What is the difference between a reflex and other actions in the body

A reflex is involuntary however, other actions are voluntary in nature

A reflex action is an involuntary and almost instantaneous movement  in response to a stimulus. It usually does not require any thought or input and therefore does not directly involve the brain.

The path taken  by the nerve impulses in a reflex action is called a reflex arc. Most reflex arcs involve three neurons. There are two types of reflex arcs namely autonomic reflex arc which involves the inner organs of the body, and somatic reflex arc, which involves muscles.

measuring light intensity

light meters can be used to measure light intensity. the meter is held at the soil surface and pointed in the direction of the maximum light intensity, and then the meter is read.

errors can be made when measuring light intensity by accidentally shading the light meter. the reliability of the results can be checked by taking many samples.