LIGHTINGLIGHTING

LIGHT

What ?

How ?

Why ?

Units of measurement

No description Quantity measured Name

recommended unit

Other units

1 Brightness of point source

Luminous intensity

Candela Candle power

2 Flow of light Luminous flux Lumen Foot candle

3 Amount of light reaching surface

Illumination or illuminance

Lux Lumen/cm2

(Phot)

4 Amount of light re-emitted by surface

Brightness or luminance

lambert Foot Lambert Candles/cm2

Requirements for good lighting

Sufficiency

Distribution

Absence of glare

Absence of sharp shadows

Steadiness

Colour of light

Surroundings

Lighting standards

Illumination range – 0.1 lux to 100,000 lux

Vision against illumination follows a curve

30 times higher than the minimum required

Illuminating engineer society

Visual task Illumination (lux)

Casual reading 100

General office work 400

Fine assembly 900

Very severe tasks 1,300 - 2,000

Watch-making 2,000 - 3,000

sources

Production of light

Thermo luminance

Chemo luminance

Phosphorescence

Cathodoluminescence

Natural

Direct or reflected

Design, Orientation, location, surroundings.

Time, season, weather & pollution

Measuring Daylight

Daylight factor (D F)

D F = instantaneous illumination indoor x 100

simultaneously occurring illumination outdoor

Daylight factor meter

Living room 8 %

Kitchen 10%

Improving daylight illumination

Orientation

Removal of obstacles

Windows

Interior

Artificial

Types

Direct

Semi-direct

Indirect

Semi-indirect

Direct - indirect

Filament lamps

Tungsten filament

Light depends on temperature

5 % light

Dust – illumination by 30 to 40 %

Florescent lamps

Similar to natural light

21 % light

Glass tube, mercury vapour, & electrode

fluorescent chemical coating – absorbs all UV

LED lamps

Long-lasting -up to 10 times

Durable -do not have a filament, they are solid

Cool- LEDs produce 3.4 btu's/hour, compared to

85 for incandescent bulbs

Mercury-free

More efficient - 2-17 watts

Cost-effective

Light for remote areas and portable generators