light

1. Light

2. • What is light?
• A form of energy whose interaction with retina gives
a sensation of sight.
• A visible portion of electromagnetic radiation
spectrum.

3. • Electromagnetic Spectrum
• The range of frequencies (the spectrum) of
electromagnetic radiation and their respective
wavelengths.
• Visible spectrum and invisible spectrum

6. • Visible Spectrum
• LIGHT lies in visible spectrum.
• Between 400nm to 700nm.
• White light consists of seven colours: VIBGYOR
• Violet, Indigo, Blue, Green, Yellow, Orange, Red

7. • Invisible Spectrum
1. Cosmic rays
2. Gamma rays
3. X rays
4. Ultraviolet rays
5. Infrared rays
6. Micro waves
7. Radio waves

8. • Optical Radiation
• Optical radiation lies between X-rays and microwaves
in the electromagnetic spectrum and is subdivided
into seven wavebands
• These seven domains are
• Ultraviolet C (UV-C), 200–280 nm;
• Ultraviolet B (UV-B), 280–315 nm;
• Ultraviolet A (UV-A), 315–400 nm;

9. • visible radiation, 400– 780 nm;
• Infrared A (IRA), 780–1400 nm;
• Infrared B (IRB), 1400–3000 nm; and
• Infrared C (IRC), 3000– 10000 nm.
• As with all electromagnetic radiation, the shorter the
wavelength, the greater the energy of the individual
quanta, or photons, of optical radiation

10. Wavelength Absorption
• Wavelength absorbed by cornea and sclera
• UV-C, UV-B ,
• IR-B, IR-C,
• Wavelength absorbed by crystalline lens
• UV- A
• Wavelengths in the range 400– 1400 nm (visible light
and near infrared), pass through the ocular media to
fall on the retina

11. Thermal Effect
• The visible wavelengths stimulate the retinal
photoreceptors giving the sensation of light while the
near infrared may give rise to thermal effects.
• The refractive surfaces of the eye focus the incident
infrared radiation on the retina, it can cause retinal
damage, e.g. eclipse burns.

12. Nature of Light
• Dual nature of light.
1. Wave nature
2. Particle nature.

13. • WAVE THEORY OF LIGHT
• A portion of electromagnetic spectrum
• Light behave as s wave as it passes through air,
vacuum or other transparent medium also
transparent Ocular tissue.
• Path of light is straight if no obstacle encountered.
• Light really travels as waves although its path is often
represented as a 'ray’.

14. • Huygens in 1678 proposed that light moves in the
form of waves from light source.
• These waves consists of crests and troughs
• CREST
• The highest surface part of a wave is called the crest.
• TROUGH
• The lowest part is the trough

16. • Wavelengths
• The wavelength, λ, is defined as the distance
between two symmetrical parts of the wave motion.
• Cycle
• One complete oscillation is called a cycle.
• Amplitude (A)
• The maximum displacement of an imaginary particle
on the wave from the base line

18. • Phase
• Any portion of a cycle is called a phase.
• Phase Difference
• If two waves of equal wavelength (but not
necessarily of equal amplitude) are travelling in the
same direction but are 'out of step' with each other,
the fraction of a cycle or wavelength by which one
leads the other is known as the phase difference

20. • Incoherent waves
• Light waves that are out of phase are called
incoherent.
• Coherent waves
• light composed of waves exactly in phase is termed
coherent.

21. WAVEFRONTS
• Wave fronts are surfaces connecting points
with the same phase of a wave.

22. • Shape of wavefronts depends upon nature of source
• Spherical wavefronts - Point Source
• Cylindrical wavefronts – Slit Source
• Wave motion transmit energy, not matter.

23. Phenomenon explained by wave nature ?

24. Particle Nature of Light
• Light exhibits some characteristics of particle
(photons) when it is absorbed or generated by light
source.
• Einstein in 1905 proposed that light of a given
frequency consists of quanta with same energy.
• Quanta or photons – units in which electromagnetic
radiations are measured.

25. Phenomenon's
• Photoelectric effect
• Scattering
• Emission
• Absorption

26. Color vision
• The colour of any object is determined by the
wavelengths emitted or reflected from the surface.
• White light is a mixture of wavelengths of the visible
spectrum.
• Colour is perceived by three populations of cone
photoreceptors in the retina which are sensitive to
light of short (blue), middle (green), or long (red)
wavelength

27. • A congenital colour vision defect occurs if a cone
pigment is absent. OR
• If there is a shift in its spectral sensitivity.
• Deuteranopia, Protanopia and Tritanopia indicate
absence of green, red and blue cone function
• Deuteranomaly, Protanomaly and Tritanomaly
indicate a shift in the corresponding cone sensitivity

28. • X-chromosome
• carries genes encoding for red and green pigment
• Chromosome 7
• carries the blue pigment gene.
• Of men 8% and of women 0.5% have a defect of the
red/green system.
• The commonest is deuteranomaly which occurs in
5% of men and 0.3% of women.
• Tritan defects are rare

29. • Congenital colour defects characteristically affect
particular parts of the colour spectrum.
• Acquired colour defects occur throughout the
spectrum but may be more pronounced in some
regions.
• For example, acquired optic nerve disease tends to
cause red–green defects.

30. • Clinical Testing of Colour Vision
• Farnsworth–Munsell (FM) hue 100 test
• D-15 test
• Ishihara pseudoisochromatic test plates
• Lanthony New Colour Test