How do plants in the Deep ocean survive with little or no sunlight

As we know the sunlight can hardly reach deep sea floor so the question arises how do deep sea plants survive with no sunlight.

This place seems impossible for sustaining life but some plants and animals still survive in those conditions where the pressure is high and temperature is very low.

One of the plants that survive deep in the oven is a red algae now the question is , how does red algae get sunlight for photosynthesis.

Red algae appear red because they contain pigment called phycoerythrins.
This pigment appears red because it reflects the red light and can absorb blue light.

Sunlight contains many colours and when these colours gets combine white light is produced , visible spectrum has many colours like orange yellow green blue and violet.

If we compare red and blue light , red light has longest wavelength where as blue light has shortest wavelength compared to red light so when wavelength decreases energy increases and when wavelength increases energy decreases.

Therefore red light is not able to penetrate deeper in the Ocean whereas blue light can penetrate deeper in the ocean because it has lowest wavelength and more energy then red light.

This helps are red algae survive with very low light, deep in the ocean.