Electrical lighting was a phenomenal and outstanding invention in the late 19th century that has been a blessing to the world to date. There were various attempts of what could give the best light for a prolonged period by various scientists. Tungsten was the best settled for all the tested materials. The colour produced was orange-yellow which was close to morning sunlight. The desire of man was to produce light as natural as the sun that is white. However, the ideal is not practical, a statement that engineers are fond of saying repeatedly. At first, the man was satisfied with the light colour, in fact, he did not bother the colour, if only it could help him see his surrounding that was okay.
Visible Light and Colors
As diversification and complexity of lighting need grew, so was design and inventions. To get light of a given colour filters were applied. To date, colour filters are used when a certain colour is required and the input is white light. The principle of colour filters is such that a material absorbs all the other colours and allows only the selected colour to pass. Optics which is a branch of physics carried out extensive and intensive research on light and colours. The scientists established that light is both a wave and a particle. As a wave light travels at a given waveform, frequency, wavelength and amplitude. Different light colours have different wavelengths. White light is a combination of all colours while black is the absence of any light. Radiation which splits white sunlight into seven colours that form a rainbow explains the different wavelengths of light.
Tungsten filament as source of light
Light as a particle constitutes a discrete amount of energy. This means that light is a form of energy and this is key to note. The first law of thermodynamics states that energy cannot be created or destroyed. Light energy is produced when a conversion of another form of energy occurs. For tungsten filament, the electrical energy is converted into heat and light. The heat excites electrons which transition into higher energy levels. Since electrons are unstable in higher energy levels they free fall into lower and stable energy levels. Once the electron falls to a lower energy level it releases a discreet amount of energy called a photon. A photon produces light with a discreet wavelength. The light is a wave and it travels through space at a speed of 3x 10^8 m/s. since heating is continued the processing of excitation of electrons into higher energy levels and subsequent fall to lower energy levels produces continuous light. The wavelength of the photon determines its visibility nature, too higher and too low wavelength cannot be seen. The visible range is within 340nm-740nm of wavelength.
To realize different colors the material emitting light is heated at different temperatures and this excites electrons to different energy levels. The subsequent fall produces light with different wavelengths. The largest wavelength of visible light is 740nm giving red and the smallest is 340nm giving violet. When all full range of wavelengths is available white light results.
The invention of the light-emitting diode has caused a declining use of color filtered while at the same time enriched color diversity. When a semiconductor material is doped oppositely and made into a diode a junction is formed in between. When the diode is biased by applying an electric field in forwarding biased manner light is produced. Electric fields cause electrons to move across the junction and as they move, they collide with electrons in the junction. The collided electrons are energized into higher energy levels. Due to high instability, these electrons fall to a lower stable energy level emitting a photon of energy. The photon travels out like a light wave that is visible. Different semiconductors have the different formations of discrete energy levels and therefore produce different colors of light. There are 3 primary colors i.e., blue, green, and red. Once we produce a diode producing these three lights. Their switching can be modified so as to produce any other desired color (secondary colors).
- Today the entertainment industry has richly used Led lighting to add color and pomp to events, occasions, and fun facilities.
- Signage and advertising used Led to inform the intended audience of a given message. This is more pronouncement and eye-catching at night.
- Aviation industry- airfield visual guide employs visible light of different colors to communicate to the pilot. The extent of the runway, taxiway, and other facilities.
- Devices indicators- every gadget made today has a LED indicator to show when on, off among other functions.
- Power distribution- the industry has led indicator bulbs to show the presence of power, the occurrence of a fault, running of generators among other uses.
The invention of colored light was a big win in the engineering world. Whether it is filtered color or LEDs, the impact cannot be overestimated. The visible light is very important to man, apart from audio communication, all other forms require the presence of light. The research is ongoing and there is more to come to the betterment of life.