What Do L70, L80, and L90 Mean in LED Lighting? Understanding Lumen Maintenance

Part 2 of our four-part commercial LED lifespan series. Click here to review Part 1.

In commercial lighting specifications, “L” identifies lumen maintenance: the percentage of an LED’s original light output remaining after a stated number of operating hours. Also called brightness retention, this describes how much light the LED still produces compared with when it was new. L70 indicates 70% retention, L80 indicates 80%, and L90 indicates 90%.

These ratings help evaluate useful life, meaning the operational period before lighting falls below the levels required for its application. Useful life differs from catastrophic failure, which occurs when an LED or another component fails completely and stops producing light. A fixture can remain operational while becoming too dim for the space it serves.

Key Takeaways

• L70, L80, and L90 identify retained light output and must be paired with operating hours.
• Higher retention indicates stronger projected brightness maintenance when hours and operating conditions match.
• LM-80 measures LED component performance; TM-21 uses those measurements to project future output.
• Component lumen maintenance does not establish complete fixture reliability or guarantee a failure date.
• Commercial lighting plans should account for declining output before illumination falls below required levels.

What Is LED Lumen Maintenance?

LED lumen maintenance measures retained light output against the source’s initial output. Lumens measure the total visible light a source emits.

LED lumen depreciation describes the corresponding loss. A source with 80% lumen maintenance has experienced 20% lumen depreciation.

Calculate retention using this formula:

Lumen Maintenance (%) = (Current Lumen Output ÷ Initial Lumen Output) × 100

For example, a source that initially produces 10,000 lumens and later produces 8,000 lumens has 80% lumen maintenance.

What Is the Difference Between L70, L80, and L90?

The number after “L” identifies the percentage of original light output remaining at the stated operating time.

Rating	Maintained Output	Lumen Depreciation	Example Specification
L70	70%	30%	L70 at 100,000 hours
L80	80%	20%	L80 at 75,000 hours
L90	90%	10%	L90 at 50,000 hours

These specifications are illustrative, not universal product benchmarks.

An L70 rating of 50,000 hours means the source is projected to reach 70% of its initial output at approximately that operating time under the stated conditions. It does not remain at full brightness until that hour and suddenly become dimmer.

For the same source and conditions, L90 is generally reached before L80, followed by L70.

Is L80 Better Than L70?

An L80 LED rating indicates better projected brightness retention than L70 when both apply to the same operating hours and comparable conditions.

However, an L80 claim at 30,000 hours cannot be directly ranked against an L70 claim at 100,000 hours. Compare the percentage, hours, temperature, and supporting data together.

What Does L70B50 Mean on a Specification Sheet?

Specifications sometimes pair a lumen maintenance threshold, written generally as Lp, with a population-based Bx rating.

For example, L70B50 at 50,000 hours describes a projected median lumen maintenance life: approximately half the relevant population remains at or above 70% of initial output at that time, while half falls below it.

The B value addresses variation in gradual depreciation. It generally excludes abrupt failures and does not mean every finished fixture was physically tested for the full stated lifetime. Confirm whether the declaration applies to LED modules or complete fixtures.

Why Do LEDs Gradually Lose Light Output?

LED light output degradation develops as the semiconductor and materials within the LED package age. Operating temperature and electrical current influence the rate of deterioration.

Thermal management helps move heat away from the LEDs. Poor heat dissipation or operation beyond the fixture’s temperature rating can accelerate aging. Temperature fluctuations can also change immediate output and contribute to long-term stress.

Dust accumulation and deteriorating lenses can further reduce delivered illumination. These losses occur alongside LED component depreciation and require separate consideration.

How Does Lumen Maintenance Change a Fixture’s Output Over Time?

Consider a fixture that initially delivers 20,000 lumens. This hypothetical timeline illustrates its output at successive retention thresholds.

Illustrative Operating Point	Brightness Retained	Calculated Output
New installation	100%	20,000 lumens
30,000 hours	90%	18,000 lumens
60,000 hours	80%	16,000 lumens
90,000 hours	70%	14,000 lumens

These hours are examples, not product predictions. Actual depreciation is generally non-linear and depends on operating conditions, including thermal fluctuations. The “bathtub curve” describes changing failure rates across a product population, rather than the shape of an individual LED’s brightness decline.

This simplified example assumes fixture output follows LED source retention proportionally, without additional dirt, optical losses, or component failures.

How Do LM-80 Testing and TM-21 Projections Work?

The Illuminating Engineering Society (IES) publishes methods that support consistent measurement and projection of LED lumen maintenance.

Comparison	LM-80	TM-21
Method	Physical laboratory testing	Mathematical projection protocol
Main purpose	Measure output and color maintenance over time	Estimate future lumen maintenance
Evidence used	Measurements from LED samples under controlled conditions	LM-80 measurement data
Main limitation	Evaluates LED components rather than complete fixture reliability	Estimates performance beyond measured hours within reporting limits

What Is LM-80 Testing?

IES LM-80 measures the light output and color maintenance of LED packages, arrays, and modules at controlled temperatures and electrical currents.

Reports commonly include 6,000–10,000 hours or more of observations. These measurements document performance during the test period; they do not independently establish a complete fixture’s operating life.

What Is TM-21 Testing?

Although often called “TM-21 testing,” IES TM-21 is a calculation method that projects long-term lumen maintenance from LM-80 data.

Its reported projection limit is no more than six times the underlying test duration, with applicable sample-size and method requirements. For example, 10,000 hours of qualifying measurements can support a reported projection up to 60,000 hours.

Claims beyond the applicable limit are extrapolations outside TM-21 reporting limits and should not be presented as verified TM-21 results. Buyers should also confirm that the projection matches the LEDs’ operating temperature and current within the proposed fixture.

Does an L70 Rating Predict Complete Fixture Reliability?

An L70 rating does not cover every way a fixture can fail.

Finished fixtures also contain drivers, connections, lenses, seals, and other components. A failed driver can stop illumination while the LEDs still retain substantial output. Moisture intrusion, electrical damage, and optical deterioration can also shorten service life.

Review component projections alongside fixture construction, environmental ratings, driver information, and warranty terms.

Frequently Asked Questions

Does L80 mean an aging LED uses 20% less electricity?

No. A 20% reduction in output does not establish an equivalent reduction in electricity consumption. An aging fixture may produce fewer lumens while drawing approximately the same power.

Can cleaning restore lost LED brightness?

Cleaning can recover light blocked by dirt on accessible optical surfaces. It cannot reverse aging within the LED package. Follow the manufacturer’s cleaning instructions.

Are lumen maintenance percentages the same as foot-candles?

No. Lumen maintenance compares source output over time. Foot-candles measure light reaching a surface, which also depends on mounting height, spacing, beam distribution, and surrounding surfaces.

Plan for the Light Your Facility Will Need Over Time

Warehouses need sustained visibility for picking and movement. Retail spaces rely on adequate illumination for merchandise and navigation. Parking areas need sufficient coverage for pedestrians, vehicles, and potential hazards.

Lighting designers account for declining illumination through a Light Loss Factor (LLF), which combines relevant allowances such as lumen depreciation and dirt accumulation. For example, an overall LLF of 0.80 means the design anticipates 80% of initial calculated illumination under the assumed conditions. It is not automatically equivalent to an L80 rating.

Contact Action Services Group to evaluate your lighting and plan an LED upgrade that supports adequate illumination, practical maintenance, and long-term facility performance. Reach out today by calling 610-558-9773, emailing [email protected], or scheduling a call that fits your needs by clicking the button below.