Cincinnati Children's Blog

Who Turned Out the Lights?

Who Turned Out the Lights?

Have you ever wondered why it’s so dark in an ultrasound scan room? Many patients question why we turn the lights down when they come in for a scan. The answer is simple: so we can see better!

The retina in the human eye contains two types of photoreceptor cells: the cones and the rods. There are approximately 6 million cone cells and they are responsible for detecting color. Scientists estimate the human eye can detect around 10 million unique colors!


The rod cells are more numerous and more sensitive than the cones. Scientific literature reports the human retina contains roughly 120 million rod cells and can see around 30 shades of gray. These rod cells cannot perceive color, but instead are excellent at distinguishing the size, shape and brightness of images.


The number of shades of gray we can perceive is greatly affected by the lighting conditions and the background color. It can be difficult to identify many shades of gray on modern computer monitors. Decreasing the light in our scanning and reading rooms helps the sonographers and radiologists to visualize the various shades of gray more clearly. This clearer picture aids in diagnoses and ultimately can change the outcome for our patients.

Write a Comment

No Comments Yet