Physical Processes Employed in the artificial sources

• 1. Incandescence - Thermo luminescence is by definition radiation at high temperature. The sources employing this process are Incandescent Lamp, Gas Lamp, (flames and in oil Lamps and wax candles). They lead to a continuous spectrum of radiation.

• 2. Luminescence -Luminescence Electro luminescence by definition Chemical or Electrical Action on gases or vapour radiation. Here colour of radiation depends on the material employed. Usually this process leads to Line or Band Spectrum.

• 3. Fluorescence - Fluorescence is a process in which radiation is absorbed at one wavelength and radiated at another wavelength e.g.UV impinging on Uranium – Fluorescent oils. This re radiation makes the light radiated visible.

• 4. Phosphorescence - Phosphorescence is a process when energy is absorbed at some time and radiated later as glow. Examples of this process are Luminous paints that contain calcium sulphide that lead to Phosphorescence. They produce light Radiation after exposure to light.

In practice good efficient lighting is obtained by combining Luminescence and Fluorescence. Fluorescent lamp is Luminescent source of low luminous value activating Fluorescent surfaces which lead to visible radiation. Here intensity depends on gas or vapour involved and phosphor material. However, the temperature of the material play a role in radiation.

Visible light is light that the human eye can perceive. When you look at the sun's visible light, it appears to be colourless, which we call white. Although we can see this light, white isn't considered part of the visible spectrum. That's because white light isn't the light of a single colour but instead many colours.

Visual tasks•  The visual system carries out a number of complex tasks,

including the reception of light and the formation of monocular representations.

• The build up of a binocular perception from a pair of two dimensional projections.

• The identification and categorization of visual objects.• Assessing distances to and between objects and guiding body

movements in relation to visual objects.• The psychological process of visual information is known

as visual perception, a lack of which is called blindness. • Non-image forming visual functions, independent of visual

perception, include the pupillary light reflex(PLR) and circadian photoentrainment.

• Eye acquires > 80% information acquired by human.

• An Eye comprises of Iris, Focusing Lens and Retina. It

Resembles – a Camera in general structure and action.

Eye Camera

Iris Lens

Retina

Shutter Lens

Film

Ciliary BodyA structure located behind the iris (rarely visible) which produces aqueous fluid that fills the front part of the eye and thus maintains the eye pressure. It also allows focusing of the lens.

ConjunctivaA thin lining over the sclera, or white part of the eye. This also lines the inside of the eyelids. Cell in the conjunctiva produce mucous, which helps to lubricate the eye.

CorneaThe transparent, outer "window" and primary focusing element of the eye. The outer layer of the cornea is known as epithelium. Its main job is to protect the eye. The epithelium is made up of transparent cells that have the ability to regenerate quickly. The inner layer of the cornea is also made up of transparent tissue, which allows light to pass.

IrisInside the anterior chamber is the iris. This is the part of the eye which is responsible for one‘s eye colour. It acts like the diaphragm of a camera, dilating and constricting the pupil to allow more or less light into the eye.

PupilThe dark opening in the centre of the colored iris that controls how much light enters the eye. The colored iris functions like the iris of a camera, opening and closing, to control the amount of light entering through the pupil.

LensThe part of the eye immediately behind the iris that performs delicate focusing of light rays upon the retina. In persons under 40, the lens is soft and pliable, allowing for fine focusing from a wide variety of distances. For individuals over 40, the lens begins to become less pliable, making focusing upon objects near to the eye more difficult. This is known as presbyopia.

Retina The membrane lining the back of the eye that contains photoreceptor cells. These photoreceptor nerve cells react to the presence and intensity of light by sending an impulse to the brain via the optic nerve. In the brain, the multitude of nerve impulses received from the photoreceptor cells in the retina are assimilated into an image.

Optic NerveThe optic nerve is the structure which takes the information from the retina as electrical signals and delivers it to the brain where this information is interpreted as a visual image. The optic nerve consists of a bundle of about one million nerve fibers.

Laws of illumination

Colour theory

• Newton thought that colours were a sensory experience, rather than a property of light.

• Newton’s theory of colour was that the sun’s light, or any other white light, was a mixture of rays of light, each with its own refrangibility, by which he meant characteristic angle of refraction in a prism.

• What is a colour: when we look at a scene, our visual nerves register colour in terms of the attributes of colour the amount of green-or-red; the amount of blue-or-yellow; and the brightness.

Colour nerves sense green or red — but never both; and Blue or yellow — but never both.

Thus, we never see bluish-yellows or reddish-greens. The opposition of these colours forms the basis of colour vision.

Ewald Hering (1834-1918) devised the first accurate theory of colour vision.

A modern representation of colour space. This is conceptually similar to Hering’s circles, but the middle fades to gray.

• Modern colour theory is based on three primary colours red, green and blue.

• Also warm and cool colours has been important since at least the late 18th century used in design practices today

• Colour theory has described perceptual and psychological effects as

Warm colours are said to advance or appear more active in a painting, warm colours are said to arouse or stimulate the viewer.

while cool colours tend to recede used in interior design or fashion, also cool colours calm and relax.

Additive colour

• Additive colour synthesis is the creation of colour by mixing colours of light. Human vision relies on light sensitive cells in the retina of the eye. There are two basic kinds of sensors. These are rods and cones.

• Rods are cells which can work at very low intensity, but cannot resolve sharp images or colour.

• Cones are cells that can resolve sharp images and colour, but require much higher light levels to work.

• The combined information from these sensors is sent to the brain and enables us to see.

• There are three types of cone. Red cones are sensitive to red light, green cones are sensitive to green light, and blue cones are sensitive to blue light. The perception of colour depends on an imbalance between the stimulation level of the different cell types.

• Additive colour processes, by having the capability to generate an image composed of red, green, and blue light.

• Since the intensity information for each of the three colours is preserved, the image colour is preserved as well.

• The spectral distribution of the image will probably be wrong, but if the degree of intensity for each of the primary colours is correct, the image will appear to be in right colour.

The three primaries in light are red, blue, and green, because they correspond to the red, green, and blue cones in the eye.

Red + Green = YellowRed + Blue = MagentaGreen + Blue = CyanComputer monitors and televisions are the most common examples of additive colour.

Subtractive colour • When learning basic colour theory, art students typically use

familiar colours like red, yellow, and blue.• The most frequently used primary colours for subtractive

colour mixing are cyan, magenta and yellow.• Subtractive colour mixing is employed with paints and

pigments, in contrast with additive colour mixing with coloured lights for spotlighting and theatrical lighting.

• Subtractive colour processes work by blocking out parts of the spectrum. The idea of subtractive colour is to reduce the amount of undesired colour reaching the eye.

• The three primaries on the artist’s colour wheel are red, blue, and yellow.

• Yellow light is observed when all blue light is removed from white light, magenta forms when green is removed, and cyan is produced when red is removed.

• If, for example, you had a yellow image, you would want to have a dye that would let red and green reach the eye, and block out blue. The additive secondaries become subtractive primaries, because each of the additive secondaries will reflect two of the additive primaries, and absorb one of the additive primaries.

• White cannot be produced by any combination of the primary subtractive colours, which is the main reason that no mixture of coloured paints or inks can be used to print white.

When all three primary subtractive colors are added, the three primary additive colors are removed from white light, leaving black (the absence of any color).

UNIT - II

Innovation in lighting has brought new products and

classifications to the home, office and industrial. Lighting classifications include indoor and outdoor lights

with entirely different purposes. Street and highway lighting can be low-pressure sodium

that has poor colour rendition and that takes 10 minutes to

illuminate. Stadium lights, Emergency lighting,

Photographic lighting etc.,

Natural: Sunlight, candlelight and firelight; this is light

that moves and is sometimes referred to as kinetic.

Artificial: Incandescent Fluorescent LEDHigh Intensity DischargeOutdoor Solar

Broad classification of light

• An incandescent bulb uses heat caused by an electrical current.

• When electrical current passes through a wire, it causes the wire to heat. The wire, or filament, gets so hot that it glows and gives off light.

• Everyday incandescent light bulbs have a filament made of tungsten. Since the hot tungsten would quickly burn away if it were exposed to oxygen, it must be placed in a sealed glass bulb which is either evacuated or filled with a gas that wont let it burn.

• Because of their inefficiency, incandescent light bulbs are gradually being replaced in many applications by other types of electric lights, such as fluorescent lamps, compact fluorescent lamps (CFL) etc.,

• Fluorescent lamp produces white light.• The average life is 7500 hours.• The light output is 70 lumens per watt.• They have poor rendering especially for red colour.

• Light-emitting diodes (LED) are semiconductors. As electrons pass through this type of semiconductor, it turns into light.

• Compared to incandescent and CFL bulbs, LED lights are more efficient at turning energy into light.

• Therefore, less of the energy radiates from the bulb as heat. This is why LED bulbs are cooler during operation than incandescent and CFL bulbs.

• As the light-emitting diodes create light, they warm up quite a bit for their size. LEDs are heat sensitive, so it's important that the heat move away so that it doesn't damage the semiconductors.

• In order to do this, these lights need a system to keep cool. Most LED lights have a heat sink plate that moves the heat away from the light-emitting diodes through the heat sink plate.

Classification of light in Decoration

• Ambient: A hidden source of light that washes a room with a glow. It flattens an interior and creates very little shadow.

• Accent: Directional lighting or lighting that adds interest or highlights a certain object or unusual architectural feature in a room.

• Task: Task lighting is just that; lighting that's used to perform daily activities such as reading, cooking, shaving, putting on makeup, etc. It needs to be glare-free.

• Aesthetic: Lighting itself can be a work of art. A neon sculpture would be purely decorative and an example of aesthetic lighting.

• Tungsten: Gives off a slightly yellow tinge. These are ordinary light bulbs.

• Spotlight: Gives a focused burst of white light.• Halogen: Gives the closest approximation of natural

daylight, known as "white light." colours appear sharper under halogen light. The halogen bulb is also an energy saver. Can be dimmed.

• Fluorescent: The typical fluorescent gives a flat, cold light, often bluish and harsh. It is a daylight-equivalent

and cannot be put on a dimmer.

A spectral energy distribution (SED) is a plot of brightness

or flux density versus frequency or wavelength of light.

It is used in many branches of astronomy to characterize

astronomical sources. Galaxies emit electromagnetic radiation over the full possible

frequency/wavelength range. Analysis of these radiations is the

main means through which astronomers study the distant

galaxies and thus learns about their formation and evolution. The

distribution of energy over wavelength/frequency is called the

spectral Energy Distribution.

Spectral Energy Distribution

• A spectral energy distribution (SED) is a graph of the energy emitted by an object as a function of different wavelengths.

• The graph is a typical curve, called a blackbody curve. It shows that the amount of energy emitted by the object at all wavelengths varies with the temperature of the object.

• Hotter objects emit more light at shorter wavelengths than cooler objects; therefore the hotter the object, the more the peak wavelength is shifted toward the left of the graph.

• Stars aren’t really blackbodies but the emission from them is very similar to blackbodies. We can "fit" a blackbody curve to the star.

Luminous efficacy

Luminous efficacy is a measure of how well a light source

produces visible light. It is the ratio of luminous flux to power.

Depending on context, the power can be either the radiant

flux of the source's output, or it can be the total power

(electric power, chemical energy, or others) consumed by the

source.

Luminous efficiency:• The effectiveness of illumination (luminous efficiency) is

defined by the ratio of the luminous flux emitted by a specific source of light and the energy consumed by it in a time unit.

• The unit: lumen/watt (lm/W)Examples of luminous efficiency of various light sources:

light bulb: 8-10 lm/Whalogen lamp: 16 lm/Wfluorescent lamp: 45-104 lm/Wwhite LED: 26-100 lm/Wmetal halide lamp: 85-115 lm/Whigh pressure sodium lamp: 150 lm/W low pressure sodium lamp: 200 lm/W

Colour temperature

The colour temperature of a light source is the

temperature of an ideal black body radiator that radiates light

of comparable hue to that of the light source. In practice,

colour temperature is only meaningful for light sources

that do in fact correspond somewhat closely to the radiation of

some black body.

Colour temperatures over 5,000K are called cool

colours (bluish white), while lower colour temperatures

(2,700–3,000 K) are called warm colours (yellowish white

through red)

Colour temperature applicationsLightingAquacultureDigital photographyPhotographic filmDesktop publishingTV, video, and digital still camerasArtistic application via control of colour temperature

Lighting: For lighting building interiors, it is often important to take into account the colour temperature of illumination.

Aquaculture: In fishkeeping, colour temperature has different functions and foci, for different branches.

In freshwater aquaria, colour temperature is generally of concern only for producing a more attractive display. In a saltwater/reef aquarium, colour temperature is an essential part of tank health.

Digital photography:In digital photography, colour temperature is sometimes used interchangeably with white balance, which allow a remapping of colour values to simulate variations in ambient colour temperature

• Photographic film: Photographic emulsion film sometimes appears to exaggerate the colour of the light, as it does not adapt to lighting colour as human visual perception does.

• Desktop publishing: In the desktop publishing industry, it is important to know a monitor’s colour temperature. Colour matching software, such as coloursync will measure a monitor's colour temperature and then adjust its settings accordingly.

Colour rendering index

• Colour rendering relates to the way objects appear under a given light source. The measure is called the "colour rendering index", or CRI.

• A low CRI indicates than objects may appear unnatural under the source, while a light with a high CRI rating will allow an object's colours to appear more natural.

• For lights with a "warm" colour temperature the reference point is an incandescent light. For lights with a cool colour temperature the reference is sunlight.