What are the functional similarities between rods and cones?

Hint: At low light levels (scotopic vision), rods are responsible for vision. Cones are active at higher light levels (photopic vision) and are capable of colour vision along with being responsible for high spatial acuity, whereas Rods do not mediate colour vision and have low spatial acuity.

Complete answer: The rods and cones are known as photoreceptor cells. The working of the cones provides daylight or photopic vision and colour vision and the operation of the rods provides twilight or scotopic vision. The rods have a purple-red protein called visual purple or rhodopsin. It is produced by a vitamin A derivative, and thus this vitamin is essential for the proper functioning of the eyes. We have three types of cones in the human eye that have their own characteristic photopigments that react to red, green, and blue light colours. Various variations of these cones and their photopigments cause sensations of various colours. When these cones are stimulated equally, as white light has all colours in it a sensation of white light is created.
The following are some similarities between rods and cones:
1. They are both light-absorbing photoreceptors.
2. Both are located in the innermost layer of the retina of the eye.
3. Though the form and structure of pigments vary, they both contain photopigments.
4. Both are exteroceptors that are secondary.

Note: For colour vision, rods are not healthy. We primarily use our rods, as in a dark space, but we are "colour blind." In the periphery of the retina, rods are more numerous than cones. This is because the cones are used for colour vision and are more appropriate for fine information to be observed. The human retina comprises nearly 6 million cones.