Ambient light could power wearables for round-the-clock health monitoring, according to researchers at the Korea Advanced Institute of Science & Technology (Kaist).

Miniaturisation and weight reduction of medical wearable devices for continuous health monitoring such as heart rate, blood oxygen saturation and sweat analysis remain major challenges. In particular, optical sensors consume a significant amount of power for LED operation and wireless transmission, requiring heavy and bulky batteries.

To overcome these limitations, Kaist (www.kaist.ac.kr) researchers have developed a wearable platform that enables 24-hour continuous measurement by using ambient light as an energy source and optimising power management according to the environment.

Professor Kyeongha Kwon’s team from the School of Electrical Engineering, working with Chanho Park’s team at Northwestern University (www.northwestern.edu) in the USA, developed an adaptive wireless wearable platform that reduces battery load by using ambient light. It integrates three complementary light energy technologies.

The first core technology, the photometric method, is a technique that adaptively adjusts LED brightness depending on the intensity of the ambient light source. It automatically dims the LED when natural light is strong and brightens it when natural light is weak. Conventional sensors keep the LED at a fixed brightness regardless of the environment. This technology optimises LED power in real time according to the surrounding environment. Experimental results showed that it reduced power consumption by as much as 86.2% under sufficient lighting conditions.

The second is the photovoltaic method, using high-efficiency multijunction solar cells. This goes beyond simple solar power generation to convert light in indoor and outdoor environments into electricity. In particular, the adaptive power management system automatically switches among 11 power configurations based on ambient conditions and battery status to achieve optimal energy efficiency.

The third technology is the photoluminescent method. By mixing strontium aluminate microparticles into the sensor’s silicone encapsulation structure, light from the surroundings is absorbed and stored during the day and slowly released in the dark. As a result, after being exposed to 500W/m² of sunlight for ten minutes, continuous measurement is possible for 2.5 minutes even in complete darkness.

Strontium aluminate microparticles are a photoluminescent material used in glow-in-the-dark paint or safety signs, absorbing light and emitting it in the dark for an extended time.

These three technologies complement each other; during bright conditions, the first and second methods are active, and in dark conditions, the third method provides additional support, enabling 24-hour continuous operation.

The research team applied this platform to various medical sensors to verify its practicality. The photoplethysmography sensor monitors heart rate and blood oxygen saturation in real time, allowing early detection of cardiovascular diseases. The blue light dosimeter accurately measures blue light, which causes skin aging and damage, and provides personalised skin protection guidance. The sweat analysis sensor uses microfluidic technology to simultaneously analyse salt, glucose and pH in sweat, enabling real-time detection of dehydration and electrolyte imbalances.

Additionally, introducing in-sensor data computing significantly reduced wireless communication power consumption. Previously, all raw data had to be transmitted externally, but now only the necessary results are calculated and transmitted within the sensor, reducing data transmission requirements from 400byte/s to 4byte/s.

To validate performance, the research tested the device on healthy adult subjects in four different environments: bright indoor lighting, dim lighting, infra-red lighting and complete darkness. The results showed measurement accuracy equivalent to that of commercial medical devices in all conditions. A mouse model experiment confirmed accurate blood oxygen saturation measurement in hypoxic conditions.

“This technology will enable 24-hour continuous health monitoring, shifting the medical paradigm from treatment-centred to prevention-centred,” said Kwon. “Cost savings through early diagnosis as well as strengthened technological competitiveness in the next-generation wearable healthcare market are anticipated.”

This research (www.nature.com/articles/s41467-025-60911-1) was published last month in the international journal Nature Communications, with Do Yun Park, a doctoral student in the AI semiconductor graduate programme, as co-first author.