Introduction of white light
The complete blend of all the wavelengths of the visible spectrum is known as white light. This indicates that if a person has a beam of light that includes all the colors of the rainbow, and focuses all of them onto a single spot, the combination of all colors will result in a beam of white light.White light or visible light comes above infrared rays. At its zenith power, the Sun emits visible light. However, the entire emission power spectrum passes all wavelengths which shows that the Sun emits slightly more infrared than visible light.
What is White Light?
A beam of white light is a mixture of all colors of light. When white light is used to illuminate a colour screen, the mix will have all colors of the visible spectrum. To enhance the quality of the image there is an effect called "contrast". White light (the mixture of all colors) will have a contrast value of 0. By adding blue light the contrast is increased to 1. With red, green and yellow, the white light has a contrast of 3. By adding cyan and infrared light, the contrast is increased to 4. Adding ultraviolet, gives the white light a contrast of 5.
The more lights used, the higher the contrast. Many factors influence the contrast in an image. The same screen can produce images with a higher contrast when the light source is blue, while another screen produces better contrast with white light. The brain perceives color and light sources. It's the light that is "seen" but not the actual stimuli in which it's presented. Adults have the complete spectrum of light available to them, so if they need to change something that they don't know if they would be able to do it. The simple fix is to introduce white light instead of blue light.
Neon lights are the only coloured lights that our eyes are not able to properly distinguish from white light. Neon lights are usually compact and can be of a small part of the tube. They are not used in normal neon lights but in signs as we will see later. Overhead fluorescent tubes can make everything as white as possible by twisting the bulb, and twisting it will give you a "rainbow". This is similar to "Neon lights".A twisted bulb can still be labeled as "Neon" not "Fluorescent". The purpose of this is to have a light that resembles natural sunlight more than any artificial light. People who have not visited "Neon Alley" would believe that neon lights are just as bright as fluorescent lights, but "Neon" light is brighter than any type of lighting.
Electromagnetic Spectrum
Electromagnetic spectrum comprises different types of electromagnetic waves, each with different wavelengths or frequencies. For example, gamma rays, infrared radiation, x-rays, and ultraviolet radiations are examples of electromagnetic waves. The human eye can only see a small portion of the spectrum of wavelengths. The visible spectrum is also known as the visible portion of the electromagnetic spectrum. This shows the full spectrum of electromagnetic radiation and highlights the small part of the spectrum that is the visible spectrum.
Light Spectrum Definition
The variety of wavelengths of energy produced by a light source is known as the light spectrum. The unit of measurement of light is nanometers (nm). Each wavelength of the light or band of light energy is represented by a nanometer and has a spectrum of visible light within the range of 380 mm to 780 mm.Here the light spectrum can mean the visible spectrum. Visible spectrum implies the light spectrum, the range of wavelengths of electromagnetic radiation that our eyes are sensitive to, or the mean plot (or chart or graph) of the intensity of light against its wavelength (sometimes, its frequency).
Light refers to what we see or to a piece of the electromagnetic spectrum that operates on the optical telescope (especially on the ground) and sometimes, irregularly, which means the entire electromagnetic spectrum or any electromagnetic radiation.Therefore, we can say that spectrum is the splitting of white light into its constituent colors when passed via a prism. However, it can also be done on the light having more than one constituent color where the frequency need not be just white light.
How is White Light Produced?
White light can be generated by a variety of white light sources, both in space and artificial sources on earth. For example the stars and the Sun are the sources of white light. The obvious source of white light in the solar system is the Sun. The white LED's and fluorescent light bulb producing white light is an artificial source of light. However, unlike the incandescent lamp, other light bulbs do not produce white light. It produces light of a much longer wavelength within the red to yellow range.
The Wavelength of White Light
Depending on the wavelength, one can see the visible light color. Above 700 mm and below 400 mm, light is not visible. White light is made up of seven colors viz: violet, green, indigo, orange, blue, yellow, and red. Here, the wavelength of red is 400 mm, and that of violet is 700 mm. Hence, white cannot be assigned to a single wavelength as it is composed of wavelengths of different colors.The white light has a wavelength between the ranges of 400 – 700 mm.
Characteristics of White Light
The so-called white light is all around us. Most of the light coming from the sky or our home and office light allows us to see things. It can also be said that life on the planet provides both heat and energy.
When white light is transmitted from the prism or diffraction grating, the colors of the visible spectrum appear.
Colors vary according to their wavelengths
Violet has the highest frequency and the shortest wavelengths, and red has the lowest frequency and the longest wavelengths.
Difference Between White Light and Sunlight
White Light
A blend or mixture of colors is known as white light, which gives the eye sensation of white. As we know, if the green, red, and blue light is mixed in the proper portion, we get the white light. Many combinations of light give white light.
Every white light does not have a continuous spectrum. When we energize the hydrogen gas, it emits white light while its spectrum is distinct.
Sunlight
Sunlight is the combination of all wavelengths of the visible region spectrum of the Sun. Simply put, it is the radiation of the Sun in the visible region. Also, sunlight gives our eyes the sensation of white; hence sunlight is known as the white light.
We also know that the sunlight spectrum is continuous. So sunlight is a subcategory of white light.
Applications of White Light
Many objects, including the Sun in space, are natural sources of white light. On earth, white LEDs and the white fluorescent bulbs are an artificial source of light. White light can be separated back to different colors with the help of a device like a prism.
Conclusion
White light or visible light is the part of the electromagnetic spectrum that can be identified by the human eye. White light or its near-infrared light is typically absorbed and emitted by the electrons in atoms and molecules that shift from one energy level to another. The chemical mechanism that triggers human vision and plant photosynthesis are based on this phenomenon.
FAQs on White Light
1. What is white light in physics?
In physics, white light is defined as polychromatic light, which means it is a combination of all the different colours or wavelengths of light visible to the human eye. This range of colours is known as the visible spectrum and is often remembered by the acronym VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red). Sunlight is the most common natural example of white light.
2. What colours combine to make white light?
White light is composed of the seven colours of the visible spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, and Red. Additionally, in the context of additive colour mixing, the three primary colours of light — Red, Green, and Blue (RGB) — can be combined in the right proportions to produce white light, a principle used in screens and displays.
3. What are the main properties of white light?
The key properties of white light, as studied in the CBSE syllabus, include:
- It is polychromatic, meaning it is composed of multiple colours and wavelengths.
- It travels in a straight line in a uniform medium.
- It undergoes dispersion, which is the splitting into its constituent colours when it passes through a medium like a glass prism.
- Its constituent colours can be recombined to form white light again.
4. How does a prism split white light into a spectrum of colours?
A prism splits white light through a phenomenon called dispersion. When white light enters the prism, it refracts or bends. However, the angle of bending depends on the wavelength of the light. Since each colour has a different wavelength, each one bends by a slightly different amount. Violet light (shortest wavelength) bends the most, while red light (longest wavelength) bends the least, causing the colours to separate into a visible spectrum.
5. If white light contains all colours, why do objects appear in different colours?
An object's colour is determined by the wavelengths of light it reflects when illuminated by white light. For instance, a leaf appears green because its surface absorbs most of the colours from the incoming white light but primarily reflects the green wavelengths back to our eyes. A white object reflects all colours, and a black object absorbs all colours.
6. How can the colours of the spectrum be recombined to form white light?
The colours of the spectrum can be recombined back into white light by reversing the process of dispersion. According to the NCERT curriculum, this can be demonstrated in two main ways:
- Placing a second, identical prism in an inverted position next to the first one. The second prism will merge the separated colours back into a single beam of white light.
- Using a Newton's disc, which is a circular disc painted with the seven colours of the spectrum. When the disc is spun at high speed, the colours blend together, and the disc appears whitish-grey due to the persistence of vision.
7. Is all white light the same? For example, how is sunlight different from the light from a white LED?
No, not all white light is the same in its composition. Sunlight produces a continuous spectrum, meaning it contains all the wavelengths of the visible spectrum without any gaps. In contrast, the light from a typical white LED produces a discontinuous or emission spectrum. It is often created by a blue LED coated with a yellow phosphor. The combination of blue and yellow light stimulates our eyes to perceive the light as white, but it may be missing some of the intermediate wavelengths found in sunlight.
8. Why does sunlight appear white, but the sky appears blue?
Sunlight appears white when we look towards the sun (not directly) because the composite mixture of all its colours reaches our eyes together. The sky, however, appears blue due to a phenomenon called Rayleigh scattering. As sunlight passes through the Earth's atmosphere, tiny air molecules scatter the shorter wavelengths (blue and violet) much more effectively than the longer wavelengths (red and orange). Since our eyes are more sensitive to blue than violet, we perceive the scattered light from all over the sky as blue.
