The Life of an LED: Why Yellowing Happens as LEDs Age

The Life of an LED: Why Yellowing Happens as LEDs Age

The Life of an LED: Why Yellowing Happens as LEDs Age

LEDs are known for their efficiency, long lifespan, and low maintenance—qualities that make them ideal for architectural and commercial lighting. However, over time, even the best LEDs undergo photometric and chromatic degradation. One of the most noticeable symptoms is yellowing: a shift from crisp white light to a duller, warmer hue.

Understanding this aging process is essential for ensuring lighting performance remains consistent over years of use—especially in design-sensitive environments such as galleries, retail, hospitality, and branded spaces.

Typical Lifespan of an LED Chip

Unlike traditional lighting that fails abruptly, LEDs exhibit gradual degradation. Their lifespan is commonly rated by how long they take to reach a certain percentage of their original luminous output:

  • L70: Light output falls to 70% of initial brightness (common industry benchmark).
  • L80 / L90: Higher standards used for professional or premium applications.

What Impacts LED Lifespan:

  • Junction Temperature: Excess heat accelerates degradation of both the chip and surrounding materials.
  • Drive Current: Overdriving LEDs (pushing higher currents for more brightness) increases stress and reduces life.
  • Material Quality: Inexpensive phosphors, substandard encapsulants, or low-quality optics will degrade faster.
  • Environmental Conditions: High humidity, dust, and UV exposure can all shorten operational life.

Typical Expectation: High-quality architectural LEDs can last between 25,000+ depending on application and usage. That's a significant improvement over traditional incandescent bulbs, which typically last only 750-2,000 hours.

However, visible colour shifts such as yellowing may appear well before lumen depreciation becomes noticeable.

1. Phosphor Degradation

How It Works:

Most white LEDs are actually blue LED dies coated with a phosphor material (usually YAG or mixed phosphors). This coating shifts the blue light spectrum into yellow and red wavelengths, resulting in “white” light.

Why It Yellows:

  • Heat exposure causes the chemical structure of phosphors to break down or crystallize.
  • UV radiation from the blue LED gradually degrades the phosphor layer.
  • Moisture and air exposure can also accelerate chemical aging of phosphor compounds.

Visual Effect:

  • The blue component diminishes faster than the yellow, causing a correlated colour temperature (CCT) drop.
  • Light appears warmer or amber, even if brightness remains high.

Design Insight: Yellowing due to phosphor degradation is particularly problematic in backlit graphics, gallery lighting, and high CRI environments, where precise colour fidelity is crucial.

 

2. Lens and Encapsulation Yellowing

What These Materials Do:

  • Encapsulants (silicone or epoxy resins) protect the LED chip and help direct light.
  • Secondary lenses or diffusers shape light output and manage glare.

Why It Yellows:

  • Photothermal aging (heat + light exposure) causes polymers to oxidize and discolour.
  • Silicone, though more stable than epoxy, still yellows at elevated temperatures or under prolonged UV.
  • Low-quality plastics can off-gas, degrade, or become cloudy, especially in sealed fixtures.

Visual Effect:

  • A yellowish tint filters all light output, altering both CCT and CRI.
  • Loss of transparency reduces luminous efficacy and increases perception of dimming.

Design Insight: Always assess material resistance ratings (UV, thermal, chemical) when specifying LEDs for outdoor, display, or hospitality environments.

 

3. Thermal Degradation

Why Heat Is the #1 LED Killer:

LEDs are more efficient than traditional bulbs but still convert up to 40% of energy into heat. If not dissipated properly, this heat can accumulate and degrade internal components.

Effects of Excessive Heat:

  • Shortens LED chip lifespan by damaging internal die bonding.
  • Accelerates phosphor breakdown and lens yellowing.
  • Affects solder joints, leading to early electronic failure.

Heat Sources:

  • Poor fixture design with no heat sinks or airflow.
  • High ambient temperatures, especially in enclosed architectural elements.
  • Incompatible dimming or driver setups causing overcurrent.

Design Insight: Always verify that LED luminaires include active or passive cooling systems, especially in applications like recessed ceilings, cove lighting, or warm climate installations.

 

4. Driver and Circuit Degradation

What the Driver Does:

LEDs require constant current drivers to maintain consistent performance. These drivers convert mains AC into regulated DC power suited to the LED chip.

Why It Causes Yellowing:

  • Aging components like electrolytic capacitors degrade under heat, leading to unstable output.
  • Fluctuations in power may underdrive or overdrive the LED, accelerating phosphor or chip wear unevenly.

Visual Effect:

  • Colour shift is not uniform—some LEDs in a cluster may appear warmer or dimmer than others.
  • In systems with mixed age drivers, visual inconsistency becomes obvious over time.

Design Insight: Ensure driver and LED compatibility and look for drivers with high MTBF (mean time between failures) ratings for long-term reliability.

 

5. Environmental Contaminants

Sources of Contamination:

  • Sulphur from nearby rubber materials or construction adhesives.
  • Chlorine or cleaning agents in pool or spa environments.
  • Airborne particulates in urban, industrial, or coastal settings.

What Happens:

  • Surface reactions cause tarnishing or corrosion of the chip or substrate.
  • Diffusers and lenses may become cloudy or yellow due to chemical exposure.

Visual Effect:

  • Yellow film or dust build-up reduces transparency and alters light colour.
  • May also impact beam uniformity and brightness.

Design Insight: Use fixtures with IP-rated enclosures and corrosion-resistant materials in challenging environments—especially in swimming pools, kitchens, marine, or urban exteriors.

 

Conclusion: Designing for Light That Lasts

LEDs don’t just need to stay on—they need to stay visually consistent. Yellowing is a slow but cumulative process that can undermine the look and feel of an architectural space. While lumen output may still meet spec, aesthetic and functional performance degrades in ways that affect user experience, mood, and design perception.

By understanding how and why LEDs degrade:

  • You’ll make smarter fixture specifications
  • Ensure long-term lighting consistency
  • Avoid costly mid-life replacements

Design with intention. Specify for longevity. Preserve the light quality your space was meant to have.