Thursday, 18 February 2010

Notes from lecture on 3 illumination engineering

Eye and visions
Instructional objectives
1. Identify Similarity between eye and camera system
State nervous system use for adaption of eye.
List factors for good lighting
Define glare

Incandescent, phosphorescence, Fluorescence,
Colour temperature is categorized by colour temperature

Iris, focusing lens, retina
resembles a camera in structure and action

Iris is like the shutter
Lens of eye is like the lens of a camera which focuses lens
Retina is like film

Optical image is formed on retina. Nerves enable us to see.
Crystalline Lens
Optic nerve.

Iris is a diaphram that regulates light entering eye by expanding and contradicting pupil.
Crystaline lens is more flexible than camera lens. It can be convex flat,
is is controlled by cilliary muscles
Screen is retina.
Fovea most acute sport of vision where fine detailed is formed
Rest of retina takes care of orientation.

Communicates through optic nerves
Double nerves
Rods - Dim Light Night vision
Cones - Concentrated in central region known as fovea

Cones decreases from fovea
they do form colour, sensitivity,
Photopic cone cells
discriminate fines details
critical observation
dense pack
Cone cell vision does not work below 0.01 ft lamberts

Foot Lambert is is amount of light falling on surface area defined as sum involving 1 candle.
So cone cells are not sensitive below certain levels of foot Lamberts.
Two sets of nerves cones and rods
Scotopic vision (rods)
Takes over when light vision less than 0.01 ft lamberts
No or little colour discrimination
Quite grey in appearance
sees as silhouettes

Shift from rod to cone is purkinjee effect.
Unlike camera which is rigid.

Upon increase in intensity of illumination
decrease in pupil size and greater detail with cone cells.

pupil diameter 1.2 - 2 mm.

Eye functions under varying illumination by changing pupil size and verve system.

Pupil size
Large Dim light rod
Small bright cone

do not get detail with rods

Eye unconsciously takes care of this.
Human eye is chromatic dispersive power

near vision easily focus blue
strenuous red
Far vision easily focus red
strenuous on blue

Pupil opening
Large Flattest shape distance object can focus on red
Small convex shape near objects easy to focus on blue as it has short test wave length,.
At about 1m from eye no difference in accommodation.
can focus on all colors equally.
cones better at longer wavelengths than rods.

rods best at 507 nm blue green
cones 550

seeing is primary purpose of lighting
must see artificial light is as close to natural light.
prevent defective vision.

Artificial lighting extend out activity period.
Visibility of object will depend on size of object,
details of object, level of illumination.
Contrast or color in brightness has an impact.
The ways eyes function need observation time.
size of object illumination requirement,
deficiency must be compensated

visibility will depend on nature of eye defects.
Fatigue physical or optical.
Depends in nature of defects.
Every man made system has fatigue.

Eye fatigue
Retinal, muscular,

Glare, due to brightness some might not see board due to glare due to bright light,
Glare means intense illumination in plane.
when you have to move focus, you cause muscular adjustments.
Glare causing strain and fatigue on muscles on eye.

After a full days work pupil is dilated.
We are now involved in many eye tasks.
Need a break to offset fatigue.
weekend offsets fatigue of working week.
Pupilliary changes must not become permanent if so will nedd glasses
Eye defects known due to age, use and abuse.
Reading fine prints in dim light can abuse eye.
Strained muscles will occur due to difference in size images.
refractory errors.
So lower retinal sensibility needs more illumination.
Countless impression formed on retina.

photopic - cones
scotopic - rods
fine image details need good cone vision.
lens becomes convex when you want to observe fine detail.

Human eye is achromatic in nature.
cone cells better 550nm yellowish green hue
good lighting should aim to prevent defects in vision.

visibility depends on efficacy of individual

Visible range of light 380nm to 700nm
arc lamp emits selective radiations in visible zone
isle of man mansions