Working in Wavelengths
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Figure 1: Visualization of the electromagnetic spectrum, quantified using wavelengths, with the visible region highlighted
Any portion of the electromagnetic spectrum is qualitatively defined by the wavelength of light that comprises it. In other words, the wavelength of a light wave tells us almost everything we would want to know about it. In fluorescence microscopy, the nanometer (nm) is the most commonly used unit and the portion of the spectrum that is typically reported as perceptible by humans ranges from about 380nm to 710nm. Although individual subjectivity makes it difficult to quantify, only about 15% of humans can see anything above 680nm, and it is not recommended to view light below 420nm due to the risk of eye damage. The visible spectrum can be broken up into particular ranges of wavelengths; each corresponding to what we call colors:
- violet and indigo: 380 - 450 nm
- blue and aqua: 450 - 500 nm
- green: 500 - 570 nm
- yellow and orange: 570 - 610 nm
- red: 610 - 710 nm
The wavelengths that direcly flank the visible spectrum are also useful to the world of fluorescence. They are comprised of the short-wavelength band from 320 to 400 nm (near-UV) and the long-wavelength band from 750 to approximately 2500 nm (near-IR).
In optics, wavelength is often chosen over frequency to quantify light, but they are both proportional and either is accurate. Wavelength (and therefore frequency) is also directly proportional to a wave’s energy, as originally described by Max Planck with the following equation:
- E = hc/λ
Where E is energy, h is Planck’s constant, c is the speed of light, and λ is the wavelength of light. This relationship expresses the idea that light of a shorter wavelength (i.e. violet) has more energy than light of a longer wavelength (i.e. red).