November 26, 2024
Scientists Use Custom LEDs to Mimic Natural Light Indoors
Compared to standard white LEDs, TADF-WLED outperforms in both visual and circadian metrics
A recent study published in Scientific Reports has added to the discussion of human-centric electric light by introducing a color-tunable LED-based light source engineered to replicate the spectral power distribution (SPD) of natural daylight. The research, conducted by Georgia Tech researchers, demonstrates a novel hybrid LED system utilizing thermally activated delayed fluorescence (TADF) dyes fabricated via additive manufacturing. The findings address critical challenges in electric lighting, including visual fidelity, circadian alignment and sustainability.
Modern lifestyles have significantly reduced exposure to natural daylight, with the average individual in developed nations spending over 90% of their life indoors. Daylight plays a vital role in regulating circadian rhythms, which influence sleep, mood, and overall health. However, traditional electric lighting systems, including state-of-the-art LEDs, fail to fully mimic the dynamic spectral qualities of natural daylight. This shortfall has been linked to various health issues, such as disrupted sleep cycles, metabolic disorders and increased risks of chronic diseases.
To mitigate these effects, human-centric lighting solutions aim to replicate daylight's evolving SPD throughout the day. This involves achieving a balance between visual quality — measured by metrics such as color rendering index (CRI) and correlated color temperature (CCT) — and circadian effectiveness, assessed through metrics like melanopic equivalent daylight illuminance (melanopic EDI).
Study Claims LED Innovation Mimicking Daylight Spectra
The hybrid light source introduced in the study is built on a violet-emitting LED (VLED) platform. It uses a linear combination of light-converter channels containing TADF dyes, which were fabricated through additive manufacturing. This design allows precise tuning of SPDs across a wide range of CCTs (4,277 K to 22,333 K), simulating various daylight conditions such as clear skies, sunsets, and overcast days.
The study yielded critical insights into the performance of the TADF-WLED technology across visual, circadian, and energy efficiency domains. These findings demonstrate its superiority over existing LED systems in approximating the qualities of natural daylight:
- Color Rendering and Fidelity
The TADF-WLED achieved exceptional values for the two primary color-rendering metrics defined by the Illuminating Engineering Society (IES):
- Color Fidelity Index (Rf): Maintained values within 7% of reference daylight SPDs, signifying accurate reproduction of natural hues.
- Color Gamut Index (Rg): Fell within 3% of the reference, ensuring no over- or under-saturation of colors.
These metrics highlight the system’s ability to render colors in a manner that closely mimics natural daylight, surpassing existing commercial LEDs.
- Circadian Lighting Efficiency
The TADF-WLED excelled in delivering circadian lighting performance, assessed through metrics that evaluate the alignment of artificial lighting with biological needs:
- Melanopic Equivalent Daylight Illuminance (EDI): Maintained efficiency within 10% of natural daylight across correlated color temperature (CCT) ranges from 4,277 K to 22,333 K.
- Circadian Stimulus (CS) and Circadian Lighting (CLA): Demonstrated improved values over commercial RGBA and phosphor-converted LEDs (pc-LEDs), ensuring minimal disruption to circadian rhythms.
This performance positions TADF-WLEDs as a superior choice for human-centric applications where circadian health is a priority.
- Spectral Tunability Across Conditions
The TADF-WLED system showed exceptional tunability, simulating SPDs of diverse lighting conditions, including:
- Clear morning daylight
- Midday sunlight
- Sunset lighting
- Overcast skies
This capability allows users to customize lighting for specific environments or times of day, mimicking natural light transitions.
- Energy Efficiency and Sustainability
The system capitalized on the high wall-plug efficiency of violet-emitting LEDs (VLEDs), achieving theoretical power efficacies exceeding 390 lumens per watt. Additionally:
- Sustainability: The use of additive manufacturing and TADF dyes reduces the environmental footprint by eliminating rare-earth elements and enabling low-temperature processing.
These advantages highlight a step forward in balancing energy efficiency with high-quality lighting performance.
Compared to commercially available white LEDs, the TADF-WLED outperformed in both visual and non-visual (circadian) metrics. Additionally, its additive manufacturing process and reliance on organic materials reduce the environmental footprint, addressing sustainability goals.
Possible Implications for Future Human-Centric Lighting
This research aims to set a new standard for electric lighting by overcoming the limitations of traditional LED systems. The ability to spectrally tune SPDs during operation marks a significant departure from conventional fixed-spectrum technologies. Applications of this technology span residential, commercial, and healthcare settings, where lighting can be adapted to support human well-being and productivity.
Moreover, the use of additive manufacturing introduces scalability and customization, enabling lighting systems tailored to specific environmental or architectural needs. The technology's compatibility with sustainable materials further enhances its potential to transform the lighting industry.
By achieving high performance in visual fidelity, circadian alignment, and energy efficiency while maintaining spectral tunability and sustainability, the TADF-WLED represents a significant advancement in human-centric lighting technology.
Authors & Affiliations
- O. Moreno – Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, GA, USA
- C. Fuentes-Hernandez – Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, GA, USA
- B. Kippelen – Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, GA, USA
