Light
To detect means to perceive or become aware of something through one's senses or instruments. In this context, it refers to sensing or recognizing stimuli using visual receptors in the eye.
These are specialized structures that respond to specific stimuli (like light) and transmit signals to other parts of the nervous system.
Perception involves interpreting sensory information received from our environment based on our previous experiences and knowledge.
The threshold is the minimum amount of stimulus needed for a sensory system to detect or respond to it.