Phosphor-free white LED lamp rich in yellow-green spectrum

Semiconductor lighting technology is developing rapidly. While seeking high luminous efficiency, low cost, and superior reliability, researchers are increasingly focusing on the effects of LED products on health. Health-oriented optical technology is becoming a key development direction in semiconductor lighting.

 

Although researchers have reported on the photo-biological effects of blue and red spectra in LED, there have been few studies on the impact of yellow-green spectrum in LED on human health. This gap primarily results from the imbalance in the development of multi-color LED efficiency—yellow-green LEDs exhibited significantly lower luminous efficacy compared to LEDs in other colors. Therefore, high-efficiency yellow-green light has predominantly relied on phosphors.

 

However, phosphor-based lighting suffers from various limitations, including wide spectrum, inconvenient spectral regulation, thermal loss, and luminance degradation. These drawbacks hinder the development of LEDs in applications requiring high-quality illumination.

 

In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Jianqi Cai from Laboratory of Visual Health and Safety Protection, China National Institute of Standardization, and Professor Guangxu Wang from National Institute of LED on Si Substrate, Nanchang University, the authors have developed a phosphor-free LED lamp rich in yellow-green spectrum based on the high-efficiency yellow-light LED technology. Further, they explored the photo-biological effects of three lamps with distinct spectral characteristics: a phosphor-free LED lamp rich in yellow-green spectrum, a conventional LED lamp, and a full-spectrum LED lamp, evaluating their impacts on ocular function, brain activity, and circadian rhythm. The findings demonstrate that human visual performance and circadian rhythm are significantly enhanced under illumination from the phosphor-free LED lamp rich in yellow-green spectrum.

 

There are several key innovations in this study: (1) Developing the spectrum-tunable phosphor-free LED lamp based on the high-efficiency yellow LED technology, and exploiting a novel direction of health-oriented phosphor-free lighting; (2) In accordance with the testing methodology specified in the standard GB/T 44441-2024 "Test for Visual Health Comfort of LED Lighting Products", this study objectively quantified the impact of phosphor-free LED lamp rich in yellow-green spectrum on human visual function through multidimensional assessments including dynamic monitoring of ocular accommodation capacity, contrast sensitivity characteristics, and optical quality metrics, and demonstrated that spectral energy modulation in the yellow-green spectrum effectively enhanced visual comfort while reducing ocular functional load by integrating these physiological parameters with the Visual Comfort (VICO) model; (3) By investigating functional connectivity between distinct loci in the visual cortex under illumination with different spectral characteristics, this study characterized the positive effects of the phosphor-free LED lamp rich in yellow-green spectrum on the visual cortex, preliminarily revealing the unique influence of yellow-green spectrum on fine visual perception in the cortex, including color discrimination, shape recognition, and texture analysis; (4) Through measurements of salivary melatonin levels at different time points, this study objectively quantified the differential non-visual effects between the phosphor-free LED lamp rich in yellow-green spectrum and the two other LED lamps.

 

“This study challenges the current paradigm of "full-spectrum equals healthy" by revealing the differential regulatory mechanisms of distinct spectral characteristics on both visual and non-visual responses through multi-dimensional photobiological investigations. We have established a preliminary dose-effect model correlating spectral parameters with biological effects, thereby advancing healthful lighting technology from empirical imitation to scientific quantification.”

 

“The yellow-green-rich phosphor-free LED technology developed in this study could be applied in various health-oriented lighting areas, including classroom illumination, residential lighting, office environments, and medical lighting systems. In the display technology area, the photo-biological effects of yellow-green spectrum discovered in this study will advance the development of next-generation displays, providing a technical pathway to achieve healthy display solutions that simultaneously satisfy wide color gamut requirements and human visual health protection.

 

This study fills a critical research gap in the knowledge of the photo-biological effects of yellow-green spectrum on humans, providing both theoretical foundations and technical support for the development and industrial applications of yellow-green LED device in semiconductor lighting, next-generation displays, and photo-medicine. Some achievements in this study have been successfully industrialized in the fields of health-oriented lighting and displays.”

---

---