5. Measurement of light
Luminous intensity: power of a light source
measured as candelas
Luminous flux : flow of light (lumen)
Illumination : amount of light
reaching surface in lux
Brightness : amount of light reflected
from surface (lamberts)
6. Natural lighting
Orientation: north or south for uniform
illumination
Removal of obstructions
Windows: a tall window gives greater penetration
of light & a broad window gives greater diffusion
of light
Interior of the room: ceiling-white; upper portion
of wall-light tinted; lower portion of wall-dark so
as to give comfortable contrast to eyes
7. Day light measurement
Day light factor: It is the ratio of illumination at a given point
to illumination at a point exposed simultaneously to the
whole hemisphere of the sky excluding direct sunlight
10. Filament lamps
Widely used
Electric current heats up the tungsten filament
Accumulation of dust on the bulbs reduces illumination by
30-40%, hence needs cleaning frequently
11. Fluorescent lamps
Economical in use
Cool efficient
Simulates natural light
Glass tube filled with mercury vapour and an
electrode at each end
Inside tube is coated with fluorescent
chemicals, which absorb practically all the UV
radiation & remit radiation in all visible range
12. Lighting standards
Visual task : Illumination(lux)
Casual reading : 100
General office work : 400
Fine assembly : 900
Very severe tasks : 1300-2000
Watch making : 2000-3000
13. Biologic effects
Day light could cause the in vitro degradation of
bilirubin (used as therapeutic procedure)
Biologic rhythms of body temperature
Physical activity
Stimulation of melanin synthesis
Activation of precursors of vitamin D
Adrenocortical secretion
Food consumption
15. Sources of radiation
Natural (average person is exposed to 0.1 rad/yr)
◦ Cosmic rays
◦ Environmental
◦ Terrestrial radiation
◦ Atmospheric radiation
◦ Internal radiation
Man-made
◦ X-rays
◦ Radioactive fallout
◦ Miscellaneous
16. Cosmic rays
Originate in outer space
At ordinary living altitude their impact is about
35 mrad a year
At altitude above 20 km it is very high
A jet pilot receives about 300 mrad/year
17. Environmental
Terrestrial: Radio active elements & isotopes
present in man’s environment. Eg. Soil, rock etc.,
Atmospheric: the external radiation from the
radioactive gases. It is about 2 mrad/yr
Internal: from radioactive matter stored in the
body tissues, about 25 to as high as 80 mrad/yr
18. Man-made sources
X-rays: patients group/radiologists & technicians
(exposure to single x-ray film varies roughly from
0.02 rad to 3 rad)
Radioactive fallout: evenly distributed over
whole human race (33 mrems/person)
Miscellaneous: every day appliances (TV sets,
luminous wrist watches is too small to be
important)
19. Types of radiation
Ionizing radiation (able to penetrate tissues)
◦ Electromagnetic radiation (x-ray & gamma ray)
◦ Corpuscular radiation (electrons & protons)
Non-ionizing radiation (wavelengths longer than
those of ionizing radiation & includes UV radiation,
visible light, infrared radiation, microwave radiation
& frequency radiation)
20. Radiation units
Roentgen: it is unit of exposure the amount of
radiation absorbed in air at a given point i.e.,
no.of ions produced in 1ml
Rad: it is the unit of absorbed dose, the
amount of radioactive energy absorbed per
gram of tissue or any material
Rem: it is the product of the absorbed dose
and the modifying factors
21. Biological effects of radiation
Somatic
◦ Immediate
◦ Radiation sickness
◦ Acute radiation syndrome
◦ Delayed
◦ Leukemia
◦ Carcinogenisis
◦ Fetal developmental abnormalities
◦ Shortening of life
Genetic
◦ Chromosome mutations
◦ Point mutations
22. Radiation protection
The amount of radiation received from outer space
is estimated to be 0.1 rad a year
Additional permissible dose should not exceed 5
rad a year
Effective protective measures include proper use of
lead shields & lead aprons
Workers must wear a film badge or dosimeter,
beside periodic examinations, regular working
hours, recreation & holidays
