The visible spectrum is the portion of the electromagnetic spectrum that the human eye can perceive, corresponding to wavelengths between approximately 380 nm (violet) and 780 nm (red). White light contains all these wavelengths mixed together.
Discover FizziQ
How to measure it in class
With the FizziQ app, the colorimeter allows you to analyze the colored components of light.
Steps:
- Open FizziQ and select the “Colorimeter” instrument
- Analyze different light sources (sun, lamp, screen)
- Observe the R, G, B components of each light
- Use a prism or diffraction grating in front of the camera to disperse the light
- Identify the spectral lines of a vapor lamp
Scientific activities on this topic
- Analysis of sunlight: https://www.fizziq.org/en/activities/additive-color-mixing-rgb/
- Comparison of LED, incandescent, and fluorescent light
- Study of absorption and emission lines
Learn more
The colors of the spectrum:
| Color | Wavelength (nm) | Frequency (THz) |
|---|---|---|
| Violet | 380-450 | 670-790 |
| Blue | 450-495 | 605-670 |
| Green | 495-570 | 525-605 |
| Yellow | 570-590 | 510-525 |
| Orange | 590-620 | 485-510 |
| Red | 620-780 | 385-485 |
Beyond the visible:
- Ultraviolet (wavelength < 380 nm): tanning, disinfection, bee vision
- Infrared (wavelength > 780 nm): heat, remote controls, night vision
Color perception:
The eye has three types of cones sensitive to blue (420 nm), green (530 nm), and red (560 nm). All perceived colors result from the combination of signals from these three types of receptors.
Formula
Relationship between wavelength and frequency:
c = lambda x f
where:
- c: speed of light (3 x 10^8 m/s)
- lambda: wavelength (m)
- f: frequency (Hz)
Energy of a photon: E = h x f = h x c / lambda
where h = 6.63 x 10^-34 J.s (Planck’s constant)
Application examples
- A rainbow disperses white light into its spectral components
- Screens use only R, G, B to recreate all colors
- White LEDs combine several colors or use phosphors
- Lasers emit a single wavelength (monochromatic light)
FAQ
Q: Why is the sky blue? A: Rayleigh scattering disperses short wavelengths (blue) more than long ones (red). Blue is scattered in all directions, coloring the sky.
Q: Does the FizziQ colorimeter measure wavelengths? A: No, it measures the R, G, B components received by the camera sensor. To measure wavelengths, a spectrometer would be needed.
Q: Why can’t we see infrared? A: Our cones are not sensitive to these wavelengths. Some animals (snakes) or devices (thermal cameras) can detect them.
Q: How many colors can we distinguish? A: The human eye can distinguish approximately 10 million different color shades.
Related concepts
Light - Wavelength - Frequency - Additive synthesis - Dispersion - Colorimeter - Spectroscopy