Beyond red lies infrared
Moving along the spectrum beyond visible red to longer wavelengths takes us into infrared. It is not a deeper shade of red, but a band that our eyes cannot see directly.
In 1800, Herschel compared temperatures across split sunlight using thermometers and found warming beyond visible red. Read the story in NASA's introduction to infrared.
How does sunlight warm objects?
Solar radiation carries energy. When an object absorbs some incoming light, that energy can become internal thermal motion, raising its temperature. Objects also release energy to their surroundings, so actual temperature depends on materials, wind, and other environmental conditions.
Absorbed visible sunlight can also contribute to heating. NASA's explanation of Earth's energy budget distinguishes incoming solar radiation from outgoing thermal infrared radiation emitted by Earth; they should not be treated as the same spectrum.
Why do remote controls and thermal imaging both use infrared?
Some television remotes send signals using near-infrared light. Thermal imaging devices detect radiation in relevant infrared bands and turn it into visible images. These are different applications within the broad infrared spectrum.
The red, yellow, and blue in thermal images are usually display colours chosen to represent signal or temperature differences, not infrared colours seen directly by our eyes. When a device mentions infrared, consider the band it detects and its purpose.
What else matters in everyday assessments?
The US Department of Energy explains that solar radiation at the ground varies with location, time, season, terrain, and weather. Understand solar warming in its actual surroundings.
Feeling warmth does not replace UV information. For planning outdoor activities, read When outdoors, how should you consider sunlight and your surroundings?.
Distinguish warmth, comfort and an outing choice
List temperature, UVI and site conditions separately. A cool breeze does not guarantee low UV; lower UVI does not make heat suitable for activity. Check warnings, then choose practical shade, ventilation and rest.
If an afternoon stay in an open square meets a heat warning, change time or place. A storm warning is not resolved simply because the temperature drops. Adapt to conditions rather than score the day from warmth alone.
Thermal-image colours depend on scales and display settings. Check units, range and measured objects when comparing images. Apply the same habit to weather: identify the indicator, place and time before using it.