Understanding the Nature of Light

Nature of Light

• The nature of light is a long-standing scientific problem.
• Various theories have been developed over centuries to explain light's nature.
• Isaac Newton proposed the first scientific hypothesis in the late 17th century.
• Newton believed light comprised corpuscles emitted at high speed, traveling in straight lines.
• In 1704, Newton published "Optics," detailing the corpuscular theory and explaining phenomena like reflection, refraction, and diffraction.
• Christiaan Huygens developed the wave theory of light in 1678, arguing that light is a wave.
• Huygens explained phenomena like light ray interference, which the corpuscular model couldn't.
• Huygens' theory didn't gain traction initially due to Newton's prestige.
• Young and Fresnel's interference experiments and Foucault's work on light speed revived the wave theory in the mid-19th century.
• A problem with the wave theory was the need for a medium for wave propagation, making light's travel in a vacuum difficult to explain.
• James Clerk Maxwell resolved the problem by deducing that light is electromagnetic, based on Faraday's work on electric and magnetic fields, meaning it doesn't need a medium.
• This was called the electromagnetic theory of light.
• The theory couldn't explain the photoelectric effect or incandescent light emission.
• Albert Einstein developed a new theory based on Planck's quantum studies.
• Einstein proposed that light is formed by small energy packets called quanta, now known as photons.
• The problem with Einstein's theory is that it doesn't explain phenomena like interference.
• Currently, light is understood to have a dual nature, electromagnetic for propagation and corpuscular for matter interaction.

Electromagnetic Spectrum

• It is the set of all electromagnetic waves.
• Waves are classified by wavelength when propagating in a vacuum.
• Cosmic rays have very short wavelengths, while radio waves have the longest.
• The visible light range is of interest because its wavelengths can be detected by the human eye.
• Visible light is situated between ultraviolet and infrared radiations.
• It spans from approximately 380 nm (violet) to 780 nm (red).

Properties of Light

• Light behaves as an electromagnetic wave moving in a straight line in a vacuum.
• When light hits a separation surface between two mediums, part is reflected, part is refracted, and part is absorbed.
• Light reflection is when a light wave bounces off a separation surface between two mediums.
• Incident and reflected rays form the same angle with the surface normal.
• Refraction is the change in direction of a light wave due to a speed change when passing from one medium to another.
• Light maintains its frequency but changes propagation speed and wavelength during refraction.
• Mirages are examples of refraction when light bends upon entering a hot air layer above a surface.
• When light hits a surface, some of the wave is absorbed, creating a color sensation.
• For instance, if a surface absorbs all wavelengths except blue, the surface appears blue.

Color

• Color is a sensation produced by visible light perceived through the organs of vision.
• When an object is illuminated, it absorbs and refracts part of the electromagnetic waves and reflects the rest.
• The eye interprets the reflected wavelengths as colors.
• Black is the absence of visible light, while white can be decomposed into all colors.
• Newton discovered this when he passed white light through a prism and obtained the colors of the rainbow.
• A light ray with a different wavelength or color can be created from two luminous rays with different wavelengths.
• Illumination is when a set of three colors (red, yellow, and blue) creates the primary colors.
• The mixing of these colors leads to the other colors.
• Additive mixing is when colors are obtained by adding light rays, while subtractive mixing uses color filters on white light.
• Light waves perceived as color have properties affecting color perception, including hue, saturation, and brightness.
• Hue is the color itself, such as red, yellow, or violet.
• Saturation is the purity of a color, depending on the amount of white present in.
• The greater the saturation, the purer the color.
• Brightness is the amount of light emitted by a source, or reflected by a surface.
• High light quantity makes colors vibrant and intense, while low light quantity dulls colors.

Color Temperature

• A black body absorbs all incident energy.
• It emits radiation with a certain wavelength that varies with its temperature.
• It initially acquires a reddish tone, then progresses to orange, yellow, white, and finally blue as temperature increases.
• The color temperature of a light source is the temperature at which a black body emits the same color as the source.
• Color temperature is measured in Kelvin (K).
• For example, noon sunlight is similar to a black body heated to 5,500 K.
• Color temperature can only be defined for light sources with colors similar to a black body, like incandescent lamps.
• Light from lamps like low-pressure sodium vapor don't coincide with a black body so only approximate temperatures can be given.

Color Rendering Index

• Measures the ability of a light source to reproduce colors.
• The index defines the appearance of objects illuminated by a light source compared to their appearance under black body light.
• The maximum value, 100, refers to black body light.
• The chromatic reproduction measures the color of a light source is calculated by illuminating a certain sample.
• The smaller the difference between the color on the source and the sample, the better the chromatic reproduction.
• Lamps should have a chromatic reproduction index as close to 100 as possible to distinguish all colors.

Incandescent Lamps

• These lamps were the first electric artificial lighting devices.
• Carbon filament lamps were simultaneously developed by Thomas Alva Edison and Joseph Swan.
• Edison was granted the patent.
• The incandescent lamp has not changed much since its creation, but technology has produced improvements in light production, duration, and consumption.
• These lamps are simple to manufacture, use, and are cheap.
• An incandescent lamp usually consists of a threaded metal cap with a terminal at the end.
• The outside of the cap is the other terminal.
• The cap is attached to a glass bulb filled with a gas.
• Two copper wires connect to the terminals and attach to a tungsten filament in the center of the bulb.
• Inert gas fills the bulb to prevent oxygen from volatilizing the filament at high temperatures, increasing the life of the filament.

Incandescent Lamp Operation

• These lamps work by passing an electric current through a tungsten filament in the bulb.
• Electrically, the filament acts as a resistor.
• The current passing through the filament heats it via the Joule effect, causing it to emit visible radiation.
• This phenomenon is known as incandescence.
• Only a small fraction of electromagnetic radiation emitted by the filament is in the visible spectrum.
• Most of it is infrared radiation, resulting in a large quantity of heat.
• Light output of incandescent lamps ends up being very low.

Incandescent Lamp Characteristics

• Light color depends on the type of bulb, and produces yellowish light color.
• Transparent bulbs produce a yellowish light with color temperatures around 3,000 K and a high color rendering index.
• The stream of light is very limited and not constant throughout the lamp's life.
• Tungsten evaporation causes filament thinning and darkening of the bulb's inner wall, which leads to lighting depreciation.
• These lamps are very inefficient, producing 8 to 20 lm/W because much of the absorbed electrical power is lost as non-visible radiation.
• The lifespan depends on the filament's temperature.
• Higher temperature will increase the speed of filament evaporation and shorten the lamp's lifespan.
• Normal incandescent lamps last around 1,000 hours.

The Importance of Filament Temperature in Incandescent Lamps

• Not only does duration, but also the performance of incandescent lamps depends on filament temperature.
• Higher temperature leads to better performance, but decreases lifespan.
• The main factor that controls a lamp's influence is the power supply.
• Applying a voltage higher than the lamp's rating increases both power consumption and light output.
• Lamp life also decreases.
• If the lamp is powered with lower than the nominal voltage, the opposite happens.
• Light output decreases and its lifespan is increased.
• Incandescent lamps are generally classified as standard or halogen.

Halogen Lamps

• Standard incandescent lamps correspond with most incandescent lamps.
• Halogen lamps are a considerable improvement.
• Halogen, usually iodine, is added inside the bulb.
• The iodine reacts with evaporated tungsten, forming a compound that only decomposes in the hottest part of the filament.
• This process regenerates the tungsten, reducing net evaporation and allowing higher temperatures.
• Halogen lamps typically last twice as long as incandescent lamps (2,000 hours).
• Halogen lamps have a luminous efficacy up to around 22 lm/W.
• Dimensions of the the lamps are smaller.
• Standard incandescent lamps are used for general and localized indoor lighting in homes, businesses, and offices.
• Halogen lamps use high pressure and are commonly used for flood lighting in buildings, monuments, sports, etc.

Fluorescent Lamps

• These lamps are light sources with greater power efficiency compared to incandescent lamps.
• They are commonly used now.
• Incandescent lamps rely on incandescence.
• Light is emitted by a body subjected to very high temperatures.
• Fluorescent lamps use luminiscence, which happens in low or normal temperatures.
• Some electrons can reach a greater energy level when a certain form of energy strikes an atom, jumping to an upper orbit.
• When these electrons return to their basic state, they emit extra energy as a visible wavelength photon.
• This phenomenon is known as luminescence.
• Luminescence can be broken down into different types depending on which energy excites the atom.
• Electroluminescence is produced when an electric current passes a luminescent gas.
• Mercury vapor lamps at high pressure and sodium vapor lamps at high and low pressure utilize electroluminescence.
• Photoluminescence requires radiation by a light source within the UV or visible spectrum.
• Fluorescence is the class of photoluminescence.
• Fluorescent lamps use fluorescence.

Main Components of a Fluorescent Lamp

• Components include the discharge tube, electrodes , and housing.
• The discharge tube is cylindrical, usually made from glass, and consists of two electrodes separated by a gap where electrical discharges happen.
• A type of inert gas, typically argon or neon, fills the tube.
• A modest amount of liquid Mercury is also inside the tube.
• They are often called low pressure mercury-vapor lamps due to the mercury vapor (1 and 5 pascals of pressure).
• The characteristics of the light emitted by the lamp are determined by mercury vapor.
• Inert gas makes it easy to turn and keep the tube's electons under control.
• Each end of a capped tube is an electrode.
• Tungsten electrodes generate an electrical dscharge in the tube, and are typically coated in an electron-emitting material.
• The electrodes are connected to the power supply.
• Tube contains a florescent material, with each florescent compound producing light with different properties.
• The figure shows elements that compose a standard fluorescent lamp.
• Devices have three auxiliaries known as a ballast, condenser, and starter.

Elements of Fluorescent Lamps

• Passing electrical current through each filament inside the tube.
• Filaments get hot and discharge electons to create plasma.
• Plasma then causes the mercury in the tube to evaportate.
• Light materials inside cause the tube to produce elechtromangnetic fields.
• Exterior materials convert the exterior radiation emitted by the fluorescent tube.
• To get the full function of a fluorescent lamp there lamp requires three auxilary elements due to its complexity with auxiliary elements.
• The circuit shown reprents the function of the florescent lamp.
• All lamps reduce the passge of current to avoice the continuous increase of electrical resistance which prevents the lamp from being damaged.
• Balast provides electric current to start the lamp and limits current from passing throguh teh gas.
• The condenser is wired in parralel to the lamp which can compsenate for power issues.
• Starter starts discharge in tube which fills small ampule made of neon in this disopositve.
• The device has condensor placed in parallel.
• The device uses red line voltage to apply voltages to terminals of the electrodes.
• The thermal expansion can produce a small arc and allow current for it to pass.
• IT will break after it is diltated.

Fluorescent Lamp Characteristics

• Larger surface area, producing diffusion that diminishes shine.
• There are characteristics to be measured in flourescent lamps to enumerate the following.
• The light color is a dependent on the fluorescent substance which the lamp contains, as the market has a wide selection of lamps which range from warm to cool.
• There have been lamps that can emit green, red, yellow light.
• Most Common colors are daylight and and whites.
• Index varies from moderate to excellence between temperatures.
• The light output is typically 8 times better than it would be with traditional lamps with the same nominal power, however with the light depreciation and loss of substance the effectiveness will diminish the initial light.

Energy and Fluorescent Lamp Lifespan

• Some energy is transfered to heat and UV radiation but will become visible light.
• The radiant flux is greater from fluorescent lamps than from incandescent lamps.
• Their lighting performace measures between 40-90lm.
• The life span ends and properties or when the electrodes break ends when the filaments break over time.
• Life can be limited due to the constant use of lights.
• The lamp must be replace after 7000 hours of use with minimal light loss and the lamp will continue to function with less light.
• Fluorescents dont produce continuous light and depend on frequency of voltage applied as the lights flicker from this tension.
• The speed occurs fast that you have an illusion that is constant and can cause a stroboscopic effect.

Low pressure sodium vapor lamp

• Electric device that has a low pressure inside the tube.
• Causes discharge and creates monochomatic radiation.
• Process that happend generates violet output visible in electroluminescence.
• The lamp has 2 glass tubes to make the temperature lower.
• The discharge lamp is designed so to improve heat and minimize the lamp.
• The lamp contains a a low pressure neon gas.
• Filament and discharge will have a substance that can emit electrons on both sides of the lamp.
• A ampuole will provide as a thermal barrier to isolate the discharge from the lamp.
• Dependaing on the lamp the power can measure between 390 and 600 in order to produce a tension capable of generating light.
• Autotransfomers are the source of the light.
• Parralel lighting in order to compsenate for power loss in the lamps, whcih happens at a slower production due to its characteristics. The interior generates high light, which gives red.
• The sodium can reach a high point of evaporation and concentration, the light will become red.
• It takes 10 minutes for the light to re emerge as a consistent source and takes 3 mins for it to reheat as a consistent light source.
• Some features in low power lmaps have monochromatic effects that are yellow.

Low pressure vapor lamp Features

• There is an yellow light emitted by these lamps, for the movement and sensitivity which improves visual acuity for the human eye.
• The index for chromatic output is poor.
• There is a lack of color output with temperature on all surfaces as there are not similar qualities to white light in all areas.
• There is a measure of light emitted at 190lm/w.
• About 800 hours of use and at a high rate performance should be revaluated after 1500 hours due to high depreication of luminous.
• This type of lamp works on open roads.
• They are utilized in commercial operations and in some recreational activities.

Luminaires

• Luminaires are equipment that distributes, filters, or transforms the light emitted by one of the lamp.
• In addition, they provide support, protection and connection to the supply network of lamps.
• Luminaires adequately distributed light emitted by the lamp and lead to certain directions, reducing the glare, and high powers.
• In general, luminaires consist of the following.

Parts of Luminaires

• Armor or body, where all components are support.
• Electrical equipment will include access to the source and has auxilirary elements.
• Lamps do not need extra equipment, while discharge lamps have capacitors transformers.
• Reflectors reflect light towards the luminaries .
• Diffusers are light zones for the flow of light.
• Filters enhance or diminish certain characteristitcs of light and power off of radiation emitted.

Interior Lighting Styles

• The design of an interior lighting system includes the number, type, and distribution of luminaires needed to illuminate an enclosed space where some type of activity and lighting adequate illumination can be applied.
• There is a presentation of common interior lightings as well as illuminations.
• Lighting that is calculated that may be appropriate for specific spaces.
• How the light needs to distribute to each space based on the distribution types
• General lighting provides a uniform illumination over the entire area that is illuminated, which is made with uniformal lighting throughout the space used in large spaces.
• General local lighting is situated to give the illumination needed in the space which can increased based on the different illuminations or the type space.
• There is localized lightning with lighting the workspaces , with any general lighting that the space may contain and for some locations.
• This may include machinery in the space.table
• The level of light will vary from room to room

Exterior Lighting

• Exterior lightning must provide needed level through different levels of space through industrial recreational and decoration.
• The part will focus on areas that have lighting.
• The method of lumens is important throughe the value that is calculated
• The formula in this space, is an approach of the illumination methods.
• The lightning can get classfied based on the following
• public roads are where adequate lightning is needed for the safety and transiiton of vehicles and pedestrians in high traffic areas.
• Areas include roads or through a dense commercial areas.
• Industrial areas , are typically construction and power plants.
• The lightning is for sports and recreational outdoor spaces which is an appropraite.
• Decoration to use iluminating structures.