White Light- Spectrum, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 05:04 PM IST

In this article we are going to learn about what is white light, what is spectrum of white light, wavelength of white light, white light effect and white light colours.

What is light?

Light is a form of energy .Light reflects on an object which helps to view the object .

What is white light?

White light is the combination of all the colours of visible spectrum with equal intensity. All the colours of spectrums are equally distributed.

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White Light- Spectrum, FAQs

What is white light spectrum?

White light is the combination of seven visible spectrum colours. Visible light is alsodefi white light. The components of white light/light white are violet, blue, green, yellow, cyan, orange, and red .

white light image can be represented as follows:

white light image

A colourless daylight is nothing but white light. Light is an electromagnetic wave. All the frequencies of the visible range spectrum show electromagnetic radiation. Sunlight is an example of white light. This visible light appears as white light in the human eye .

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Newton’s wheel or disc:

According to Newton’s wheel in physics , different colours in a rotating disc appears as white as the wheel rotates . According to Newton the white light colors will be primary colours like, Violet , indigo ,blue ,green , orange ,red.

Newton’s wheel

By newton’s wheel experiment we can practically prove that white colour have primary constituent colours.

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Prism:

Prism also breaks the white light in its constituent colour lights. Though the different colour light have different frequencies and wavelengths, when white light goes through a prism it breaks the white light in the constituent colours .

Prism

Wavelength of red light is the largest and violet light wavelength is the shortest.

The visible light wavelength range for a human eye is 380 nm – 760 nm. The lights having higher or lower value are not visible to the human eye.

All these are mentioned in the white light spectrum worksheet answers/white light test.

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NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. Mention the frequency of white light.

White light consists of seven lights of distinct colours. They all have different frequencies.

2. Which are the colours present in the white light?

The white light is composed of/white light is made up of seven basic colours such as, violet , blue , green, yellow, cyan, orange, and red.

3. What type of energy is white light?

White light energy is a form of light energy.

4. Can white light be polarized?

Yes, white light can be polarized. Polarization refers to the orientation of light waves' oscillations. While individual wavelengths in white light can be polarized, the overall appearance remains white because polarization doesn't affect the mixture of wavelengths present in white light.

5. How does white light interact with transparent, translucent, and opaque materials?

Transparent materials allow white light to pass through with little scattering or absorption, maintaining its composition. Translucent materials scatter white light as it passes through, diffusing it but generally maintaining its white appearance. Opaque materials block or absorb white light, either reflecting it (appearing white) or absorbing certain wavelengths (appearing colored).

6. How does the atmosphere's composition affect the spectrum of sunlight reaching Earth's surface?

The atmosphere's composition significantly affects the spectrum of sunlight reaching Earth's surface. Gases like oxygen, nitrogen, and water vapor absorb specific wavelengths of light. For instance, ozone in the upper atmosphere absorbs much of the sun's ultraviolet radiation. This selective absorption modifies the spectrum of white light from the sun, impacting not only the light we see but also Earth's climate and ecosystems.

7. How does the inverse square law apply to white light sources?

The inverse square law states that the intensity of light decreases proportionally to the square of the distance from the source. For a point source of white light, this means that if you double the distance from the source, the intensity of light at that point will be one-fourth of what it was originally. This law is crucial in understanding lighting design, photography, and many other applications involving light propagation.

8. How does the phenomenon of Rayleigh scattering affect our perception of white light from the sun?

Rayleigh scattering is the scattering of light by particles much smaller than the light's wavelength. In Earth's atmosphere, this phenomenon affects shorter wavelengths (blue light) more than longer wavelengths. As a result, when white sunlight enters the atmosphere, blue light is scattered more, making the sky appear blue. This scattering also explains why the sun appears yellower or redder at sunrise and sunset when light must travel through more atmosphere to reach our eyes, with more blue light scattered away.

9. What is white light?

White light is a combination of all visible colors in the electromagnetic spectrum. It appears white to our eyes because it contains a balanced mixture of all wavelengths of visible light, typically ranging from about 380 to 700 nanometers.

10. Can white light be created by mixing colored lights?

Yes, white light can be created by mixing colored lights. This is called additive color mixing. Specifically, combining red, green, and blue light in equal intensities produces white light. This principle is used in many electronic displays and lighting systems.

11. What is the difference between white light and monochromatic light?

White light contains a mixture of all visible wavelengths, while monochromatic light consists of a single wavelength or a very narrow band of wavelengths. For example, laser light is typically monochromatic, while sunlight is a form of white light.

12. How does the human eye perceive white light?

The human eye perceives white light when all three types of cone cells (responsible for color vision) are stimulated roughly equally. These cones are sensitive to red, green, and blue light. When white light enters the eye, it activates all these cones in a balanced way, leading to the perception of white.

13. What is the relationship between white light and the visible spectrum?

White light encompasses the entire visible spectrum. When white light is dispersed, it reveals the continuous spectrum of visible colors, from red (longest wavelength) through orange, yellow, green, blue, indigo, to violet (shortest wavelength). This visible spectrum represents only a small portion of the entire electromagnetic spectrum.

14. How does a prism separate white light into different colors?

A prism separates white light into different colors through a process called dispersion. As light enters the prism, it bends (refracts) at different angles depending on its wavelength. Shorter wavelengths (like blue) bend more than longer wavelengths (like red), causing the light to spread out into a spectrum of colors.

15. Why does a rainbow form after rain?

Rainbows form when sunlight interacts with water droplets in the air. Each droplet acts like a tiny prism, refracting and reflecting sunlight. Different wavelengths of light exit the droplet at slightly different angles, separating the white light into its component colors. The arc shape occurs because of the specific angle at which this separated light reaches our eyes.

16. How does the atmosphere affect white light from the sun?

The Earth's atmosphere affects sunlight through scattering and absorption. Shorter wavelengths (blue) are scattered more than longer wavelengths (red), which is why the sky appears blue during the day. During sunrise and sunset, sunlight travels through more atmosphere, scattering more blue light and allowing more red and orange light to reach our eyes.

17. What is metamerism in the context of white light and color perception?

Metamerism is the phenomenon where two color samples appear identical under one light source but different under another. This occurs because different combinations of wavelengths can produce the same color perception in our eyes. It's particularly relevant when dealing with white light sources of different spectral compositions.

18. How does the concept of "white balance" in photography relate to white light?

White balance in photography refers to adjusting the color temperature of an image to make white objects appear truly white. Different light sources (sunlight, fluorescent, incandescent) have different color temperatures, affecting how colors appear. Proper white balance ensures that white light in the scene is accurately represented, maintaining natural color appearance in the photograph.

19. How does the concept of metameric pairs relate to white light?

Metameric pairs are two color samples that appear identical under one light source but different under another. This phenomenon occurs because different combinations of wavelengths can stimulate our eye's color receptors in the same way. Understanding metameric pairs is crucial in industries like textiles and paints, where colors must match under various white light sources.

20. What is the difference between luminous efficacy and luminous efficiency in the context of white light sources?

Luminous efficacy refers to the ratio of luminous flux (perceived brightness) to power input, measured in lumens per watt. It's a measure of how efficiently a light source converts electrical power into visible light. Luminous efficiency, on the other hand, relates to how effectively a light source produces visible light that matches the sensitivity of the human eye. A high luminous efficiency means the light source produces more light in wavelengths that the human eye is most sensitive to.

21. What is the role of white light in circadian rhythms?

White light, particularly its blue component, plays a crucial role in regulating circadian rhythms – our internal biological clocks. Exposure to blue-rich white light during the day helps maintain alertness and regulates the production of melatonin, a hormone that induces sleep. This is why excessive exposure to blue light from screens at night can disrupt sleep patterns. Understanding this has led to the development of "warm" white light sources for evening use and blue light filters for electronic devices.

22. What is the significance of Fraunhofer lines in the solar spectrum?

Fraunhofer lines are dark lines that appear in the solar spectrum when it is viewed at high resolution. These lines represent specific wavelengths of light that are absorbed by elements in the sun's outer layers and Earth's atmosphere. Studying these lines allows scientists to determine the composition of the sun and other stars. They demonstrate that while sunlight appears as continuous white light, its spectrum actually has gaps at specific wavelengths.

23. How does the concept of color constancy relate to our perception of white light?

Color constancy is the ability of the human visual system to perceive the color of objects as relatively constant under varying illumination conditions. This is particularly relevant to white light because our brains adjust our perception based on the ambient light. For example, a white paper will still appear white under both warm incandescent light and cool fluorescent light, even though the actual wavelengths reflecting off the paper are different. This adaptation helps us navigate and recognize objects in different lighting environments.

24. What is the relationship between white light and black body radiation?

Black body radiation refers to the electromagnetic radiation emitted by an idealized physical body that absorbs all incident electromagnetic radiation. The spectrum of this radiation depends on the temperature of the body. As the temperature increases, the peak of the emission spectrum shifts towards shorter wavelengths. At around 6500K, the spectrum closely resembles that of daylight. This concept is fundamental to understanding the nature of white light from thermal sources like the sun and incandescent bulbs, and it forms the basis for defining color temperature in lighting.

25. How does the phenomenon of dispersion relate to the speed of light in different media?

Dispersion occurs because the speed of light in a medium depends on its wavelength. In most transparent materials, shorter wavelengths (like blue light) travel slower than longer wavelengths (like red light). This variation in speed causes different colors to refract at slightly different angles when entering or leaving a medium, leading to the separation of white light into its component colors. This principle explains not only how prisms work but also phenomena like chromatic aberration in lenses.

26. What is the significance of the D65 standard illuminant in colorimetry?

The D65 standard illuminant is a theoretical source of white light that approximates average daylight. It has a correlated color temperature of approximately 6500K and is widely used as a standard reference in colorimetry, the science of color measurement. This standard is crucial for ensuring consistency in color reproduction across different industries, from printing and textiles to display technologies. Understanding D65 helps in calibrating devices and ensuring accurate color representation under standardized "white light" conditions.

27. What role does white light play in the phenomenon of fluorescence?

White light plays a crucial role in fluorescence by providing the excitation energy needed for the process. When certain materials absorb white light, they re-emit light at a longer wavelength. For example, a fluorescent material might absorb ultraviolet light (part of the broader white light spectrum) and emit visible light. This principle is used in fluorescent lighting, where UV light from excited mercury vapor causes a phosphor coating to fluoresce, producing visible white light.

28. How does the concept of color temperature relate to the blackbody radiation curve?

Color temperature is directly related to the blackbody radiation curve. It refers to the temperature (in Kelvin) at which a theoretical black body would need to be heated to produce light of a particular color. Lower color temperatures (2700-3000K) correspond to warmer, more reddish light, while higher temperatures (5000K+) correspond to cooler, more bluish light. This concept allows us to describe the quality of white light sources in terms of their apparent warmth or coolness, based on their similarity to black body radiators at different temperatures.

29. How does the absorption of certain wavelengths affect the perception of white light?

When white light interacts with an object, certain wavelengths may be absorbed while others are reflected. The reflected wavelengths determine the color we perceive. If an object absorbs all wavelengths equally and reflects them all, it appears white. If it absorbs all wavelengths and reflects none, it appears black.

30. What is color temperature in relation to white light?

Color temperature refers to the apparent color of a white light source, measured in Kelvin (K). Lower color temperatures (2700-3000K) produce a warm, yellowish-white light, while higher color temperatures (5000K and above) produce a cooler, bluish-white light. This concept is based on the color a black body radiator would emit at different temperatures.

31. How do fluorescent lights produce white light?

Fluorescent lights produce white light through a two-step process. First, electricity excites mercury vapor to emit ultraviolet (UV) light. Then, this UV light strikes a phosphor coating inside the tube, causing it to fluoresce and emit visible light. The combination of different phosphors is designed to produce light that appears white to our eyes.

32. What is the role of white light in photosynthesis?

White light plays a crucial role in photosynthesis as it provides the full spectrum of visible light. Plants primarily use red and blue wavelengths for photosynthesis, but the other wavelengths in white light contribute to various plant processes. The ability to use a broad spectrum allows plants to adapt to different light conditions.

33. What is the difference between incandescent and LED white light?

Incandescent bulbs produce white light by heating a tungsten filament until it glows, emitting a continuous spectrum similar to blackbody radiation. LED (Light Emitting Diode) white light is typically produced by combining a blue LED with a yellow phosphor coating, or by mixing red, green, and blue LEDs. LED light often has a different spectral composition compared to incandescent light, which can affect color rendering.

34. Can white light be created without using the visible spectrum?

While white light is typically associated with the visible spectrum, the perception of white can be created without using the full visible spectrum. For example, combining specific wavelengths of red, green, and blue light can trick our eyes into perceiving white. This principle is used in displays and LED lighting, where "white" is created using a limited number of specific wavelengths.

35. How does white light relate to the concept of color rendering index (CRI)?

The Color Rendering Index (CRI) measures how accurately a light source reveals the colors of objects compared to a reference light source (usually natural daylight). A high CRI (closer to 100) indicates that the white light source renders colors more naturally and accurately. This is important in applications where color accuracy is crucial, such as in art galleries or retail lighting.

36. What is the significance of Planck's radiation law in understanding white light?

Planck's radiation law describes the electromagnetic radiation emitted by a black body at a given temperature. This law is fundamental to understanding the spectrum of white light emitted by thermal sources like the sun or incandescent bulbs. It explains why these sources produce a continuous spectrum and how the peak wavelength and overall spectral distribution change with temperature.

37. What is the relationship between white light and complementary colors?

Complementary colors are pairs of colors that, when combined in the right proportions, produce white light in additive color mixing. For example, blue and yellow are complementary colors. This concept is based on how our eyes perceive color and is fundamental to color theory in art and design. Understanding complementary colors helps explain why certain color combinations appear vibrant or balanced.

38. How does coherence (or lack thereof) characterize white light?

White light from most natural and artificial sources is incoherent, meaning the light waves are not in phase with each other. This is in contrast to laser light, which is coherent. The incoherence of white light results from it being a mixture of many wavelengths and from the random emission of photons by countless atoms in the light source. This property of white light affects how it interacts with matter and is crucial in understanding phenomena like interference and diffraction.

39. How does the concept of metamerism challenge our understanding of "true" white light?

Metamerism challenges our understanding of "true" white light by demonstrating that our perception of white can be created by different combinations of wavelengths. Two light sources may appear identical to the human eye, yet have different spectral power distributions. This means that what we perceive as white light can vary significantly in its actual composition. This concept is crucial in lighting design, color matching, and understanding the limitations of human color perception.

40. What is the importance of the CIE 1931 color space in defining white light?

The CIE 1931 color space is a standardized system for quantifying and representing all colors visible to the human eye. It's particularly important for defining white light because it provides a mathematical model for describing the chromaticity (color quality) of light sources. The color space includes a "white point," which serves as a reference for what is considered perfectly white light. This standardization is crucial for ensuring consistency in lighting applications, display technologies, and color reproduction across various industries.

41. What is the relationship between white light and the phenomenon of interference?

Interference is a phenomenon where light waves superpose to form a resultant wave of greater or lower amplitude. With white light, interference can lead to interesting effects because it contains multiple wavelengths. When white light undergoes interference, different wavelengths interfere constructively or destructively at different points, often resulting in colorful patterns. This is seen in soap bubbles or oil slicks, where thin films create interference patterns that separate white light into its component colors.

42. How does the concept of spectral power distribution (SPD) help in characterizing white light sources?

Spectral Power Distribution (SPD) is a graph showing the radiant power emitted by a light source at each wavelength across the visible spectrum. For white light sources, SPD is crucial as it reveals the exact composition of wavelengths that create the perceived white light. Different white light sources can have very different SPDs while still appearing white to the human eye. Understanding SPD is essential for assessing color rendering properties, energy efficiency, and the potential effects of light on human health and circadian rhythms.