The colour of blood in water can appear green, particularly when red light is absent.
Why Does Blood Appear Green in Water?
The apparent colour of blood in water is not always the typical red we see on land. This shift in colour is due to how light interacts with both water and blood. Here's a breakdown:
- Red Light Absorption: The red colour of blood is due to the red wavelengths of light reflecting off the haemoglobin in the blood.
- Water Filtration: Water tends to absorb red light, especially as depth increases.
- Green Light Reflection: According to the reference, without the presence of red light, only green light reflects from the blood. This effect is noticeable when a diver gets a cut, as the blood appears green under the water. This green hue is not a change in the blood itself, but rather, the absence of the red light makes the inherent green reflection more visible.
Practical Insights
Diving
- Divers might be surprised when they get a cut underwater, as their blood will not appear red but rather green.
- This is not an indication of any change or problem with the blood itself; instead, it is a consequence of light refraction and absorption by the water.
Depth
- The deeper the water, the more red light is absorbed. As you descend, the green hue will become more pronounced, given the red component of white light diminishes further.
Summary
| Condition | Observed Colour | Explanation |
|---|---|---|
| On Land | Red | Red light is reflected from haemoglobin. |
| In Water (Shallow) | Reddish-Green | Some red light reflected but green becomes more visible as water filters out the red |
| In Water (Deep) | Green | Red light is absorbed by the water; green light reflection from the blood becomes dominant. |
