Photosynthetic organisms use a limited portion of the electromagnetic spectrum of light. this portion is called light and consists of wavelengths of light from about 400 to 740 nm.

Explanation:

The portion visible by the human eye of the electromagnetic spectrum is between 380 nm (violet-blue) and 780 nm (red), but we can approximate this range to 400nm to 740nm. Which means this part of the spectrum is located between ultraviolet light and infrared light.

Note the fact only part of the whole electromagnetic spectrum is visible to humans is because the receptors in our eyes are only sensitive to these wavelengths. That is why the visible light (also called the visible portion of the electromagnetic spectrum) is the portion we can see.

Therefore:

This portion is called visible light and consists of wavelengths of light from about 400 to 740 nm.

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