This document discusses luminous transmittance, haze, clarity, and photoelasticity. It defines luminous transmittance as the ratio of transmitted to incident light, and haze as light deviated more than 2.5 degrees from the incident beam. Clarity refers to minimal light scattering of less than 2.5 degrees. Photoelasticity is the property of some plastics to become doubly refractive under stress when viewed through polarized light, allowing analysis of stress and load paths. Test methods and factors that affect these properties are also outlined.

1. Luminous transmittance & Haze
Clarity
Photo elasticity
Amal Raj R B
1st M.sc BPS
Cbpst, kochi

2. LUMINOUS TRANSMITTANCE & HAZE
 Luminous transmittance is defined as the ratio of transmitted light to the incident
light.
 It is expressed as % of light transmitted.
 Luminous transmittance measures the amount of light passes through a sample.
Luminous transmittance = transmitted light
incident light
 Haze is defined as the cloudy appearance comes on the surface of specimen.
 The amount of transmitted light is deviated more than 2.5°c from the incident
beam .
 Haze is caused by surface imperfections ,density change .

3. Significance
 Light that is scattered, up on passing through a film or sheet of material can
produce a hazy or smoky field when objects are viewed though the material.
 Haze and luminous transmittance values are especially useful for quality
control and specification purpose and are primarily used in products or uses
where in true colour and visibilities are prerequisites.
 Window glazing requires low haze and high light transmittance where as
housing material for the light fixture requires high transmittance and haze.

4. Test method
 ASTM D 1003-07 : Standard test method for Haze and Luminous transmittance
of transparent plastics.
Specimen and conditioning
 Commonly disc of 50mm diameter is used.
 Test specimen is conditioned at 23 ± 2ºc and 50 ± 5% relative humidity for not
less than 40 hours prior to test.

5. Equipment

6. Procedure
 Test sample is placed between the specimen holder and the lens.
 Light from the light source is allowed to fall over the sample.
 Test is conducted by taking four different consecutive readings and
measuring the photocell out put as follows:-
T1 = specimen and light trap out of position
T2 = specimen and reflectance standard in position
T3 = light trap in position specimen and reflectance
T4 = specimen and light trap in position
Result
 Total transmittance Tt=T2/ T1
 Diffuse transmitted Td=[T4-T3(T2 /T1) ] / T1
 Haze percent=Td/Tt ×100

7. Factors affecting
 Defects in specimen
 Effect of incorporation of additives
 Type of material

8. CLARITY
 Clarity refers to the property of transmitting light which as minimal scattering when
passing through the object.
 If the transmitted light deviates less than 2.5°C from the incident angle, the
material is said to be clear.
Significance
 Clarity, which may also be prescribed as quality of image formation
through a sheet ends upon the linearity of the passage of light ways
through material.
 Haze measurement depend upon wide angle scattering while clarity
is determined by small angle scattering.

9. Test specimen and conditioning
 Specimen may be any sheet or film.
 Specimen is conditioned at 23 ± 2ºc and 50 ± 5% relative humidity.
Procedure
 The optical alignment of photometric unit is checked.
 The image of source aperture is centred precisely.
 Centring is controlled by micro adjust receiving aperture assembly, which is standardised
until a reading of 100 is obtained.
 The beam is completely blocked with apiece of black folt or paper and the knob is adjusted
to zero.
 The sample is placed and the receptor position is re adjusted.
 If slit optics are used , the specimen may be rotated its own axis to a maximum value of
transmitted light.
 The reading at different positions or orientations may be taken and results are taken.

10. Factors affecting
 Humidity
 Wavelength of light
 Particle size.

11. PHOTO ELASTICITY
 It is the property exhibited by some transparent solids whereby
the become doubly refractive, under stress.
 Most of the plastics exhibit stress-Optical properties when
subjected to internal or external stress and viewed through
polarised light.
Significance
 This properties of the transparent materials are useful in stress analysis.
 Used to determine residual stress and degree of orientation in molded parts.
 It is a non-contact optical method for determining stress and load paths in
structures or components.

12. Specimen and conditioning
 The test specimen can be a sheet or moulded part.
 Specimen is conditioned at 23 ± 2ºc and 50 ± 5% relative humidity.
Equipment
 The instrument designed to observe objects under
polarised light are called polariscopes.
 Two types of polariscopes are there:-
The transmission polariscope and
The reflection polariscope.

14. Procedure
 The specimen is placed in the center of the polarizing medium viewed from the opposite side of the light
source.
 The number fringes or rings formed due to the polarized light can be related to the extent of stress.
 Higher order of fringes represents high stress level and whereas unstressed areas is represented by low-order
of fringes.
 The close spacing of fringe represents high stress gradient and uniform colour indicates uniform stress in the
material.
 Several additional techniques are used in conjunction with the basic photo elastic concept, Which is used to
analyse complex problems :-
 Strobo elasticity
 Thermo photo elasticity
 Photo-visco elasticity
 Scattered light photo elasticity

15. Factors affecting
Residual stress:-
The presence of residual stress, which in turn depends on mould design,
gate size and location, weld line etc. changes the photo elasticity of the
material.