Light purple is a color that combines pale tones of violet and pink. When we see light purple, what we are observing is visible light at wavelengths corresponding to that hue. But what does that mean in terms of energy? Visible light sits within a narrow band of the full electromagnetic spectrum, and different wavelengths of light carry different amounts of energy. By examining the relationship between wavelength, frequency, and energy, we can determine the energy level associated with light purple.
The Electromagnetic Spectrum
The full electromagnetic spectrum encompasses all electromagnetic radiation, from radio waves to gamma rays. The visible spectrum that humans can see is just a small slice, corresponding to wavelengths from approximately 380 to 750 nanometers. The visible spectrum can be broken down into the familiar sequence of colors – red, orange, yellow, green, blue, indigo, violet. As wavelength decreases, the corresponding color shifts from red to violet.
| Color | Wavelength (nm) |
|---|---|
| Red | ~700 |
| Orange | ~610 |
| Yellow | ~580 |
| Green | ~550 |
| Blue | ~470 |
| Indigo | ~445 |
| Violet | ~400 |
Light purple falls between violet and pink on the visible spectrum, corresponding to wavelengths of approximately 400-520 nm.
The Relationship Between Wavelength, Frequency, and Energy
Electromagnetic radiation behaves simultaneously as a wave and a particle. As a wave, it is characterized by wavelength (λ) and frequency (f). As a particle, it is characterized by discrete packets of energy called photons. The energy (E) of a photon is directly proportional to its frequency but inversely proportional to its wavelength:
E = hf
where h is Planck’s constant (6.626 x 10-34 Joule-seconds).
Shorter wavelengths correspond to higher frequencies and higher photon energies, while longer wavelengths correspond to lower frequencies and lower photon energies.
We can use these relationships to determine the energy associated with different colors of visible light. Violet light with a wavelength of 400 nm has a higher frequency and higher energy than red light at 700 nm. Light purple wavelengths around 500 nm will fall somewhere in the middle in terms of energy.
Calculating the Energy of Light Purple Light
We stated earlier that light purple corresponds to visible wavelengths of approximately 400-520 nm. Let’s calculate the energy of light at the maximum wavelength of 520 nm:
λ = 520 nm = 520 x 10-9 m
f = c / λ
= (3 x 108 m/s) / (520 x 10-9 m)
= 5.77 x 1014 Hz
E = hf
= (6.626 x 10-34 J-s) x (5.77 x 1014 Hz)
= 3.82 x 10-19 J
So a 520 nm light purple photon carries approximately 3.82 x 10-19 Joules of energy.
We can repeat these calculations for other wavelengths within the light purple range. For example:
400 nm photon:
E = 6.63 x 10-34 J-s x (3 x 108 m/s) / (400 x 10-9 m) = 5.53 x 10-19 J
450 nm photon:
E = 4.98 x 10-19 J
500 nm photon:
E = 3.97 x 10-19 J
This demonstrates how the energy decreases as the wavelength increases across the visible light purple spectrum. Photons at the violet boundary carry over 5 x 10-19 J, while photons at the pink boundary carry under 4 x 10-19 J.
Comparing Light Purple to Other Visible Wavelengths
To put light purple’s energy into context, we can compare it to photons at other visible wavelengths:
| Color | Wavelength (nm) | Photon Energy (J) |
|---|---|---|
| Violet | 400 | 5.53 x 10-19 |
| Light Purple | 500 | 3.97 x 10-19 |
| Green | 550 | 3.49 x 10-19 |
| Yellow | 580 | 3.30 x 10-19 |
| Orange | 610 | 3.06 x 10-19 |
| Red | 700 | 2.75 x 10-19 |
This shows that light purple photons carry more energy than yellow, orange, and red photons, but less energy than violet and green photons. The energy differences correspond to the varying frequencies associated with each color’s wavelength.
Real-World Context
In the real world, what do these tiny photon energy quantities mean for light purple light? Some examples:
– Vision – When light purple photons enter our eyes, their energy triggers neural signals to our brain, allowing us to see that color. Different photon energies stimulate our color receptors differently, creating all the hues we perceive.
– Photosynthesis – Plants absorb light energy to fuel photosynthesis. Light purple photons provide some energy for this, but less than higher energy blue and violet photons.
– Solar cells – Photovoltaic solar panels convert absorbed photon energy into electrical energy. Light purple photons contribute modestly to solar cell currents. Higher energy photons are more efficiently converted.
– Lasers – Purple laser light consists of a tight beam of identical purple photons at a specific wavelength. Within the visible spectrum, violet lasers can impart more energy than light purple lasers.
– LEDs & displays – LEDs and screens produce colored light by emitting specific visible wavelength photons. Mixing red, blue, and green ratios allows different shades like light purple to be produced.
So while the energy of an individual light purple photon is miniscule, light at this wavelength has many practical applications because of its specific energy content. Our eyes perceive this energy as a distinctive color.
Conclusion
In summary, light purple corresponds to visible light wavelengths of approximately 400-520 nanometers. Due to the relationship between wavelength, frequency, and energy, light purple photons carry amounts of energy ranging from about 5.53 x 10-19 to 3.82 x 10-19 Joules. This places light purple in the middle portion of the visible spectrum, with more energy than longer wavelengths like red and orange, but less energy than shorter wavelengths like violet and blue. While tiny on the individual photon scale, this quantity of energy enables many useful applications of light purple and allows our eyes to distinguish its unique color. Understanding the energies associated with visible wavelengths helps illuminate how we experience color through the phenomenon of light.
