Green is one of the colors visible to the human eye. It occupies a portion of the visible spectrum between blue and yellow. When white light, which contains all the colors of the spectrum, shines on an object that appears green, it means that object is absorbing all wavelengths except for those corresponding to green. This means that green objects absorb every color except green.
To understand which wavelengths green absorbs, we first need to understand a bit about light and color. Visible light consists of electromagnetic radiation with wavelengths between approximately 400-700 nanometers. The visible spectrum can be divided into different color regions, with violet and blue at the short wavelength end, and red at the long wavelength end. Green falls somewhere in the middle, around 500-565 nm.
When an object appears green, it means the object is reflecting light mostly in the green wavelength region back to our eyes. At the same time, it is absorbing all the other wavelengths. So a green leaf, for example, absorbs wavelengths corresponding to violet, blue, yellow, orange and red light. It reflects mostly green.
The Visible Spectrum
The visible light spectrum can be represented as a continuous band of colors from violet to red:
| Color | Wavelength range (nm) |
|---|---|
| Violet | 380-450 |
| Blue | 450-495 |
| Green | 495-570 |
| Yellow | 570-590 |
| Orange | 590-620 |
| Red | 620-750 |
As the table shows, green light occupies a wavelength range of approximately 495-570 nanometers. This range corresponds to the green portion of the spectrum.
When green is perceived, it means only the green wavelengths are being reflected or transmitted while other colors are being absorbed. So the key wavelengths that green absorbs are:
- Violet: 380-450 nm
- Blue: 450-495 nm
- Yellow/orange: 570-620 nm
- Red: 620-750 nm
The absorption of these other colors, while reflecting green wavelengths, is what gives rise to the perception of green.
Absorption and Reflection
The selective absorption and reflection of different wavelengths is what gives objects their color. When light strikes an object, several things can happen:
- Some wavelengths are absorbed
- Some wavelengths are reflected
- Some wavelengths are transmitted through
The wavelengths that are reflected determine what color our eyes see. For a leaf to appear green, it absorbs violet, blue, yellow, orange and red light. The green wavelengths get reflected back to our eyes.
The absorption and reflection of light depends on the atomic and molecular structure of the material. In plants, green color arises from chlorophyll pigments which have a special molecular structure that absorbs red and blue light very efficiently.
The transmitted light is the light that passes through the object. Transparent materials like glass transmit most visible wavelengths. Opaque objects like leaves transmit very little light.
So in summary, the key wavelengths absorbed by green objects are:
| Absorbed Wavelength Range |
|---|
| Violet: 380-450 nm |
| Blue: 450-495 nm |
| Yellow/Orange: 570-620 nm |
| Red: 620-750 nm |
While the green wavelengths from approximately 495-570 nm are reflected back to the eyes.
Why Do Objects Absorb Certain Wavelengths?
As mentioned earlier, the absorption of light depends on the atomic and molecular composition of a material. In colored pigments like chlorophyll, there are special chemical structures that can preferentially absorb certain wavelengths.
For example, the conjugated double bonds between carbon atoms in chlorophyll molecules can absorb visible light. The specific pattern of bonds absorbs red and blue light very efficiently, while reflecting green.
In metals and semiconductors, light absorption is dependent on the electron energy levels. When the energy of a photon corresponds to the gap between two electron energy levels, the photon can be absorbed to excite an electron. This selective absorption of light leads to metallic colors.
The structural composition and energy levels vary for different materials, leading to selective absorption and reflection properties. Even small changes can shift the wavelengths that get absorbed versus reflected. This is why we see such a diverse palette of colors among objects around us.
Applications of Light Absorption
The phenomenon of selective light absorption has many useful applications:
- Photosynthesis – Plants absorb blue and red light through chlorophyll to power photosynthesis. The green wavelengths get reflected, making plants appear green.
- Vision – Our eyes contain photoreceptor cells that absorb specific wavelengths to detect color. Color blindness occurs when certain photoreceptors are missing or defective.
- Photodetectors – Photodetectors like camera sensors work by absorbing photons to generate electric signals. Their sensitivity depends on the wavelengths they are designed to absorb.
- Solar cells – Solar panels contain materials like silicon that can absorb photons and convert them into electricity through the photovoltaic effect.
- UV protection – Sunglasses and filters contain compounds designed to absorb harmful ultraviolet light while transmitting visible wavelengths.
So in summary, the selective absorption of light is a fundamental optical process with a wide array of uses across biology, technology and consumer applications.
Conclusion
When an object appears green, it means it is absorbing all visible wavelengths except green light. Specifically, green objects absorb light in the violet (380-450 nm), blue (450-495 nm), yellow/orange (570-620 nm) and red (620-750 nm) ranges. The selective absorption of color is what gives rise to the diverse palette of natural colors we see in objects around us. It depends on the unique atomic and molecular composition of materials, along with their electronic properties. Harnessing the wavelength dependence of light absorption has enabled many useful technologies and applications. Overall, absorption and reflection of specific bands of color are the underlying reasons we are able to perceive the vivid green hues found everywhere in the natural world.