Yes, light does stop penetrating through water as we go deeper. The ability of light to penetrate through water depends on its wavelength and the properties of water itself. The phenomenon of light attenuation, or the gradual reduction in the intensity of light as it travels through a medium, is responsible for this.
Water is not a completely transparent medium. It contains various molecules, suspended particles, and dissolved substances that can absorb and scatter light. As light passes through water, it interacts with these components, causing its intensity to decrease. The process of absorption occurs when certain molecules in water absorb light energy, converting it into other forms of energy (such as heat) and reducing the light's intensity. Scattering, on the other hand, happens when light interacts with particles or molecules smaller than its wavelength, causing it to change direction.
As we go deeper into the water, more and more light is absorbed and scattered, leading to a decrease in its intensity. Different wavelengths of light are absorbed to varying degrees by water, with longer wavelengths (such as red and infrared) being absorbed more readily than shorter wavelengths (such as blue and green). This is why, as we descend deeper into water, the colors that are absorbed first are the warmer colors like red, orange, and yellow, leaving behind the cooler colors like blue and green.
At a certain depth, known as the euphotic or photic zone, the intensity of light becomes too weak for photosynthesis to occur. This depth can vary depending on factors like water clarity, suspended particles, and the presence of dissolved substances. In very clear oceanic waters, the euphotic zone can extend to depths of around 200 meters (660 feet). In more turbid or polluted waters, it may be significantly shallower.
Below the euphotic zone, light is essentially absent, and this region is referred to as the aphotic zone. In the aphotic zone, no sunlight penetrates, and organisms rely on other sources of energy, such as chemosynthesis (utilizing chemical energy) or detritus from above.
It's important to note that the depth at which light stops penetrating through water can vary depending on the specific conditions of the water body.