Electromagnetic Spectrum


Optical radiation is a segment of the electromagnetic spectrum situated between X-rays and microwaves. It encompasses a range of wavelengths that play a significant role in biological reactions and various aspects of vision.

Subdivided into Seven Wavebands

Optical radiation is categorized into seven distinct wavebands, each with its unique characteristics and effects. These wavebands are as follows:

1. Ultraviolet C (UV-C): Ranging from 200 to 280 nm, UV-C consists of short wavelengths and high-energy photons. This portion is known for its potential to cause damage to biological tissues.

2. Ultraviolet B (UV-B): Extending from 280 to 315 nm, UV-B falls in the middle of the ultraviolet spectrum. It also carries potential risks to biological tissues.

3. Ultraviolet A (UV-A): Spanning from 315 to 400 nm, UV-A comprises longer wavelengths than UV-B and UV-C.

4. Visible Radiation: This waveband covers wavelengths from 400 to 780 nm, encompassing the colours of the visible spectrum. It is responsible for stimulating the retinal photoreceptors, enabling our sense of vision.

5. Infrared A (IRA): With wavelengths from 780 to 1400 nm, IRA contains near-infrared radiation. It can produce thermal effects on ocular structures.

6. Infrared B (IRB): Extending from 1400 to 3000 nm, IRB involves longer infrared wavelengths, which have specific interactions with ocular structures.

7. Infrared C (IRC): Covering the longest wavelengths in the optical radiation spectrum, ranging from 3000 to 10000 nm, IRC has unique characteristics and effects.

Wavelength and Energy Relationship

In the electromagnetic spectrum, the energy of individual quanta, or photons, of optical radiation is directly related to the wavelength. Shorter wavelengths correspond to greater energy, which is a fundamental principle to consider when evaluating the potential impact of optical radiation on biological tissues.

Interaction with Eye Components

Optical radiation interacts differently with various components of the eye. The cornea and sclera efficiently absorb short wavelengths in the ultraviolet range (UV-B and UV-C) and long wavelengths in the infrared range (IR-B and IR-C). UV-A is absorbed by the crystalline lens, whereas wavelengths between 400 and 1400 nm, including visible light and near-infrared, pass through the ocular media and reach the retina.

Sensory Perception and Thermal Effects

Visible wavelengths, falling within the 400 to 780 nm range, are responsible for stimulating the retinal photoreceptors, resulting in the perception of light. In contrast, near-infrared radiation, depending on its intensity and duration of exposure, may give rise to thermal effects within the eye.

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