LED (light emitting diode) color shift refers to the change in color that can occur in LED lights as factors like voltage, temperature, and viewing angle change. Understanding LED color shift is important for choosing the right LED products and getting the desired lighting effect.
How LEDs Produce Light
LEDs produce light through a process called electroluminescence. When voltage is applied to an LED, electrons flow through a semiconductor material. As the electrons move between energy levels, photons are emitted, producing visible light.
The color of light emitted depends on the semiconductor material used in the LED. Materials like gallium arsenide phosphide (GaAsP) and indium gallium nitride (InGaN) allow LEDs to emit different colors from red to blue and white.
What Causes LED Color Shift?
Several factors can cause the light color emitted by an LED to change or shift:
- Voltage – Higher voltage generally causes LEDs to emit at a higher color temperature or more blue light. Lower voltage causes more red or warm light.
- Junction Temperature – Increased junction temperature shifts light color towards red/warmer tones. Lower junction temperature leads to more blue/cool light.
- Viewing Angle – LEDs look warmer or redder when viewed off-angle compared to straight-on.
- Aging – LED light color tends to shift yellow and red over time as materials degrade.
- Manufacturing Variation – Different batches of LEDs vary slightly in their colors due to material differences.
Voltage-Based Color Shift
One of the most significant factors causing LED color shift is voltage. The voltage applied to an LED impacts the intensity of light emitted at different wavelengths, changing the overall color.
Higher voltage generally increases shorter wavelength blue light output more than longer wavelength red light. This makes the LED appear cooler or more blue at higher voltages. Lower voltages have the opposite effect – reducing blue light and making the LED appear more red or warm.
| Voltage | Color Shift |
|---|---|
| Higher Voltage | More blue light, cooler color temperature |
| Lower Voltage | Less blue light, warmer color temperature |
The amount of voltage-based color shift depends on the LED material and design. But for a typical phosphor-based white LED running on 12V, the color temperature change between 10V and 14V can be 500-1000K or more.
Thermal Effects on Color Shift
LED junction temperature also significantly impacts color. The junction is where light is generated in an LED, and its temperature rises due to electrical resistance during operation.
Higher junction temperature reduces the difference in energy between quantum states in the LED semiconductor material. This decreases blue light emission more than red light, causing an overall shift to warmer tones at higher temperatures.
Properly designed LED circuits use heat sinks and other cooling methods to maintain operation at lower junction temperatures. This helps maintain consistent, cooler color temperature over the LED’s lifetime.
Viewing Angle and Color
The emitted color of an LED also changes based on the viewing angle, or angle from which it is observed. LEDs appear warmer or more reddish when viewed from wider angles off the principal axis and cooler or more blue when viewed directly on-axis.
This effect occurs because LEDs emit different wavelengths of light in different spatial patterns, and the relative intensity of different colors changes with angle. Using diffusers and other optics can help reduce angle-based color shift in LED lighting applications.
Color Shift Over LED Lifetime
LED light color tends to shift toward yellow and red over time. This is due to several factors:
- Phosphor degradation – Phosphor converted white LEDs use phosphor coatings to convert blue to other colors. These degrade over time.
- Epoxy yellowing – The epoxy resin used in LEDs can gradually yellow with heat and radiation exposure.
- Reflector erosion – Some LEDs use metal reflectors that erode over long operation.
Higher quality LEDs exhibit less color shift over time. But in general, the effect is greater in cheaper LED products with less stable materials and structures. Color shift may be more noticeable in cooler white LEDs as they shift warm.
Accounting for LED Color Shift
Understanding how LED color behaves and shifts with different factors allows designing lighting setups and choosing LED products to achieve the desired effects:
- Choose LEDs rated for adequate voltage range and temperature conditions.
- Select LEDs with optics to control beam angle if angle-based shift is undesirable.
- Allow for some warm color shift over lifetime, or choose LEDs with better lifetime color stability.
- Sample and bin match LEDs to minimize variation between batches/fixtures.
With careful selection and design, LED color shift can be minimized or controlled to take advantage of its benefits in tunable and dynamic lighting applications.
Applications Benefiting from LED Color Shift
While LED color shift is undesirable in some lighting uses, the ability to intentionally alter light color by modifying drive conditions allows unique effects and applications:
- Tunable white lighting – Varying LED voltage produces adjustable color temperature for customized ambience.
- Dynamic color effects – LED color can be modulated for lighting displays and mood lighting.
- Plant growth lighting – Shifting from cool to warm white during growth cycles may benefit plants.
- Indicators – Color shift can provide visual indication of temperature or voltage.
With creative drive electronics and optics, LED color shift opens up possibilities for innovative lighting solutions.
Key Takeaways on LED Color Shift
The key points to understand about LED color shift include:
- Voltage, temperature, viewing angle, and aging all impact emitted LED color.
- Higher voltage and lower temperature cause cooler, more blue light.
- LEDs appear warmer when viewed off-axis vs. straight-on.
- LED light tends to shift warmer over lifetime as materials degrade.
- Color shift can be minimized through careful LED selection and design.
- Color shifting properties allow for tunable white and dynamic lighting applications.
Considering the operating conditions and desired lighting effect allows appropriately accounting for color shift in LED lighting design. Both minimizing and utilizing color shift have roles in creating high quality, customizable LED illumination.