The word “circadian“, invented by Franz Halberg, comes from the Latin words that literally means “approximately one day.” A circadian rhythm is approximately-24-hour cycle in the physiological, biochemical, or behavioral processes of living things, including animals, plants, cyanobacteria and fungi. These processes consist of body temperature, sleep-wake cycles, release of hormones and blood pressure. Additionally, photoperiodism, the physiological reaction of living things to the length of day or night, is imperative to both animals and plants, and the circadian system have a significant role in the measurement and interpretation of day length.

The circadian cycle is controlled by a part of the brain known as the hypothalamus, which is the main center for establishing sleep patterns and integrating rhythmic information. A region of the hypothalamus called the suprachiasmatic nucleus (SCN) gets signals from the retina of the eye about light and dark.

Determining the human circadian rhythm
The classic stage indicators for computing the timing of a human circadian rhythm are:
1. Core body temperature
2. Melatonin secretion by the pineal gland

For temperature research, people must stay awake but quiet and semi-reclined close to night time while their temperatures of the rectal area are taken constantly. The average temperature of human adult is at its lowest at about 5 a.m., approx 2 hours prior to usual wake time, although the difference is big among normal chronotypes.

Melatonin is missing from the system or gradually low in daytime. It begins in dim light, at around 9 p.m during the summer months and earlier in the winter months and can be computed in the saliva or the blood. Its main metabolite can also be computed in urine first thing in the morning.

Circadian rhythm sleep disorder
People with this disorder are not able to sleep and wake at the times needed for normal work, education, and social activities. Circadian rhythm sleep disorder is a range of disorders to do with the sleep timing. It means that an individual is waking up far too early to begin their day or else being unable get up at the right time for daily schedule. Shift work and Jet lag are both known as extrinsic causes and delayed sleep phase syndrome (DSPS) and non-24 syndrome are intrinsic causes of circadian rhythm sleep disorder.

Light therapy- It’s the best treatment for circadian rhythm sleep disorder and is intended for resetting the biological clock to the right time of day so that the people wake up and function correctly at the proper time. There are various ways that the light is supplied to an individual such as full and bright range lamps, these should be used for a set period of time.