White surfaces are composed of molecules or atoms that don't absorb any of the visible colors of light;
Colors of objects
We usually view objects when they are illuminated by white light, usually sunlight or ordinary room light. White light is a mixture of all colors, in roughly equal proportions. White objects look white because they reflect all the visible wavelengths of light that shine on them - so the light still looks white to us. Colored objects, on the other hand, reflect some of the wavelengths; the rest they absorb. For example, if white light shines on a red ball, the ball reflects mostly red light, and so we see red. Most of the greens and blues that are part of white light are absorbed by the ball, so we cannot see them. Likewise, a blue book is reflecting the blue part of the white light spectrum. The red and green parts are absorbed by the book.
What happens when a red light shines on a red ball?
It continues to reflect the red light, and so it is still red -- but a white ball would also look red in red light, because it reflects all colors. If instead we shine blue light on a red ball, it will look dark, because it does not reflect blue light. It cannot look red unless there is red light coming to it from the light source. And it cannot look blue because the red ball absorbs blue light. So when we ask what color an object is, the answer is not simple - it depends on what color light we are using to see the object.
One consequence of the fact that different colored objects absorb different wavelengths of light is that darker objects heat up faster in the sun than white ones do - because they absorb many of the different wavelengths of light energy, while white objects reflect most of the wavelengths.
Which Colors Reflect More Light?
When light strikes a surface, some of its energy is reflected and some is absorbed. The color a person perceives indicates the wavelength of light being reflected. White light contains all the wavelengths of the visible spectrum, so when the color white is being reflected, that means all wavelengths are being reflected and none of them absorbed, making white the most reflective color.
From Total to Zero Reflectivity
If the color of a surface is anything other than white, it means that it absorbs light of some wavelengths. For example, a surface that appears red absorbs yellow, green, blue and violet light, while reflecting red light. A surface that appears green absorbs all colors except green. White light is a combination of all colors -- as is apparent when you shine a white light through a prism -- so anything that appears white reflects all wavelengths of light. Black is the least reflective color, it's the color of a surface that absorbs all light.
Tints and Shades
If a surface isn't white, then the closer its color is to white, the more light it reflects. Pastel and off-white colors reflect more light than deep tones. Adding white to a color is called tinting the color, and it increases the color's reflectivity. The contrasting procedure is to add black to decrease the reflectivity. This is called shading.
Different Colors in Different Lights
An object that is white, would look red in a red-colored light because white contains all colors. But if a blue light were shined on a red ball, the color on the ball would be very dark, because the red color only contains red, not blue, so it absorbs the blue light instead of reflecting it. The color of an object depends on the light cast upon it. The only way to know the color of an object is to put it into sunlight or white light.
Heat Absorption
Darker colored objects heat up faster in the sun than light colored ones, which is why running across asphalt in bare feet can feel much hotter than walking across light-colored concrete. The reason is that darker colors absorb more of the different wavelengths of light energy, while white or light-colored objects reflect the light of most wavelengths.
What Colors Absorb More Heat?
Heat energy obeys the same laws of conservation as light energy. If a certain substance reflects most light wavelengths, most heat energy will be reflected as well. Therefore, due to the nature of visual light, colors that reflect most wavelengths of light tend to be cooler than those that only reflect a few. Understanding how this principle applies to different colors can allow a person to stay warmer or cooler simply by wearing different colored clothes.
Dark Colors
Dark colors absorb a lot more heat than lighter ones because they absorb more light energy. In fact, the closer to black a color is, the more heat it absorbs from light sources. The key is that colors do not absorb different amounts of heat, only heat from light. Dark and light colored clothes coming out of a dryer will be the same temperature. However, because light clothes reflect more light when a person is outside, the accompanying heat from the sun is reflected as well. Since dark clothes reflect little solar light, they reflect little solar heat and are hotter as a result.
Bright Colors
Colors like pink or yellow are often called "bright" because of the high degree of light they reflect back. Visual light is composed of numerous different colored wavelengths, which make a white light when combined. Therefore, light colors such as pastel yellows or pinks are perceived that way because most light wavelengths are reflected back to our eyes. Since most light is reflected, little light (or heat) is absorbed.
Shiny Colors
While color is the primary factor, other variables can affect how colors absorb heat. Shiny colors are able to reflect significant amounts of light and heat compared to flat colors. Even darker colors can reflect most heat they are exposed to if they have a reflective sheen. Regardless, the heat absorption hierarchy of colors will always remain if all other factors are equal. A shiny deep blue will still absorb more heat than a shiny yellow.
Black and White
Black is the ultimate heat absorber. It absorbs all light on the visual spectrum, creating a void of light. As a result of absorbing all light wavelengths, black is the hottest possible color. White is the opposite. White light is the sum of all wavelengths, so when some people view a white object, they are really viewing all visible light hitting the object's surface and reflecting back. Some heat is still absorbed based on the nature of the object's material, but minimal additional heat is absorbed, making white the coolest possible color.
What Colors Attract Heat?
To keep cool on a sunny day, the color of your clothes may matter more than the length or material. Have you ever wondered why you feel cooler in a long-sleeved white shirt than you do in a black T-shirt? It all comes down to color. The color of an object is determined by the wavelengths of light that object absorbs, and because absorbed light transforms into thermal energy (heat), darker colors attract more heat.
Light and Color
Light is a type of electromagnetic radiation that moves outward from the source in waves. Though we see light as uniform, it consists of a broad range of wavelengths in a variety of colors depending on frequency – some visible and some invisible to the human eye. Color is a measure of which of these wavelengths is or is not absorbed by a given object. All other wavelengths reflect off the object.
Light and Heat:
Heat is a measure of the movement of molecules in an object. The more the molecules move, the warmer the object becomes. Wavelengths of electromagnetic radiation resonate with molecules when the radiation is absorbed, setting them into motion and increasing heat. The more wavelengths of radiation that are absorbed, the more heat is attracted. Even objects that reflect all colors still absorb some wavelengths of radiation. The longest of these wavelengths, known as infrared light, is invisible to the eye.
White and Black :
White and black, stand at opposite ends of the color spectrum. White objects reflect all visible wavelengths of light, while black objects absorb all visible wavelengths. As a result, these two colors attract the least and the most heat, respectively. However, even white objects attract heat by way of infrared light – no color attracts no heat.
Rainbows and Radiation
Falling between white and black, objects of a given color attract heat based on how many wavelengths, of visible light they reflect. Wavelengths, of higher frequency, result in darker colors, resulting in more absorbed heat. Red objects attract the least heat after white objects, followed by orange, yellow, green, blue, indigo and violet, which attracts the most heat of any visible color other than black.
Keeping Cool, Staying Warm
To stay cool during the summer and keep warm during the winter, keep this rule of thumb in mind. White, red and yellow are best for the warm months when you want to avoid attracting extra heat. In cool months, those same colors are best traded for blue, violet or black when you want to trap as much heat as possible. This is why you aren’t supposed to wear white after Labor Day.
How to Calculate Reflectance:
Reflectance is a measure of the incident electromagnetic radiation that is reflected by a given interface. It is closely related to reflectivity but reflectance is more applicable to thin reflecting objects. Reflectance can vary for thin objects due to variations in the surface thickness and approaches the reflectivity as the surface becomes thicker.The reflectance may be calculated by comparing the amount of reflected radiation to the amount of incident radiation.
The Steps
Calculate reflectivity. Reflectivity can be calculated as p(y) = Gr(y)/Gi(y) where p is the reflectivity, y is the wavelength of the light, Gr is the reflected radiation and Gi is the incident radiation.
Calculate reflectance from the reflectivity. Reflectance is the square of the reflectivity, so q(y) = (Gr(y)/Gi(y))^2. where q is the reflectance, y is the wavelength of the light, Gr is the reflected radiation and Gi is the incident radiation.
Determine the units of measure for reflectance. The incident and reflected radiation must be measured in the same units so their ratio has no units. Reflectance is therefore a dimensionless number without units.
Interpret the reflectance value. The reflected quantity of radiation must be non-negative, and the incident radiation will be positive. The reflected radiation can never be greater than the incident radiation, so reflectance ranges from 0 to 1 such that 0 indicates no radiation was reflected and 1 indicates that all the light was reflected.
Calculate the reflectance for specific conditions. For example, say that a polished gold surface subjected to direct radiation with a wavelength of 480 nanometers reflects about 60 percent of that radiation. In this case, the reflectance would be q(y) = (Gr(y)/Gi(y))^2 = .6^2 = .36, or about 36 percent.
What Color of Light Do Plants Absorb?
Plants survive by using photosynthesis, which is a fancy way of saying that they use light to make their own food. But light comes in all sorts of colors, meaning that plants have the entire rainbow at their disposal when they are in full sunlight. Which color of light do plants absorb? Hint: it’s not green.
Why Do Plants Appear Green?
You might be surprised to find out that plants don’t absorb green light. So why do plants look green? Think about it this way: When you look in a mirror, that mirror reflects light back at your eyes. That explains how you can see your reflection on its surface. You see green when you look at a leaf because it is reflecting that light while absorbing others. The color most associated with plants is the color they are turning away.
What Colors Do Plants Absorb?
Photosynthesis works by absorbing light and using the energy from that light to make sugars the plant can use. The light plants can use for photosynthesis is called photo synthetically active radiation, and it just happens to be the same spectrum of light that we can see. Plants absorb light by using pigments called chlorophyll, which are really good at harnessing the energy from light as they absorb it.
Of those chlorophyll pigments, the primary one is called chlorophyll a. It doesn’t absorb all wavelengths, equally. In fact, it’s a little picky about what it picks up. Think about the colors of the rainbow (red, orange, yellow, green, blue, indigo and violet, in that order).
Chlorophyll a picks up some red and orange light while it reflects yellow, green and blue. Its favorite colors, though, are indigo and violet, as it absorbs those colors at nearly double the rate it picks up red and blue. There are other pigments in leaves as well, like chlorophyll b, which absorbs some slightly different wavelengths, and beta-carotene, which reflects red through green while absorbing a bunch of blue.
What Color Is Best For Plants?
To perform photosynthesis, violet light is the most important color, and it's from these wavelengths, that plants get most of their energy. The reason for this is because out of the visible spectrum, red light is the longest wavelength light that the photosynthesis process can use, but it has the least energy. As we move through the spectrum from red, wavelengths, become shorter and shorter while energy increases. Violet light is the shortest wavelength, and it has the highest energy.
Why Aren’t Plants Black?
Plants are typically green because they reflect green and yellow light, but if they absorbed all colors equally, they would appear black. While some plants do, in fact, have black leaves, this is definitely not the norm. If photosynthesis is all about harvesting energy from light, then why not use all of it?
Plants likely don’t absorb all wavelengths, equally because it’s possible that would be harmful to them. Just like staying in the sun too long burns your skin, absorbing too much light could actually interfere with photosynthesis by heating up the leaf and damaging it. The solution? Absorb some and reflect the rest.
The reason why green light is reflected as opposed to red is largely unknown. Some scientists believe it evolved as a way to avoid over saturation, while others believe that chlorophyll photosynthesis evolved in the deeper layers of the ocean at a time when photosynthesizing bacteria called halo bacteria were dominant on the ocean’s surface.
Halo bacteria use pigments that absorb green light and reflect purple, meaning that the only available light beneath the surface would be purple, not green. As halo bacteria began to die off, chlorophyll photosynthesis took over.
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