Circadian Health Glossary

Irradiance

Irradiance measures the amount of electromagnetic radiation (light or other radiant energy) that reaches a specific surface area within a defined timeframe. This term quantifies the energy transmitted by light or radiation to a particular area over a certain period, serving as a critical parameter in understanding the "brightness" experienced by an individual or object exposed to light.

Key Elements Affecting Irradiance

Several factors converge to determine the irradiance levels a surface experiences:
  • Source– different sources of light emit different types of wavelengths. (e.g. lamp, sunlight).
  • Wavelength– different wavelengths carry different types of energy.
  • Direction– light is most potent when it hits a surface straight on.
  • Distance–irradiancedecreases the further the light source is from the subject.

Applications in Light Therapy and Chronobiology

Understanding irradiance is critical in two fields revolutionizing healthcare—light therapy and chronobiology.

Light Therapy

Light therapy, involves exposure to artificial light that mimics natural sunlight. It is used to treat several sleep-related conditions, including seasonal affective disorder (SAD), and different circadian rhythm sleep disorders. The efficacy of light therapy heavily relies on irradiance to tailor the intensity and duration of light exposure.

Chronobiology and Circadian Rhythms

Our internal body clocks are exquisitely fine-tuned to the day-night cycle, thanks in part to the light we receive. This interaction between light and our daily rhythms is the realm of chronobiology, which seeks to understand and optimize our interactions with light to promote wellness. Irradiance is a key metric in this quest to ascertain the ‘dose’ of light required to maintain or reset the circadian rhythm.

Related Definitions

Circadian Rhythm sleep Seasonal Affective Disorder (SAD) Chronobiology Irradiance CIRCADIAN HEALTH