Light

INTRODUCTION
 Essential for efficient vision
 Imperfect light cause ill health
 Imperfect light damage the eyesight and produce physical and mental
discomfort
 Visible light has wave length of electromagnetic waves from 380nm to
760nm

MEASUREMENT OF LIGHT
 Measurement of lighting includes the foot-candle and lumen type. The four
measurements of lights are as follows:
 Luminous intensity or power of artificial light is measured by the standard
“Candle”
 Amount of light given off by burning wax candle is 120grains/hour is
called candle power
 Illumination received from 1 candle at a distance of 30.48 cm known as
10.76 lux
 The illumination is measured by instrument called photometer. The light is
measured by other parameter such as:
 Luminous flux(flow of light)expressed in lumens
 Illumination(amount of light reaching a surface)
 Luminance( brightness i.e., amount of light reflected from a surface)

ESSENTIAL OF GOOD LIGHTING
 Sufficiency and uniformity in distribution
 Absence of Glare
 Sharp shadow is disturbing and also it should not be patchy , as it can lead
to accident
 Over bright Light

SOURCES OF LIGHT
NATURAL
• Sun
ARTIFICIAL
•Lasers Electric Welding
•Carbon Arc
•Tungsten filament lamps
•Fluorescent lamps

NATURAL LIGHT
 It is obtained not only from sky but also from reflection
 It depends on time of day , season, weather and Atmospheric pollution
 It is better and cheaper than Artificial light
 It depends upon design , orientation , location , type and size of house
 North and south facing house gives uniform illumination and white
washing gives good light
 MINIMUM AREA FOR WINDOWS OR DOORS
 Living and bedrooms:1/10 of the total room area
 School room:1/5 of the total room area
 Factory : 1/5 of total room area
 Cow shed:1/5 of total room area

ARTIFICIAL LIGHT
 Best form of artificial lighting is electric tube light
 Gas lighting either coal gas or acetylene , or petrol gas is liable to pollute
air with carbon monoxide
 Living room: 75.35 lux
 Stairs : 21.5 -43.05 lux
 Class & library room: 107.64 lux
 Hotel : 64.58 lux
 Office general: 107.64 lux
 Hospital ward : 32.29 lux
 Industrial processes: 59.20 lux
 Operation theater: 1076.39 lux

FACTORS AFFECTING GOOD LIGHTING
 Sufficiency ( Illumination OF 161.45- 215.27 Lux)
 Distribution( uniform Light with same intensity)
 Absence of Glare
 Absence of Sharp Shadows( Slight shadows are inevitable, sharp
contrasting shadows are disturbing)
 Steadiness ( Constant source of light without flickering)
 Color of Light ( Artificial light has to approximate with day light color)
 Surroundings ( Ceilings and roof should have a reflection factor of 80%,
contrasting colors to prevent accidents in culverts , bridges)

UNITS OF LIGHT
 LUMINOUS INTENSITY : It is the power of a light source considered as
a point radiating in all directions, measured as Candelas
 LUMINOUS FLUX: It is the flow of light related to unit of solid angle
measured in Lumens
 ILLUMINANCE: It is the amount of light reaching a surface measure in
lux /unit area
 LUMINANACE: It is the amount of light reflected from a surface
measured in Lamberts

Measurement of Light with UNITS
Luminous Intensity
(CANDELA)
Luminous Flow
(LUMEN)
Illumination
(LUX)
Luminance
(LAMBERT)

METHODS OF IMPROVE LIGHTING
 1. NATURAL ILLUMINATION
a) Natural lighting
 Building faced north and South will ensure uniform light at morning to
evening
 tall narrow window gives greater penetration of light and a broad window
gives greater diffusion of light
 Interior of room with white ceiling , with upper portion of walls to be light
colored, lower portion dark tint
 Proper interior, design and orientation of building: placement of windows,
skylight reflection and penetration and doorways.

 Orientation: brightness of sky is not constant on east & west and therefore
the illumination is subject to variation in building east or west.
 Removal of Obstruction : whole or partial removal of obstruction is the
most effective single improvement in lighting
 Windows : Tall window ensure greater diffusion of light. Window area is
correlated to the purpose the room is intended to serve . It also penetrate
more light in rooms, but broader windows diffuse more light.
 Interior of the Rooms : Day light illumination is liable to change from
moment to moment; its not measured in terms of foot candles. Re-liance is
placed on a factor called daylight factor.(DF)
DF = Instantaneous illumination indoors X 100
Simultaneously occurring illumination outdoors

Advantages of having natural light:
 Reduces bilirubin level in case of premature infants having
hyperbilirubinemia
 Maintains the biological rhythm of body
 Stimulates melanin synthesis
 Activate the precursors of Vitamin D
 Maintain the adrenocortical Secretion.

2. ARTIFICIAL ILLUMINATION
 Artificial Lighting:
Artificial light can be produced by using tungsten filaments , lamps or
fluorescent lamps . Even lasers and electric weldings or carbon can
produce artificial light.
Depending on the type of projection of light towards working area, or
upwards or downward and of reflection basis, it is divided into 5 types:
 Direct Lighting
 Semi - direct Lighting
 Indirect Lighting
 Semi - indirect Lighting
 Direct & Indirect lighting

Electric light is the method of providing artificial illumination . The
different types of electric lights are:
 Filament Lamps
 Fluorescent Lamps
 Emission of energy by Lamps:
Lamps Light(%) Heat(%)
Filament 5 95
Fluorescent 21 79

Different types of Fluorescent lamps are:
 Neon-filled sodium discharge lamp
 Mercury vapor lamp
 Cold cathode neon lamp
 Shadowless light
Other sources of artificial light are:
1. Gas light
2. Gas burner

STANDARDS OF LIGHTING
 Eye responds to a range of illumination ranging from 0.1(full moon light )
to 100000 lux (bright sunshine)
 The illumination level should be 30 times higher than the level at which
the task can just be done.
 For practical situations and various activities, the following values have
suggested by the illuminating engineering society:
 Visual task :Illumination
 Casual Reading:100
 General office work: 400
 Fine Assembly:900
 Very severe task:1300-2000
 Watch making: 2000-3000

CRITERIA FOR GOOD
LIGHTING
1.Proper Illumination
 For satisfactory vision Minimum requirement of 161.45 -215.27 lux is
required
 Stairs:53.81 lux
 Corridors:1076.39 lux
2. Uniform distribution
 Light Fall over the whole or the area of work with same intensity.
3. Not too bright light
Bright light cause constriction of pupils & more strain to eye where as with
glare light one will be unable to visualize the object.
4. Absence of flickering
It creates eye strain

5. No sharp or contrast shadows:
 It cause confusion and should not be present in field of vision
6. Too bright light
 It injure the eye through photochemical reaction in retina, blue light injury
may occur with sustained exposure exceeding 0.1mW/cm2 and retina may
burn with prolonged exposure to 10W/cm2.
7. Too light illumination:
 Eye strain and seasonal affective disorders
8.Thermal effects of light:
 Too much heat cause injury to iris , lens, cornea & skin due to exposure to
laser radiation

POOR LIGHTING
 Eye strain
 Annoyance
 Discomfort
 Accidents
 Injury to eye
 Retinal burn

PREVENTION OF EFFECTS OF POOR LIGHTING
 Proper illumination
 Appropriate training
 Proper design of buildings
 Proper design of equipments
 Protective eye shield
 Not to look to the source of light
 Avoid looking directly to high intensity sources such as laser or Carbon arc
 Proper planning of town

Light

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