Incandescence vs Iridescence
What is Incandescence?
Incandescence is the process of producing light from a heated solid material. This light is in the visible electromagnetic radiation; therefore, we see it as a color. Other than that, from a hot object, other types of radiation can also be emitted (thermal radiation), but this is not considered as incandescence. The light is produced as a result of the increased temperature. Therefore, incandescence is a special type of thermal radiation. Basic principal of incandescence is giving energy to the atoms by heating. When a solid is heated, it turns to red first (at this point, the object emits enough radiation, so we can observe the color). Red is the lowest energy color in the visible range that we can observe. Then upon further heating it becomes white. We see it as white because we are giving enough energy to the material, so that the electrons in it are energized in so many different ways, and the collection of those can be observed as white light. For example, we see incandescence when an iron bar is heated to a high temperature. Then iron bar starts to glow in red and orange color, which we can see. Therefore, some of the supplied heat energy to the iron bar has turned into light energy. Incandescence is used in incandescent light bulbs to produce light. In these bulbs, a filament, which can withstand a very high temperature without melting, is used. The filament has a long lifetime too. When heating this filament, it emits radiation, which falls into the visible region, thus producing light. However, most of the radiation is emitted in the infrared part in the spectrum; therefore, we feel the heat. So the efficiency of the bulb is less in producing light. If there is an element, which can withstand a very high temperature, the efficiency could be high. Sunlight is also due to the incandescence of sun.
What is Iridescence?
Iridescence is an optical phenomenon where we see different colors as we change the angle of observing. Or the differences can be observed, if the angle of illumination changes. This is a property of certain surfaces. We can see surfaces like this in nature a lot. For example, butterfly wings, feathers of birds and shells of some animals, some parts of plants have this property. This is caused by changing the reflection of incidental radiation. During this process, some of the wavelengths in the incidental light can be amplified, and some can be attenuated. If the two light waves are in phase, they are amplified. If they are out of phase, destructive interference cancels them off. In multiple layers structures of animals, iridescence can be seen. This is due to thin film interference. For example, eyes of cats contain multilayer structures that improve night vision. Therefore, they produce iridescent metallic-like reflections.
What is the difference between Incandescence and Iridescence?
• Incandescence is the process of producing light from a heated solid material. Iridescence is an optical phenomenon where we see different colors as we change the angle of observing.
• For incandescence to take place, the object should be heated.