Final answer:
Cones are the photoreceptors that require a higher level of light energy for activation, functioning primarily in bright light conditions unlike the more sensitive rods which are used for low light vision.
Step-by-step explanation:
The photoreceptors that require a higher level of light energy for activation are the cones. Unlike rods, which are very sensitive and can be activated by low levels of light, cones need brighter light conditions to function. The human retina contains two types of photoreceptors: rods and cones. Rods dominate vision under low light levels and are about 1000 times more sensitive than cones. They do not mediate color vision, which is why we mostly see in shades of gray in the dark. In well-lit conditions, such as daylight, cones provide high-resolution color vision.
Each type of these photoreceptors has a different photosensitive pigment with distinct peak sensitivities. The three types of cones have peak sensitivities corresponding to the primary colors red, green, and blue, while rods contain the pigment rhodopsin, which is most sensitive to light at a wavelength of 498 nm. In normal sunlight, cones are active as rhodopsin in rods is bleached, meaning rods are nonfunctional in bright light and thus cones require more light energy to be activated.