Light - Session 4

Light

Session 4

Light - Session 4

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390

to 700 nm

Visible Light

Light - Session 4

Ultraviolet light is a form of radiation which is not visible to the human eye. It’s in an invisible part of the “electromagnetic spectrum”. Radiated energy, or radiation, is given off by many objects: a light bulb, a crackling fire, and stars are some

examples of objects which emit radiation.

Black Light

Light - Session 4

Black Light

If you turn on a black light bulb in a dark room, what you can see from the bulb is a purplish glow. What you cannot see is the ultraviolet light that the bulb is also producing.

What you see glowing under a black light are phosphors.

Phosphors are materials that exhibit the phenomenon of luminescence, i.e. they emit light when exposed to radiation such as ultraviolet light or an electron beam.

A phosphor converts the energy in the UV radiation from a black light into visible light.

Light - Session 4

Luminescence

Luminescence is the emission of lighting by a substance not resulting from heat. It is a form of cold body radiation. It can be caused by chemical reactions, subatomic motions or stress on a crystal.

Examples of luminescence are bioluminescence, fluorescence and phosporenscence.

Light - Session 4

BioluminescenceBioluminescence is the biochemical emission of light by living organisms such as

glow-worms, deep sea fish, fire-flies

Some call it ‘living light’, all bioluminescent organisms use a reaction between an enzyme and a substrate to make light, but different species use different chemicals in the process

Light - Session 4

FluorescenceFluorescence is the emission of light by a substance that has absorbed light or

other electromagnetic radiation.

It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation.

Light - Session 4

Phosporenscencephosphorescence is a process in which energy absorbed by a substance is released relatively slowly in the form of light. This is in some cases the mechanism used for “glow-in-the-dark”

materials which are “charged” by exposure to light.

Phosphorescent materials “store” absorbed energy for a longer time, as the processes required to re-emit energy occur less often.

The study of phosphorescent materials led to the discovery of radioactivity in 1896.

Light - Session 4

Light

and Lamps

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Incandescent Lamp

An incandescent lamp is an electric light which produces light with a filament wire heated to a high temperature by an electric current passing through it until it glow.

The hot filamt is protected from oxidation with a glass bulb that is filled with gas.

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Tungsten Halogen

The tungsten halogen lamp is an advanced form of the incandescent lamp.

The halogen lamp has a tungsten filament similar to the standard incandescent lamp, however the lamp is much smaller for the same wattage, and contains a halogen gas in the bulb. The halogen is

important in that is stops the blackening and slows the thinning of the tungsten filament.

This lengthens the life of the bulb and allows the tungsten to safely reach higher temperatures (therefore makes more light).

Light - Session 4

Fluorescent Lamp

An electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow.

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Electrons - a negative elementary electric charge.

Electrodes - a conductor through which electricity enters or leaves an object, substance, or region.

Argon Gas (merucry Vapour) - is a chemical element

A fluorescent lamp converts electrical energy into useful light much more efficiently than incan-descent lamps.

Light - Session 4

LED - Light Emitting Diode

If you turn on a black light bulb in a dark room, what you can see from the bulb is a purplish glow. What you cannot see is the ultraviolet light that the bulb is also producing.

A Diode is a semiconductor device with two terminals. Typically allowing the flow of current in one direction only, having two electrodes (an anode and a cathode).

Light - Session 4

LED - Light Emitting Diode

The Die emits blue light and is coated with phosphor that absorbs a portion of the blue light and re-emits it as other colour to fill in the spectrum resulting in white light.

A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence

Light - Session 4

LED - Light Emitting DiodeWhy are they so good?

LEDs are said to be the most efficient hwhite light source ;

Smalled light source availableMercury & Lead - free from toxic chemicals

Energy efficientLifetime

No UV emissions and little Infrared

Light - Session 4

Quality Assurance

How do we know what a good light source is?

What qualities does it need?

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Correlated Colour Temperature

Correlated colour temperature (CCT) is a measure of light source color appearance defined by the proximity of the light source’s chromaticity coordinates to the blackbody locus, as a single number

rather than the two required to specify a chromaticity.

Light - Session 4

BlackBody Locus (Planckian Locus)

is the path or locus that the color of an incandescent black body would take in a particular chromaticity space as the blackbody temperature changes. It goes from deep red at low

temperatures through orange, yellowish white, white, and finally bluish white at very high tempera-

Chromaticity is an objective specification of the quality of a color regardless of its luminance. Chromaticity consists of two independent parameters, often specified as hue and colorfulness,

where the latter is alternatively called saturation, chroma, intensity, or excitation purity. This number of parameters follows from trichromacy of vision of most humans, which is assumed

by most models in color science.

Light - Session 4

ChromaticityChromaticity is an objective specification of the quality of a color regardless of its luminance.

Chromaticity consists of two independent parameters, often specified as hue and colorfulness,

where the latter is alternatively called saturation, chroma, intensity, or excitation purity. This number of parameters follows from trichromacy of vision of most humans, which is assumed

by most models in color science.

Light - Session 4

Colour Rendering IndexThe Colour Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a “given”

light source is at rendering colour when compared to a “reference” light source. The higher the CRI, the better the colour rendering ability.

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Colour Rendering Index

2700-3200k 4000-4500k 5000-6500k

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Colour Rendering Index at.....Is the SI base unit of thermodynamic temperature, equal in magnitude to the degree Celsius.

SI Base Unit - The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units are derived.

The SI base units and their physical quantities are: metre for length. kilogram for mass, kelvin for temperature

Light - Session 4

Binning LED components vary from each other during production. Their difference can manifest in color, forward voltage, and flux. The binning practice has been designed to maximize effective utilization in the production of LEDs. Even within the same production batch, LEDs will be prone to quite large

Each LED manufacturing brand divides LEDs by different standards and therefore has different bin-ning, but because very often product lines are developed for similar purposes, binning of different

brands is never far apart.

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Precedent Artist

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James TurrellRoden Crater, Northern Arizona

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“My desire is to set up a situa-tion to which I take you and let

you see.

It becomes your experience.”

James Turrell - Roden Crater

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Light - Session 4

https://vimeo.com/67926427

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James Turrell - Skyspace

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James Turrell - Deepsky

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Somerset House Biennale

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Somerset House Biennale

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Somerset House Biennale

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Somerset House Biennale

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Somerset House Biennale

Thirty seven countries and territories from six continents are presenting newly monumental installations and commissioned works exploring the theme Utopia by Design in the first London Design Biennale.