Let There Be Light[edit]
The first episode shows how the desire, by Greek, Arab and Christian scholars to penetrate the divine nature of light led to modern science's origins.[3] The programme explores the contributions of Empedocles; Euclid; Al Hazen; Roger Bacon; Descartes and Isaac Newton.[4]

Greek scholars[edit]
The nature of light, and how we see, was first investigated by the early Greek philosophers. Light seemed to fill all space while allowing a kind of penetration of the world thus offering a clue to the structure of the whole universe. The world was bathed in light but, to bring it within the world of reason, it was necessary to abstract and choose phenomena where light behaved in a special or strange way: Why do faraway objects appear smaller and why do objects change their position and shape when placed underwater?.[4]

Empedocles' idea, that we see objects because light streams out of our eyes and touches them, became the fundamental basis on which mathematicians would construct some of the most important theories on light and vision. Euclid's Optics expanded this idea to make an important breakthrough: We know in our minds that a faraway building is bigger, yet it is possible to position a finger such that our eye tells us they are of similar size. Euclid's elegant solution was that the eye and both the tops of finger and building must lie on the same line – thus the rays from the eye must follow straight lines; the new discipline of geometry could thus make predictions and solve problems of light and optics.[4]

Al Hazen[edit]
Al Hazen earned a living selling his copies of Euclid's Geometry before obtaining the patronage of Al Hakim, 6th Fatimid Caliph in Cairo. Al Hazen was unable to fulfill his task of stopping the flooding of the Nile and was imprisoned. Here he noted a problem with Empedocles's theory: having been in darkness and then suddenly exposed to light, his eyes felt intense pain. It seemed improbable that, if rays were indeed emitted by the eye, this would happen; instead Al Hazen postulated that light rays travelled through space in straight lines and entered our eyes by bouncing off objects. He studied refraction and the symmetry of reflection, producing a seven-volume work which became the new standard text.[4]

Christian science[edit]
In the centuries following Al Hazen's death, the Catholic Church determined to demonstrate its Divine authority and produce a "Christian" knowledge of light. The translation of the work of the Islamic scholars allowed Roger Bacon, in the 13thC, to study and develop Al Hazen's work through experimentation with the distortion and colour effects of light through glass and water [4]

Lighting or illumination is the deliberate use of light to achieve a practical or aesthetic effect. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting (using windows, skylights, or light shelves) is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants.

Indoor lighting is usually accomplished using light fixtures, and is a key part of interior design. Lighting can also be an intrinsic component of landscape projects.

Fixtures[edit]
Main article: Light fixture
Lighting fixtures come in a wide variety of styles for various functions. The most important functions are as a holder for the light source, to provide directed light and to avoid visual glare. Some are very plain and functional, while some are pieces of art in themselves. Nearly any material can be used, so long as it can tolerate the excess heat and is in keeping with safety codes.

An important property of light fixtures is the luminous efficacy or wall-plug efficiency, meaning the amount of usable light emanating from the fixture per used energy, usually measured in lumen per watt. A fixture using replaceable light sources can also have its efficiency quoted as the percentage of light passed from the "bulb" to the surroundings. The more transparent the lighting fixture is, the higher efficacy. Shading the light will normally decrease efficacy but increase the directionality and the visual comfort probability.

Color temperature for white light sources also affects their use for certain applications. The color temperature of a white light source is the temperature in Kelvin of a theoretical black body emitter that most closely matches the spectral characteristics of the lamp. An incandescent bulb has a color temperature around 2800 to 3000 Kelvin; daylight is around 6400 Kelvin. Lower color temperature lamps have relatively more energy in the yellow and red part of the visible spectrum, while high color temperatures correspond to lamps with more of a blue-white appearance. For critical inspection or color matching tasks, or for retail displays of food and clothing, the color temperature of the lamps will be selected for the best overall lighting effect.

Types[edit]
See also: List of types of lighting

A demonstration of the effects of different kinds of lighting
Lighting is classified by intended use as general, accent, or task lighting, depending largely on the distribution of the light produced by the fixture.

Task lighting is mainly functional and is usually the most concentrated, for purposes such as reading or inspection of materials. For example, reading poor-quality reproductions may require task lighting levels up to 1500 lux (150 footcandles), and some inspection tasks or surgical procedures require even higher levels.
Accent lighting is mainly decorative, intended to highlight pictures, plants, or other elements of interior design or landscaping.
General lighting (sometimes referred to as ambient light) fills in between the two and is intended for general illumination of an area. Indoors, this would be a basic lamp on a table or floor, or a fixture on the ceiling. Outdoors, general lighting for a parking lot may be as low as 10-20 lux (1-2 footcandles) since pedestrians and motorists already used to the dark will need little light for crossing the area.

it_is_the_light wrote on Feb 28^th, 2015 at 7:43pm:

Forms of lighting[edit]
Indoor lighting[edit]

LED Lighting furniture by Manfred Kielnhofer
Forms of lighting include alcove lighting, which like most other uplighting is indirect. This is often done with fluorescent lighting (first available at the 1939 World's Fair) or rope light, occasionally with neon lighting, and recently with LED strip lighting. It is a form of backlighting.

Soffit or close to wall lighting can be general or a decorative wall-wash, sometimes used to bring out texture (like stucco or plaster) on a wall, though this may also show its defects as well. The effect depends heavily on the exact type of lighting source used.

Recessed lighting (often called "pot lights" in Canada, "can lights" or 'high hats" in the US) is popular, with fixtures mounted into the ceiling structure so as to appear flush with it. These downlights can use narrow beam spotlights, or wider-angle floodlights, both of which are bulbs having their own reflectors. There are also downlights with internal reflectors designed to accept common 'A' lamps (light bulbs) which are generally less costly than reflector lamps. Downlights can be incandescent, fluorescent, HID (high intensity discharge) or LED.

Track lighting, invented by Lightolier,[citation needed] was popular at one period of time because it was much easier to install than recessed lighting, and individual fixtures are decorative and can be easily aimed at a wall. It has regained some popularity recently in low-voltage tracks, which often look nothing like their predecessors because they do not have the safety issues that line-voltage systems have, and are therefore less bulky and more ornamental in themselves. A master transformer feeds all of the fixtures on the track or rod with 12 or 24 volts, instead of each light fixture having its own line-to-low voltage transformer. There are traditional spots and floods, as well as other small hanging fixtures. A modified version of this is cable lighting, where lights are hung from or clipped to bare metal cables under tension.

A sconce is a wall-mounted fixture, particularly one that shines up and sometimes down as well. A torchiere is an uplight intended for ambient lighting. It is typically a floor lamp but may be wall-mounted like a sconce.

Street Lights are used to light roadways and walkways at night. Some manufacturers are designing LED and photovoltaic luminaires to provide an energy-efficient alternative to traditional street light fixtures.[6][7][8]


Floodlights are used to illuminate outdoor playing fields or work zones during nighttime.
Floodlights can be used to illuminate outdoor playing fields or work zones during nighttime hours. The most common type of floodlights are metal halide and high pressure sodium lights.

Beacon lights are positioned at the intersection of two roads to aid in navigation.

Sometimes security lighting can be used along roadways in urban areas, or behind homes or commercial facilities. These are extremely bright lights used to deter crime. Security lights may include floodlights.

Entry lights can be used outside to illuminate and signal the entrance to a property.[9] These lights are installed for safety, security, and for decoration.

Underwater accent lighting is also used for koi ponds, fountains, swimming pools and the like.

Vehicle use[edit]
Main article: Automotive lighting
Vehicles typically include headlamps and tail lights. Headlamps are white or selective yellow lights placed in the front of the vehicle, designed to illuminate the upcoming road and to make the vehicle more visible. Many manufactures are turning to LED headlights as an energy-efficient alternative to traditional headlamps.[10] Tail and brake lights are red and emit light to the rear so as to reveal the vehicle's direction of travel to following drivers. White rear-facing reversing lamps indicate that the vehicle's transmission has been placed in the reverse gear, warning anyone behind the vehicle that it is moving backwards, or about to do so. Flashing turn signals on the front, side, and rear of the vehicle indicate an intended change of position or direction. In the late 1950s, some automakers began to use electroluminescent technology to backlight their cars' speedometers and other gauges or to draw attention to logos or other decorative elements.

Lamps[edit]
Main article: Lamp (electrical component)
Commonly called 'light bulbs', lamps are the removable and replaceable part of a light fixture, which converts electrical energy into electromagnetic radiation. While lamps have traditionally been rated and marketed primarily in terms of their power consumption, expressed in watts, proliferation of lighting technology beyond the incandescent light bulb has eliminated the correspondence of wattage to the amount of light produced. For example, a 60 W incandescent light bulb produces about the same amount of light as a 13 W compact fluorescent lamp. Each of these technologies has a different efficacy in converting electrical energy to visible light. Visible light output is typically measured in lumens. This unit only quantifies the visible radiation, and excludes invisible infrared and ultraviolet light. A wax candle produces on the close order of 13 lumens, a 60 watt incandescent lamp makes around 700 lumens, and a 15-watt compact fluorescent lamp produces about 800 lumens, but actual output varies by specific design.[11] Rating and marketing emphasis is shifting away from wattage and towards lumen output, to give the purchaser a directly applicable basis upon which to select a lamp.

On stage and set[edit]
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Main article: Stage lighting

Lighting and shadows

Moving heads in a photo studio set.

Illuminating subject from beneath to achieve a heightened dramatic effect.
Lighting illuminates the performers and artists in a live theatre, dance, or musical performance, and is selected and arranged to create dramatic effects. Stage lighting uses general illumination technology in devices configured for easy adjustment of their output characteristics.[citation needed] The setup of stage lighting is tailored for each scene of each production. Dimmers, colored filters, reflectors, lenses, motorized or manually aimed lamps, and different kinds of flood and spot lights are among the tools used by a stage lighting designer to produce the desired effects. A set of lighting cues are prepared so that the lighting operator can control the lights in step with the performance; complex theatre lighting systems use computer control of lighting instruments.

Motion picture and television production use many of the same tools and methods of stage lighting. Especially in the early days of these industries, very high light levels were required and heat produced by lighting equipment presented substantial challenges. Modern cameras require less light, and modern light sources emit less heat.

Light exposure[edit]
Typical measurements of light have used a Dosimeter. Dosimeters measure an individual's or an object's exposure to something in the environment, such as light dosimeters and ultraviolet dosimeters.

In order to specifically measure the amount of light entering the eye, personal circadian light meter called the Daysimeter has been developed.[21] This is the first device created to accurately measure and characterize light (intensity, spectrum, timing, and duration) entering the eye that affects the human body's clock.

The small, head-mounted device measures an individual's daily rest and activity patterns, as well as exposure to short-wavelength light that stimulates the circadian system. The device measures activity and light together at regular time intervals and electronically stores and logs its operating temperature. The Daysimeter can gather data for up to 30 days for analysis.[22]