What's the difference between a red light and a purple light?

In the same medium, the refractive index of violet light is greater than that of red light.

2. Wavelength

The wavelength of red light is longer than that of violet light with the highest frequency, so it has the largest refractive index and the shortest wavelength.

3. Wave velocity

In a vacuum, all colors have the same speed; In the presence of a medium, different colors of light have different refractive indices. The fastest visible light in the air is red light with the lowest frequency, and the slowest is purple light.

4. Frequency

If the wavelength of red light is longer than that of purple light, the frequency of red light is lower than that of purple light, so the energy of red light photons is small.

Extended data

Physical source

Ultraviolet light is generated by the excitation of electrons in the outer layer of atoms. The main ultraviolet light source in nature is the sun. When sunlight passes through the atmosphere, ultraviolet rays with wavelength less than 290nm are absorbed by ozone in the atmosphere.

The artificial ultraviolet light source has arcs of various gases (such as low-pressure mercury arc and high-pressure mercury arc), and ultraviolet light can chemically make the photographic film sensitive and has a strong fluorescence effect. Fluorescent lamps, all kinds of fluorescent lamps and black lights used to trap and kill pests in agriculture, all use ultraviolet rays to excite fluorescent substances to emit light.

Ultraviolet rays can also prevent counterfeiting and have physiological functions such as sterilization, disinfection, and treatment of dermatosis and rickets. Ultraviolet rays have strong particle properties and can produce photoelectric effects on various metals.