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Does blood glow under light?

Blood is a vital bodily fluid that transports oxygen and nutrients throughout the body. But does this red liquid produce any kind of glow when exposed to light? In this article, we’ll explore the science behind blood’s interaction with light and find out if blood really glows or not.

The Composition of Blood

To understand if and how blood glows, we first need to understand what it’s made of. Blood is composed of plasma, red blood cells, white blood cells, and platelets. Plasma makes up about 55% of total blood volume and is mostly water (92% by volume) with proteins, glucose, mineral ions, hormones, carbon dioxide, and blood cell fragments suspended within it. Red blood cells (erythrocytes) are specialized cells packed with hemoglobin, an iron-containing protein that binds oxygen and carbon dioxide for transport. White blood cells (leukocytes) are part of the immune system and defend the body against infection. Platelets (thrombocytes) are cell fragments involved in blood clotting.

The Role of Hemoglobin

Hemoglobin inside red blood cells plays a key role in determining if and how blood interacts with light. Hemoglobin contains heme groups with iron atoms that bind to oxygen, giving blood its red color. But does this pigmented biomolecule make blood glow?

Blood’s Interaction with Light

When normal blood is illuminated, it does not glow on its own. The red color comes from the large amount of hemoglobin absorbing blue and green light, leaving mostly red light to be reflected back. However, under certain conditions, blood can appear to “glow.” Here are some examples:


Some components in blood exhibit autofluorescence, meaning they re-emit absorbed light at a longer wavelength. For example, when illuminated with blue light, porphyrins in red blood cells give off a red fluorescence, while vitamin B2 (riboflavin) in plasma fluoresces green.


Blood can be made to luminesce through chemiluminescence – a process where chemical reactions produce light without heat. Adding luminescent reagents like luminol to blood catalyzes a chemiluminescent reaction that causes blood to visibly glow blue.


Phosphorescence occurs when certain substances absorb and re-emit light slowly over time. Blood proteins like albumin have phosphorescent properties. When dried blood is illuminated with strong blue light under darkened conditions, the albumin emits an eerie afterglow that can persist for several minutes after the light source is removed.

Photoluminescent Light Sticks

Glow sticks containing photoluminescent chemicals will make anything they touch appear to glow. Cracking open a glow stick and mixing its contents with blood can make the blood luminesce with the color of the light stick chemicals.

Real-World Examples

While blood does not normally glow, there are some real-world examples of blood fluorescence and luminescence:


Luminol chemiluminescence is used by forensic investigators to detect trace amounts of blood at crime scenes, causing it to glow blue in the dark.


Flow cytometry analyzes individual blood cells by fluorescence when suspended in fluid and passed through a laser beam.

Biomedical Research

Fluorescent tags are used to label and track blood cells and proteins in biomedical experiments.


Glow stick “blood” and fluorescent dyes are used to create ghoulish glowing “wounds” for Halloween.

The Glowing Blood Myth

Fiction sometimes depicts blood glowing red under dim light or moonlight without any enhancing substances added. For example, vampire mythology proposes that vampires can track victims by the glow of blood under the moon. However, blood does not contain any natural bioluminescent or photoluminescent chemicals that would make it glow on exposure to light without additions like luminol or phosphorescent tags. While clever special effects can make blood appear to emit a supernatural glow in movies, in real life blood does not glow under natural conditions.


In summary, while normal blood does not glow, it can be made to fluoresce or luminesce under certain conditions. Fluorescent dyes, chemiluminescent reagents, and photoluminescent chemicals introduced into blood can produce glowing effects. Some components of blood also exhibit natural fluorescent or phosphorescent properties that can cause a glow when illuminated by specific light sources. But under regular conditions, the hemoglobin in blood simply absorbs and reflects red light, without any emission of photons resulting in a glow.

Blood Component Glow Mechanism
Hemoglobin No glow – absorbs and reflects light
Porphyrins Autofluorescence when exposed to blue light
Riboflavin Autofluorescence when exposed to blue light
Albumin Phosphorescence when dried and exposed to blue light
Luminol Chemiluminescence when mixed with blood
Fluorescent dyes Fluorescence when exposed to light of specific wavelength
Photoluminescent chemicals Glows when exposed to light

So while blood alone doesn’t glow, with the right activates and conditions, it can be made to visibly luminesce or fluoresce. This unusual property has found uses in fields like medical diagnostics and biomedical research, as well as creating visually stunning special effects for film and theater. But vampire hunters hoping to track the undead by moonlight will unfortunately find that human blood by itself fails to provide any supernatural glow.