Feb
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. Within this spectrum are the wavelengths we classify as infrared, visible light, ultraviolet and beyond. Understanding this spectrum helps explain phenomena we encounter every day.
Infrared Light (700nm – 1mm)
Infrared wavelengths carry heat energy and allow night vision devices to see objects by the infrared radiation they emit. Your microwave oven operates at a frequency of 2.45 GHz (gigahertz), warming food via water molecule vibration from infrared rays. Thermal cameras use infrared to create images based on objects’ thermal signatures.
Visible Light Spectrum (380nm – 750nm)
The narrow band we can see represents just a sliver of the spectrum. Violet, blue and green light have shorter wavelengths, while orange, red and other colors have longer wavelengths within this range. Our vision exists due to evolution optimizing detection of wavelengths useful for tasks like finding food sources.
colors visible to the human eye and their typical wavelength ranges:
Colors of the Visible Spectrum:
Within the overall 380-750nm range of visible light, the human eye can perceive different colors corresponding to specific wavelength bands:
- Violet: 380-450nm
- Blue: 450-495nm
- Green: 495-570nm
- Yellow: 570-590nm
- Orange: 590-620nm
- Red: 620-750nm
The shortest wavelengths appear violet/blue, with greens, yellows, and oranges in the middle range. The longest visible wavelengths appear as shades of red.
It’s important to note that the boundaries between colors are not strictly defined. Where one color ends and another begins depends on factors like intensity of the light. Also, some people may perceive slightly different breakdowns depending on variations in individual color vision.
The colors we see emerge from the overlapping responses of three types of photoreceptor cone cells in the retina – sensitive to long, medium, and short wavelengths respectively. Different combinations of firing in these three cell types convey the perception of particular colors to the brain.
This allows the human eye to distinguish the primary visible colors as well as a diverse array falling between the main spectral hues. Variations in wavelength, even as small as 10nm, can be differentiated as distinct color shades.
RGB display system
In the RGB (red, green, blue) color system used in displays, pure red, green and blue lights can each be produced. But there is no single wavelength for other hues like purple or cyan, which are mixed:
- Purple is produced by combining red and blue lights, to substitute for the missing violet/blue wavelengths between blue and red.
- Cyan is produced by combining green and blue, in place of the wavelength ranges between blue and green not directly producible.
Other hues like yellow appear because our eyes mix red and green lights additively. Magenta is a result of red and blue lights mixing subtractively to simulate the missing violet wavelength our eyes expect between them.
So while the visible spectrum is a continuum, RGB displays produce in-between colors through color theory principles of additive and subtractive mixing, to mimic the apparent hues associated with wavelengths our eyes are sensitive to detecting.
- Individual pixels on an RGB display cannot produce the color yellow directly.
- A yellow appearance is produced by having both red and green pixels illuminated at the same spatial location.
- The eye and brain combine the red and green light from those pixels additively, perceiving the mixture as yellow.
- So you are correct that from a pixel-level perspective, the locations cannot genuinely be yellow – they must be activating both red and green subpixels simultaneously to create the yellow perception.
Ultraviolet Light (10nm – 380nm)
Just outside of visible light, UV radiation is still high energy enough to cause chemical reactions. Dermatologists use UV light therapy to treat skin conditions, tanning beds emit UVA and UVB rays, and forensic analysts employ UV lamps to view evidence not normally visible to the naked eye.
X-rays (0.01nm – 10nm)
Discovered by Wilhelm Röntgen in 1895, x-rays have wavelengths so short they can pass through human tissue, allowing medical scanning technologies. Airports use x-ray machines to screen carry-on luggage without opening bags. Their ability to penetrate matter makes x-rays invaluable tools in hospitals and security.
From microwaves enabling wireless devices to gamma rays powering nuclear reactions, the full electromagnetic spectrum underlies modern technologies while invisible light illuminates unseen processes in our natural world. Continued exploration advances science and its applications across industries.
Difference between “infra” and “ultra” wavelengths frequencies
The terms “infrared” and “ultraviolet” refer to wavelengths just outside the visible light spectrum. Here’s an explanation of why they are labeled “infra” and “ultra”:
- Infrared means “below red” – it refers to wavelengths longer (lower frequency, higher value) than visible red light, but still shorter than microwave wavelengths.
- Red light is at the long wavelength/low frequency end of the visible spectrum, around 620-750nm. Infrared immediately follows after.
- So infrared captures wavelengths “below” or “beyond” the reds that we can see, ranging from around 750nm to 1mm.
- Ultraviolet means “beyond violet” – it refers to wavelengths shorter (higher frequency, lower value) than visible violet/blue light, but still longer than X-rays.
- Violet/blue light is at the short wavelength/high frequency end of the visible spectrum, around 380-450nm. Ultraviolet immediately precedes this.
- So ultraviolet captures wavelengths even “closer” or “beyond” the violets/blues at the high frequency limit of human vision, ranging from about 10nm to 380nm.
In essence, “infra” labels longer, lower frequency wavelengths beyond red light, while “ultra” labels shorter, higher frequency wavelengths closer to/beyond violet light. The terms indicate their position relative to the boundaries of the visible spectrum.
Drilling a little bit more in colors combination wavelengths
Visible Light Spectrum Colors
| Wavelength | Color | Value | Category |
|---|---|---|---|
| 380-450 | Violet/Blue | 380 | Hue |
| 450-495 | Blue | 450 | Hue |
| 495-570 | Green | 500 | Hue |
| 570-590 | Yellow | 560 | Hue |
| 590-620 | Orange | 580 | Hue |
| 620-750 | Red | 630 | Hue |
540|(Purple)|Red(630) + Blue(450) / 2|Combination
475|(Cyan)|Green(500) + Blue(450) / 2|Combination
540|(Magenta)|Red(630) + Blue(450) / 2|Combination
635|(Pink)|Red(630)+White(Red+Green+Blue)/2|Combination
530|(Lime)|Green(500) + Yellow(560) / 2|Other
475|(Aqua)|Blue(450) + Green(500) / 2|Other
570|(Amber)|Orange(580) + Yellow(560) / 2|Other
630|(Crimson)|Red(630) + Magenta(540) / 2|Other
630|(Violet-Red)|Red(630) + Violet/Blue(380) / 2|Other
-|(White)|Red(630)+Green(500)+Blue(450)|Combination
560|(Brown)|Orange(580)+Green(500) / 2|Other
-|(Gray)|Black(0)+White(Red+Green+Blue)|Combination
What about color on plastic for example?
We’ve been focusing only on the visible light spectrum colors, but colors we perceive can be influenced by other factors beyond just wavelength. Orange plastic is a great example of this.
While orange appears as a spectral color ranging from 590-620 nm, the orange we see in plastic is not produced by a single wavelength. Plastic pigments work through subtractive color mixing – they absorb certain wavelengths and reflect others.
Common organic pigments used to make plastic appear orange include:
- Diarylide yellow (DY-10) – Absorbs blue wavelengths, reflecting yellow and red to produce the orange hue.
- Diazotized benzidine (DB-16) – Absorbs blue-green and transmits yellow, red and orange wavelengths.
So in plastics and other colorants, orange can be produced through subtractive color mixing even if it’s not a precise wavelength range.
Different types of electromagnetic radiation fall within the full electromagnetic spectrum
- Gamma Rays – Shortest wavelengths, very high frequency. Used in things like gamma ray bursts, nuclear medicine imaging.
- X-Rays – Slightly longer than gamma rays but still high frequency. Used in medical imaging and security screening.
- Ultraviolet – UV rays have wavelengths longer than x-rays but shorter than visible light. Used in things like tanning beds but also causes sunburns.
- Visible Light – The range we can see, from violet to red light wavelengths. Important for vision and photography.
- Infrared – Longer wavelengths than visible light but shorter than microwaves. Used in night vision, thermal imaging, remote controls.
- Microwaves – Even longer wavelengths used in things like cell phones, WiFi, microwave ovens.
- Radio Waves – The longest wavelength electromagnetic waves, used for communications like radio, television broadcast, walkie talkies.
So in summary – gamma to UV is higher frequency/shorter wavelengths, visible light is in the middle, and infrared to radio is lower frequency/longest wavelengths.
Infrared and ultraviolet border visible light but are just outside what our eyes can detect naturally. All of these types of electromagnetic radiation demonstrate the different wavelengths that make up the full electromagnetic spectrum.
The ability to produce heat via electromagnetic radiation is based on wavelength/frequency, not the specific type of radiation. In theory, any EM waves with wavelengths shorter than infrared could generate heat through excitation of molecules.
- Microwaves produce heat because their short wavelengths/high frequencies excite molecular motion.
- The same heating effect could be achieved with any EM radiation that has even shorter wavelengths:
- Ultraviolet radiation has shorter wavelengths than microwaves, so UV waves would deposit energy into a material even more efficiently, rapidly generating heat.
- X-rays and gamma rays have much higher frequencies than UV due to their extremely short wavelengths – they would heat materials very quickly through dielectric/molecular excitation.
- Visible light wavelengths could also produce heating, just not as rapidly as higher frequency radiation like UV, X-rays or gamma rays.
So in general terms, anything on the electromagnetic spectrum with wavelengths shorter than infrared (i.e. higher frequency waves) has the potential to directly generate heat in a material via interaction/energy transfer at the molecular level. It’s not unique to microwaves – it’s a wavelength-dependent phenomenon.
