When a person moves from bright sunlight into a dark room, the inability to see immediately is primarily due to the time taken by the visual system to adapt to low light, called dark adaptation. This phenomenon is strongly linked to the behavior of the photopigment rhodopsin in rod cells.

Rhodopsin and Light Inactivation

• Rhodopsin, the visual pigment in rod photoreceptor cells, is responsible for night (scotopic) vision.

• In bright light, rhodopsin undergoes photoisomerization and is converted to an inactive form called metarhodopsin II (Meta II).

• This activated rhodopsin triggers the phototransduction cascade, but after activation, it is phosphorylated and bound by arrestin, leading to inactivation.

• The pigment then slowly decays and must be regenerated by recombining with 11-cis retinal in a process known as the visual cycle.

• Until rhodopsin regenerates, rods are less sensitive, causing temporary blindness or inability to see in the dark.pmc.ncbi.nlm.nih+2

Why Vision Is Impaired in Dark Rooms

• After leaving bright light, the rods have depleted active rhodopsin and cannot respond efficiently to low light.

• The delay in rhodopsin regeneration causes the transient blindness period lasting seconds to minutes.

• This process is called dark adaptation.

Evaluating The Choices

• (1) Rhodopsin pigment is light inactivated: Correct. Light causes rhodopsin to become inactive and necessitates regeneration.

• (2) Scotopsin proteins are denatured: Incorrect. Scotopsin (the protein part of rhodopsin) is not denatured but reversibly inactivated.

• (3) All rhodopsin are bound with protein: Incorrect and vague.

• (4) All scotopsin becomes non-functional: Incorrect; only light-activated rhodopsin temporarily loses function.

Conclusion

Temporary inability to see in the dark after exposure to bright light is due to light inactivation of rhodopsin pigment and the time required for its regeneration.

The correct answer is:

(1) Rhodopsin pigment is light inactivated