Credits to : Dr. R K Ludam. the ppt is already available on slide share, but uploading as a part of complete syllabyus

1. LIGHT
Dr R.K.Ludam
Dept Of Community Medicine
V.S.S.M.C.H Burla

2. Introduction-:
• Good Lighting is essential for effective vision and puts
lesser strain increasing working efficiency.
• Light Factors-:
- Sufficiency
- Distribution
- Absence of Glare
- Absence of Sharp Shadows
- Steadiness
- Colour Of Light
- Surroundings.

3. 1.Sufficiency-: Should be sufficient enough to enable the
eye to discern the details of the object as well as the
surroundings.
- Illumination of 15-20 foot candles is a basic minimum
- may differ from 5-100 foot candles in industries
2.Distribution-: should be uniform, having same intensity,
over the whole field of work.
3. Absence of Glare-: Glare is excessive contrast which may
be direct from a light source or a Reflected glare,
- it causes acute discomfort and reduces critical vision.
4.Absence of Sharp Shadows-: it causes confusion to the
eye
5.Steadiness-: source should be constant to avoid eye
strain

4. 6.Colour of Light-: is not very important as long as the
intensity is adequate.
- It should be soothing to the eyes.
7. Surroundings-: For effective vision ,colour schemes in
the room are important.
- e.g.-Black object is difficult to identify in a dark
background
- so Reflection Factors Are as follows-:
Ceiling and Roofs - 80%
Walls - 50 – 60%
Furniture - 30 – 40%
Floor - < 15 – 20%
- Contrast colours can be used to prevent accidents

5. Light Measurement Units

6. Natural Lighting-:
• Derived partly from the sky and partly from reflection
• It also depends upon the time of the day, season,
weather and atmospheric pollution.
Suggestions For Improving Daylight Illumination-:
(1) ORIENTATION-:The brightness of the sky is not constant
on the east and west and therefore the illumination is
subject to variation in buildings facing east or west.
- Buildings are therefore oriented, wherever possible,
towards north or south for uniform illumination.
- This is particularly important in respect of schools,
factories and laboratories where uniform lighting is
required in all the rooms.

7. 2) REMOVAL OF OBSTRUCTIONS-: Removal of obstructive
items either wholly or partially is likely to give the most
effective single improvement in lighting.
3) WINDOWS-: Windows should be properly planned
- A tall window gives greater penetration of light; a broad
window gives greater diffusion of light.
- The rule is that window area should not be less than 10%
of the floor area.
- The usefulness of the windows is reduced, by covering
them unnecessarily with curtains and screens.
4) INTERIOR OF THE ROOMS-: The ceiling should be white,
the upper portions of the walls light tinted; and lower
portions somewhat darker so as to give comfortable
contrast to the eyes

8. • Measurement of Day Light-:
DAYLIGHT FACTOR (D.E) It is the ratio of illumination,
given point to illumination at a point exposed
simultaneously, to the whole hemisphere of the sky
(taken as 500 foot candles) excluding direct sunlight.
Instantaneous Illumination INDOORS
D.F = ×100
Simultaneously Occurring Illumination OUTDOORS
- it is recommended that in living rooms the daylight factor
should be at least 8 per cent and in kitchens about 10
per cent

9. • Artificial Lighting-: There are five systems of artificial
lighting direct,semi-direct,indirec,semi –indirect, direct-
indirect.
A)Direct-: In direct lighting 90 to 100 per cent of the Iight is
projected directly towards the working area.
- Direct lighting is efficient, economical. But tend to cast sharp
shadows.
- It should not fall into the eyes.
B)Semi Direct-: Here 10 to 40 % of the light is projected
upwards so that it is reflected back on the object by the
ceiling.
C)Indirect-: light does not strike a surface directly. because 90 to
100 per cent of the light is projected towards the ceiling and
walls.

10. 4)Semi Indirect-: Here , 60 to 90% of the light is directed
upwards, and the rest downwards.
(5) Direct Indirect-:Here , light is distributed equally.
Methods of Artificial Lighting-:
A)Filaments Lamp-: The electric current heats up the tungsten
filament and the light emitted depends upon the
temperature.
• Accumulation of dust on the bulbs reduces illumination by
30 to 40 per cent.
• B)Fluoroscent Lamp-: Fluorescent lamps are economical in
the use of electric current; they are cool and efficient; the
light emitted simulates natural light.

11. • The lamps consist of a glass tube filled with mercury
vapour and an electrode fitted at each end. The inside
of the tube is coated with fluorescent chemicals, which
absorb practically all the ultraviolet radiation and remit
the radiation in the visible range.
• The total emission of energy from two lamps is as
follows-:
Light Heat
Filament 5% 95%
Fluoroscent 21% 79%

12. Lighting Standards

13. Effect of light pollution
• Human health
 Exposure to light at night suppresses the production
of hormone, melatonin which is synthesized in the
brain’s pineal gland only when the eye signal it is dark.
 Melatonin has several beneficial effect. It boosts the
immune system, lowers cholesterol. Protects the
body’s cardiovascular system, stabilize the biological
rhythm and restore the night cycle of rest and repair
in its absence, a person suffer from chronic fatigue

14. Effect On Flora & Fauna
• Lightning from high-rise office buildings confuses migratory
birds. The avian crash into the buildings and die.
• Artificial light along the sea beaches confuses baby turtle.
• The nocturnal frog are blinded by even dim light. Their ability to
hunt is drastically reduced.
• Outdoor lighting causes a significant decline in the population of
moth by exposing them to predators. It also disturb the flight,
vision, migration and feeding habits of moths.
• Night blooming flower depend on nocturnal insect for
pollination.
• Light pollution around lakes prevent zoo plankton like daphnia
from consuming surface algae. This causes the algae colonies to
bloom.