explained these things when I bought the lights, I wouldn’t have been so upset. You work with lighting every day, but customers like us don’t understand all the technical details.”

His words stayed with me.

When we sell solar street lights, we often talk about impressive brightness, long operating life, and energy savings.

But we don’t always spend enough time explaining lumen depreciation, maintenance requirements, and the difference between expected aging and actual equipment problems.

That experience reminded me that customers deserve to understand not only what a street light can deliver on the first day, but also how it should perform after several years.

Final Thoughts

LED lumen depreciation is unavoidable, but premature brightness loss can often be reduced through good product design, proper component selection, and regular maintenance.

When purchasing solar street lights, don’t focus exclusively on wattage, initial brightness, or the lowest quotation.

Ask about thermal management, LED chip specifications, lumen maintenance data, driver quality, and warranty coverage.

For government procurement officers and EPC contractors purchasing hundreds or thousands of solar street lights, these details directly affect long-term project reliability and maintenance costs.

And if a street light becomes noticeably dimmer after installation, investigate the battery, controller, driver, optics, and LED light source before assuming the LEDs have reached the end of their useful life.

A good solar street light shouldn’t just look bright during installation. It should deliver dependable lighting performance for years to come.

Frequently Asked Questions About LED Lumen Depreciation

Why do solar street lights get dimmer after one year?

Solar street lights may lose brightness because of natural LED lumen depreciation, excessive operating temperatures, faulty LED drivers, battery deterioration, or controller settings. A noticeable reduction after just one year should be investigated rather than automatically considered normal LED aging.

What is LED lumen depreciation?

LED lumen depreciation is the gradual reduction in luminous flux produced by an LED light source over time. It occurs as the materials inside LED packages age under thermal and electrical stress. Unlike sudden component failure, lumen depreciation typically develops gradually.

How long can LED solar street lights maintain their brightness?

The answer depends on the LED components and operating conditions. Manufacturers often use L70 ratings to describe how long an LED light source is expected to maintain at least 70% of its initial light output. Complete solar street light performance also depends on battery life, driver reliability, thermal management, and maintenance.

What is the difference between LM-80 and TM-21?

LM-80 is a standardized testing method used to measure lumen and color maintenance of LED packages, arrays, and modules under controlled conditions. TM-21 uses LM-80 test data to project longer-term lumen maintenance. Neither method independently establishes the lifespan of an entire solar street light.

Can high temperatures cause solar street lights to lose brightness faster?

Yes. High LED junction temperatures can accelerate material degradation and reduce long-term lumen maintenance. Proper heat sinks, suitable housing materials, and effective thermal interfaces help maintain appropriate operating temperatures, particularly in hot climates.

Can replacing the LED driver restore solar street light brightness?

Yes, if the driver is malfunctioning or supplying incorrect current. Replacing a faulty driver may restore normal output. However, driver replacement cannot reverse permanent lumen depreciation that has already occurred inside the LED chips.

How can contractors check whether solar street lights have lost too much brightness?

Contractors can compare current lighting measurements with commissioning records and project requirements. Measurements should be taken under comparable operating conditions, using calibrated equipment and consistent measurement locations. Battery status, dimming settings, and the condition of the LED fixtures should also be checked.

What should buyers request from solar street light manufacturers to verify long-term performance?

Buyers should request LED specifications, relevant LM-80 reports, TM-21 lumen maintenance projections where available, thermal performance information, driver specifications, and written warranty terms. For large municipal or commercial projects, complete luminaire testing and project-specific lighting calculations can provide additional assurance.

Technical reference: The distinction between LM-80 LED component measurements, TM-21 projections, and complete luminaire reliability follows the Illuminating Engineering Society’s guidance on LED product lifetime prediction.