CT30104-Lighting Systems in BuildingsLecture 02

Eng G R Madushan KumaraEng. G.R. Madushan Kumara(BSc. Eng.)

Electron absorbs some energy which causes it Electron absorbs some energy which causes it to “jump” to a higher energy level. This is called excitation.

E2

E1

Energy

N lNucleus

The electron, preferring to be in the lower The electron, preferring to be in the lower energy, immediately drops back down to the lower energy level (de-excitation).

E2 Energy

E1

E2 gy

E1

In order to conserve energy, a photon In order to conserve energy, a photon (discrete bundle of energy) is emitted.

E2 Photon Energy

Photon Energy = E2 – E1E1

Light travels in straight lines.Light travels in straight lines.Light travels much faster than sound.Because of its electric and magnetic Because of its electric and magnetic properties, light is also called electromagnetic radiation.We see things because they reflect light into our eyes.Shadows are formed when light is blocked by an object.

A luminous object is one that produces light.A luminous object is one that produces light.SunLampFireLightning Strike

A l i bj t i th t fl t A non-luminous object is one that reflects light.

MoonMoonReflectorsWalls

Shadows are places where light is “blocked”Shadows are places where light is blocked

Rays of lightRays of light

Light travels through empty space at a speedLight travels through empty space at a speedof 300,000 km/s.At this speed it can go around the world 8 times in one second.

In the 1860s, the Scottish mathematician and In the 1860s, the Scottish mathematician and physicist James Clerk Maxwell succeeded in describing all the basic properties of electricity

d i i f iand magnetism in four equations.This mathematical achievement demonstrated that electric and magnetic forces are really that electric and magnetic forces are really two aspects of the same phenomenon, which we now call electromagnetism.

Newton thought light was in the form of Newton thought light was in the form of little packets of energy called photons and subsequent experiments with blackbody

di i i di i h i l lik radiation indicate it has particle-like propertiesYoung’s Double Slit Experiment indicated Young s Double-Slit Experiment indicated light behaved as a waveLight has a dual personality; it behaves as a Light has a dual personality; it behaves as a stream of particle like photons, but each photon has wavelike properties

Planck’s law relates the energy of a photon to its f l hfrequency or wavelength

E = energy of a photonh = Planck’s constantc = speed of lightλ = wavelength of light

The value of the constant h in this equation, called Planck’s constant, has been shown in laboratory experiments to be.laboratory experiments to be.h = 6.625 x 10–34 J s

A blackbody is a hypothetical object that A blackbody is a hypothetical object that is a perfect absorber of electromagnetic radiation at all wavelengths.Stars closely approximate the behavior of blackbodies, as do other hot, dense objectsobjects.The intensities of radiation emitted at various wavelengths by a blackbody at a various wavelengths by a blackbody at a given temperature are shown by a blackbody curve.

The dominant wavelength at which bl kb d i a blackbody emits

electromagnetic radiation is inversely radiation is inversely proportional to the Kelvin temperature of the object.

The Stefan-Boltzmann law states that a The Stefan Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux E directly

i l h f h f h proportional to the fourth power of the Kelvin temperature T of the object.

E = σT4

The combination of all the allowed The combination of all the allowed transitions produces an emission spectrum for that particular element.No two elements have the same emission spectrum, so the emission spectrum can be used to identify the element in questionused to identify the element in question.

Three Basic Functions.Three Basic Functions.Eyes receive light and generate messages.Visual pathways transmit those messages.Visual centers interpret those messages.

All visual structures are intact at birth th h l i tthough several are immature.For humans most of sensory information is derived via the visual system (eyes)derived via the visual system (eyes).

Human eye

Exposure

•Cornea Iris/pupil •Retina •Brain

ProcessingImage formationExposureControl Detection

•Cornea•Lens

•Iris/pupil•Photoreceptorsensitivity

•Retina•Rods•Cones

•Brain

Why can’t we see immediately after you Why can t we see immediately after you enter a movie theater from daylight?The threshold of detection changes with overall light level.The switch is quite gradual, until the

iti iti f d d t sensitivities of cones and rods cross over at about 7 minutes in the dark.

White light is not a single colour; it is made White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow.Can demonstrate this by splitting white light with a prism.

HueHueValue Intensityy

The name given to a colour.The name given to a colour.

RED YELLOW VIOLET

Pure and basic.Pure and basic.Cannot be made from any other colours.All other colors are made from these.Equal distance from each other on colourwheel.

RED YELLOW BLUE

Made by mixing equal amounts of 2 primary Made by mixing equal amounts of 2 primary colorsFound halfway between the primary hues on the wheel

+ ORANGE+ =

+ = GREEN

+ = VIOLET

Made by mixing equal amounts of adjoining Made by mixing equal amounts of adjoining primary and secondary colors.

A GUIDE TO STUDY HOW TO CHOOSE AND HOW TO CHOOSE AND

COMBINE COLORS

The lightness (Tint) or the darkness (Shade) The lightness (Tint) or the darkness (Shade) of the colour.Tint is adding white to a colour so that it is lighter.Shade is made by adding black to a colour so th t it i d kthat it is darker.

+ =

+

HUE WHITE TINT

+ =

HUE BLACK SHADE

The brightness or dullness of a colorThe brightness or dullness of a color

FUSCHIA - HIGH INTENSITYFUSCHIA HIGH INTENSITYOLIVE - LOW INTENSITY

All colorsWhite

No colorBlack

White + BlackGray

Can be used with most Beige

colors

Appear hot like the sun or like fireAppear hot like the sun or like fireGive feelings of gaiety, activity or cheerfulnessAppear to advance-they make body look largerCan give a nervous impression if overdone

Remind us of water or skyRemind us of water or skyGive feelings of quietness or restfulnessAppear to recede and make body look pp ysmallerCan be depressing if overdone

This is a one-color plan that uses different This is a one color plan that uses different tints, shades and intensities of the color

BLUE

The colour an object appears depends on the The colour an object appears depends on the colours of light it reflects.A red book only reflects red light.

White

lightOnly red light is reflectedlight is reflected

A pair of purple trousers would reflect purple A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue).

M t li htMagenta light

A white hat would reflect all seven colours.A white hat would reflect all seven colours.

White

light

If we look at a coloured object in colouredIf we look at a coloured object in colouredlight we see something different.

Shirt looks red

White

light

Shorts look blue

In different colours of light this kit would In different colours of light this kit would look different.

Red

lightShirt looks red

Shorts look black

Shirt looks blackBlue

light

Shirt looks black

Shorts look blue

Filters can be used to “block” out Filters can be used to block out different colours of light.

Red Filter

Magenta

FilterFilter

The color temperature of a light source is The color temperature of a light source is the temperature of an ideal black body radiator that radiates light of comparable h h f h li h hue to that of the light source.Higher color temperatures over 5000 K are called cool colors (blueish white) but the called cool colors (blueish white), but the lower color temperatures (2,700–3,000 K) are called warm colors (yellowish white through red).

Temperature Source

1,700 K Match flame

1 850 K Candle flame sunset/sunrise1,850 K Candle flame, sunset/sunrise

2,700–3,300 K Incandescent lamps

3,000 K Soft (or Warm) White compact fluorescent lamps

3,200 K Studio lamps, photofloods, etc.

3,350 K Studio "CP" light

4,100–4,150 K Moonlight[, , g

5,000 K Horizon daylight

5,000 KTubular fluorescent lamps or cool

white/daylight compact fluorescent lamps (CFL)fluorescent lamps (CFL)

5,500–6,000 K Vertical daylight, electronic flash

6,200 K Xenon short-arc lamp

6,500 K Daylight, overcast

6,500–10,500 K LCD or CRT screen

15,000–27,000 K Clear blue poleward sky