LED Lifespan Glossary & Technical Reference

Lumen Maintenance

Lumen maintenance quantifies the percentage of initial light output an LED delivers after a set operational period. Unlike incandescent or fluorescent lamps, which burn out abruptly, LEDs experience a gradual reduction in brightness—a process called lumen depreciation. Lumen maintenance is expressed as a percentage (e.g., 90% after 25,000 hours means the fixture retains 90% of its original brightness at that time).

This metric is fundamental for applications requiring consistent illumination, such as airports, industrial spaces, or galleries. It enables facility managers to anticipate when to replace fixtures and budget for maintenance. Lumen maintenance is established through standardized laboratory testing (notably IES LM-80), where LEDs are operated for thousands of hours and measured at intervals. The collected data is then extrapolated using TM-21 methodology to predict long-term performance.

High lumen maintenance reduces long-term costs and ensures compliance with safety standards. For instance, the International Civil Aviation Organization (ICAO) mandates strict lighting levels for airfields, making lumen maintenance a critical factor in airside lighting selection. Ultimately, lumen maintenance ensures lighting systems provide predictable, reliable performance throughout their lifecycle.

L70, L80, L90 Ratings

L70, L80, and L90 are industry benchmarks indicating the percentage of original light output remaining after a specified number of operating hours. For example, L70 defines the point at which an LED emits 70% of its initial brightness; L80 and L90 correspond to 80% and 90%, respectively.

These ratings are calculated via extended testing and TM-21 projection based on LM-80 data. L70 is standard for general lighting, as the human eye usually detects a 30% loss as significant. For demanding environments like museums or airfields, L80 or L90 may be specified to ensure minimal degradation over time.

For example, an airfield LED with an L90 rating of 60,000 hours will maintain at least 90% brightness for that entire period, supporting safety and compliance. Carefully note whether a product’s rating refers to L70, L80, or L90, as this substantially impacts real-world performance and maintenance planning.

Catastrophic Failure

Catastrophic failure is the sudden, total loss of function in a lighting product—when a lamp ceases to emit any light. Traditional bulbs often fail this way, but LEDs are designed to minimize abrupt failures. However, catastrophic events can still happen due to driver failure, electrical surges, thermal runaway, solder joint fatigue, or physical damage.

The LED driver (power supply) is a frequent failure point, especially if exposed to heat or voltage spikes. Environmental stressors like water, dust, or mechanical shock can also cause sudden failure, particularly if the fixture lacks proper protection.

In safety-critical applications (airports, emergency exits), catastrophic failure risks are mitigated with redundancy and robust design. High-quality fixtures incorporate features like surge protection and thermal cutoffs. Regular maintenance and monitoring for flicker, dimming, or color changes help prevent unexpected outages.

Parametric Failure (Practical Failure)

Parametric failure, or practical failure, occurs when an LED fixture continues to work but no longer meets required performance standards—due to excessive lumen depreciation, color shift, or other deviations from specifications.

This type of failure is most relevant for LEDs, which rarely fail suddenly but may lose too much brightness or shift color. For example, a fixture dropping below its L70 or L80 threshold, or with an unacceptably low color rendering index (CRI), is considered to have failed parametrically.

In regulated industries like aviation, parametric failure can impact safety and compliance. Photometric testing or automated monitoring systems help identify when fixtures need replacement. Definitions of parametric failure vary: in museums, even slight color shifts may be unacceptable, while less critical areas tolerate more loss.

Addressing parametric failure requires not only replacement but root-cause analysis—such as checking for thermal issues or electrical problems.

Average Rated Life

Average rated life, or mean life, is the number of hours at which 50% of a lamp sample has failed (the B50 value). This measurement, common for incandescent and fluorescent bulbs, is less meaningful for LEDs, which rarely fail abruptly. Most LEDs will operate well beyond their average rated life, but with reduced brightness or altered color.

For LEDs, average rated life is usually supplanted by lumen maintenance metrics like L70, L80, and L90. In regulated settings, such as airfields governed by ICAO standards, average rated life is a historical reference, but current practice relies on photometric performance data. Be cautious comparing average rated life between traditional and LED products, as the criteria for “failure” differ.

Lumen Depreciation

Lumen depreciation is the gradual reduction in light output as an LED ages. This is the main mode of LED performance decline. Factors such as high operating temperature, electrical current, environmental conditions, and component quality all influence the rate of depreciation.

To measure this, manufacturers use LM-80 testing, recording luminous flux at regular intervals and projecting future performance via TM-21. In regulated environments (like airports), accurate predictions of lumen depreciation are critical for compliance.

Monitoring and planning for lumen depreciation enables facilities to maintain consistent lighting and replace fixtures before they fall below required levels.

Color Shift

Color shift is an unwanted change in the hue or chromaticity of an LED’s light as it ages. LEDs can experience gradual or sudden color changes, often due to degradation in the phosphor layer, lens materials, or the semiconductor.

This is measured with metrics like correlated color temperature (CCT) and CIE chromaticity coordinates. Even minor shifts can be problematic in applications like museums, retail, or aviation, affecting safety and aesthetics.

Causes include heat, UV exposure, environmental contaminants, or poor-quality materials. Monitoring color stability is crucial for regulated or high-visibility environments, and advanced products may provide extended color shift test data.

Useful Life

Useful life defines the period an LED product meets its application’s performance criteria—typically, until it falls below a set lumen maintenance threshold (L70, L80, L90) or exceeds acceptable color shift. LEDs may continue to emit light long after this point, but with insufficient output or poor color.

In regulated applications (e.g., ICAO airfields), useful life is reached when brightness or color no longer meets requirements, even if the LED still works. This concept is central to maintenance and cost planning.

Always verify the criteria used to define useful life for any product; many critical applications specify both lumen and color stability data.

LM-80 Testing

LM-80 is a standardized test (IES) for measuring LED lumen maintenance. LEDs are operated at multiple temperatures for thousands of hours, with light output measured periodically. LM-80 does not predict total lifespan, but provides data for TM-21 projections.

Manufacturers often supply LM-80 reports, documenting luminous flux, color stability, and operational conditions. Regulatory bodies, such as ICAO, require such documentation for approval. Always review LM-80 data carefully, ensuring laboratory conditions match real installations.

TM-21 Projection

TM-21 is the methodology for extrapolating long-term lumen maintenance from LM-80 data. Since LM-80 tests are limited in duration, TM-21 mathematically projects when an LED will reach its L70, L80, or L90 threshold.

TM-21 projections are considered reliable up to six times the LM-80 test duration. Regulatory agencies require TM-21-derived lifespans to ensure compliance over declared service intervals. Always confirm that TM-21 projections use robust, verified LM-80 data relevant to your installation environment.

How LED Lifespan Differs from Traditional Lighting

LEDs and traditional lighting differ significantly in their failure and operational characteristics. Traditional lamps often experience catastrophic failure and are rated by average life (B50). LEDs, however, rarely fail abruptly; instead, their service life is defined by gradual lumen depreciation (L70, L80, L90) and, sometimes, color shift.

Maintenance planning for LEDs focuses on periodic monitoring and proactive replacement, rather than waiting for complete failure. This improves safety and reduces unplanned outages, especially in mission-critical environments like aviation.

While LEDs may cost more upfront, their longer useful life and lower maintenance needs typically yield lower total ownership costs.

Factors Affecting Real-World LED Lifespan

Thermal Management (Heat Control)

Thermal management involves design features that dissipate heat from LEDs and their drivers. Heat is the chief enemy of LED longevity: high temperatures accelerate degradation of the semiconductor, phosphor, and electronics.

The junction temperature (where the chip connects to its substrate) is critical—each 10°C increase can halve expected life. Quality fixtures use extruded aluminum heat sinks, advanced materials, and optimized designs to maintain safe temperatures. Poor ventilation, high ambient heat, or improper installation can all cause rapid performance loss.

ICAO and other agencies specify maximum allowable temperatures for aviation and mission-critical lighting to ensure compliance and safety.

For further technical details, regulatory guidance, or help selecting the right LED solution for your facility, contact us or schedule a demo .