All living beings emit a subtle light that fades after death

Light is often associated with life, whether through the warm glow of a campfire or the brilliance of the sun. Yet, there is another kind of light – one that is nearly imperceptible but ever-present in living organisms.

This subtle illumination, known as ultraweak photon emission (UPE), is not visible to the naked eye but is a natural byproduct of metabolic processes.

Researchers at the University of Calgary recently explored UPE in a study that delved into its biological significance. Unlike bioluminescence, which produces visible light, UPE emits extremely low-intensity light that falls within the spectral range of 200–1,000 nm.

This phenomenon is observed in a wide range of life forms, from bacteria and plants to animals and humans.

Lighting up in life and death

In mice, UPE might signal vitality. The researchers compared living and recently deceased mice, capturing UPE with high-sensitivity imaging equipment.

The living mice shone brighter, while the recently deceased emitted barely any light. Both groups were kept at the same temperature of 37°C (98.6°F), but the difference in UPE was unmistakable.

This faint light might not look like much, but it could indicate life’s internal rhythm. The study suggests that UPE isn’t just random; it might be tied to fundamental biological processes that continue as long as life does.

Plant responses: Light as a signal

Plants emit UPE too, but in them, it responds to stress. The researchers exposed plant tissues to temperature changes, injuries, and chemicals. Injured areas glowed more intensely, and the brightness increased after chemical treatments.

Why the extra light? When plants experience stress, they ramp up chemical reactions that produce reactive oxygen species (ROS). These molecules are like cellular alarm bells. In their rush to signal damage, they produce tiny sparks of light, visible only through advanced imaging.

Living cells flash bursts of light

Think of living organisms as busy chemical labs. Cells carry out countless reactions to sustain life, and some reactions generate ROS. These molecules play dual roles – they’re essential for cell signaling but can become harmful when levels spike.

During stress, ROS levels surge, and oxidative stress kicks in. This imbalance excites electrons, creating conditions for UPE. It’s not a glow in the dark – it’s a faint, silent burst of photons, unnoticed by the human eye.

Invisible light from living cells

Capturing UPE requires ultradark enclosures and specialized cameras. The researchers used Electron-Multiplying Charge-Coupled Device (EMCCD) cameras for plants and Charge-Coupled Device (CCD) cameras for mice. These devices can detect UPE in controlled, dark settings, minimizing background noise.

The images revealed more than just faint glows. They showed how UPE changes with temperature, stress, and injury. In mice, the light vanished after death. In plants, chemical treatments and injuries made specific regions flare up, marking them as sites of stress or damage.

A potential diagnostic tool

What if doctors could detect stress and disease just by measuring UPE? The study hints that UPE could serve as a non-invasive diagnostic tool.

In mice, the difference between life and death appeared in the intensity of UPE. In plants, stress-induced light bursts pinpointed areas of damage.

If scientists can decode UPE patterns, they might develop ways to detect diseases earlier. Monitoring UPE could reveal cellular stress before symptoms become obvious, offering a glimpse into the body’s hidden struggles.

Light emissions and life processes

UPE blurs the line between physics and biology. It’s not just a quirk of cellular chemistry; it’s a signal, a pulse, a silent language of life.

The researchers suggest that understanding UPE could open doors to new diagnostic techniques and research avenues.

But much remains unknown. Why do some stressed cells emit more light than others? How do specific injuries alter UPE patterns? And could UPE one day serve as a life indicator, a subtle sign of biological activity in tissues?

The secrets of invisible light

The study from the University of Calgary raises more questions than it answers.

What exactly triggers UPE in stressed plants? How does cellular metabolism fuel these faint flashes of light? And could these light signals one day serve as early warning signs of disease?

For now, UPE remains a silent, invisible light – a flicker of living cells that scientists are only beginning to understand. But as researchers dig deeper, they may find that even the faintest light reveals vital clues to what it means to be living.

The study is published in The Journal of Physical Chemistry Letters.

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