Question

What is the wavelength range, in \(\mu \mathrm{m}\), for infrared light? In what portion of this range does the Earth receive IR from the Sun? What are the wavelength limits for the thermal IR range?

Short answer

Infrared light spans 0.7–100 μm. Earth receives IR from around 0.7–5 μm. Thermal IR is 3–30 μm.

Step-by-step solution

Understanding Infrared Light

Infrared (IR) light is part of the electromagnetic spectrum and sits just beyond the visible light range, extending to microwave wavelengths. The IR range typically spans from 0.7 1m to 100 1m.

IR Range from the Sun

The majority of the IR radiation received from the sun falls within the near-infrared range, which is approximately from 0.7 1m to around 5 1m. This is the range where the sun emits most of its infrared energy.

Thermal Infrared Range

The thermal infrared range is usually defined as spanning from about 3 1m to 30 1m. This is the range that corresponds to the heat emitted by objects at temperatures encountered in Earth's environment.

Key concepts

Electromagnetic Spectrum

The electromagnetic spectrum is a vast and diverse range of all types of electromagnetic radiation. Electromagnetic radiation includes energy waves like light, which have electric and magnetic fields vibrating at right angles to each other.
All types of electromagnetic radiation are grouped by their wavelength and frequency, forming the electromagnetic spectrum.
This spectrum includes:

• Radio waves
• Microwaves
• Infrared light
• Visible light
• Ultraviolet light
• X-rays
• Gamma rays

Wavelength is the distance between consecutive crests of a wave, and it varies across the spectrum. The spectrum orders these wave types from longest wavelength to shortest. Infrared light falls just beyond the red part of visible light and continues into the microwave region.

Near-Infrared Range

Near-infrared is the part of the infrared spectrum that falls just after visible light, specifically in the 0.7 to about 5 micrometers (\(\mu \mathrm{m}\)) range.
This range is often where we get a lot of infrared energy from the sun.
The near-infrared range is important for several technologies and applications:

• Astronomy: Allows us to study dust clouds in space.
• Remote sensing: Used in satellite imaging for vegetation and water content analysis.
• Thermal efficiency: Helps in solar cell design to harness energy more effectively.

While the human eye cannot see near-infrared light, it can be detected using special sensors and cameras.

Thermal Infrared Range

The thermal infrared range is where most of the infrared energy associated with heat is found.
It comprehensively spans from approximately 3 to 30 micrometers (\(\mu \mathrm{m}\)).
Infrared in this range is primarily associated with thermal or heat radiation from objects.
Everyday objects and bodies that emit heat do so in thermal infrared range.
This range is critical for:

• Thermal Imaging: Used in cameras to detect heat differences in objects.
• Weather Satellites: Helps in monitoring Earth's surface temperatures.
• Environmental Monitoring: Assists in studying greenhouse gas emissions and energy loss.

Thermal infrared radiation is useful for seeing temperature distributions without direct contact with the object.

Wavelength of Light

The wavelength of a wave is a unique distance between two successive crests or troughs in a wave sequence.
In light waves, this distance determines color—shorter wavelengths correspond to blue tones, while longer wavelengths appear red.
Infrared light contains longer wavelengths compared to visible light, typically measured in micrometers (\(\mu \mathrm{m}\)).
Wavelength is critical to understanding and distinguishing between different types of electromagnetic radiation. Knowing the wavelength helps identify the part of the electromagnetic spectrum where light belongs. From measurements in wavelengths:

• The visible light spectrum spans roughly 400 to 700 nanometers.
• Infrared light ranges from 0.7 to 100 micrometers.

Different technologies use these characteristics for various applications like lighting, medical scans, and scientific studies.

Infrared Radiation from Sun

The Sun emits a broad range of energy across the electromagnetic spectrum, including a significant amount of infrared radiation.
Most infrared radiation that reaches Earth from the Sun falls into the near-infrared range, between 0.7 and 5 micrometers (\(\mu \mathrm{m}\)).
This portion contains about half of the solar energy the Earth receives.Infrared radiation from the Sun plays a vital role in maintaining the Earth's thermal balance. This energy warms our atmosphere and the planet's surface, driving weather patterns and contributing to the greenhouse effect.

• Solar Power: Near-infrared is harnessed in solar panels for energy.
• Climate Observations: Helps in understanding energy distribution and climate effects.
• Atmospheric Studies: Key component in studying radiation absorption and emission in Earth's atmosphere.

Understanding how infrared radiation from the Sun interacts with Earth is essential for climate science and energy management.