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Summary slides of lecture 1 t/m7
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This is a summary of the slides from lecture 1 t/m 7 (lecture 8 till 10 excluded)
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Lecture 1Light and radiation
Different theories
Wave theory of light (Christiaan Huygens): light is emitted as a series of waves in
a medium called the “luminiferous ether”. Waves slowed down by entering a
denser medium
Corpuscular theory of light (Sir Isaac Newton): light is composed of
“corpuscles”(very small particles) which travel in straithg line with a finite velocity
and contain kinetic energy
Electromagnetic theory of light (James Clerk Maxwell): electromagnetic waves would
travel through space at a constant speed equal to speed of light. Light is form of
electromagnetic radiation
Quantum theory of light (Max Planck): explains difference wave theory and
electromagnetic quanta = black bodies emit light only as discrete packages of energy
Particle theory revisited (Albert Einstein): quantum of light was named a photon. The wave
particle duality of light was formed.
Summarized
Wave theory of light Waves (straight lines)
Corpuscular theory of light Particles
Electromagnetic theory of light Light form of electromagnetic radiation
speed of light
Quantum theory of light Packages of energy (explains difference
wave and electromagnetic)
Particle theory revisited Photon, wave particle duality of light
Wave particle dualism
Due to different refractive indices for different media the image of a different media bends
Unless otherwise noted: in building lighting it is assumed that light propagates in straight
lines within a homogeneous medium this can be assumed since the dimensions of the
media are much larger than the wavelength of radiation and the relevant time intervals are
longer than the duration of one oscillation.
Light
Light: visually perceived radiant power and is a small portion of the electromagnetic
spectrum
visible radiation (light) = 380nm – 780 nm
Blue light contains more energy cause lower wavelength eph = h x (c0/wavelenght)
Light quantities and definitions
Radiometric (energetic) quantity is indicated by the index “e”
Eye sensitivity funciton V(labda): photopic vision and peak at 550 nm and applicable for
luminances above 3.4 cd/m2
Eye sensitivity funciton V’(labda): scotopic vision and peak at 500nm, valid for luminance
below 0.034 cd/m2
,Mesopic vision: between 3.4 and 0.034 cd/m2
Radiometric and photometric quantities
Quantity Definition Use
Luminous flux ([lm] Photometric quantity that Describes light generated by
relates to power lamps
Luminous efficacy of Ration between luminous
radiation flux and radiant flux
Illuminance (E[lx]) How much luminous flux is To define design
received by giving area illuminances for specific
surfaces
Luminous intensity (I[cd]) Luminous flux emitted into a Characterize the light
solid angle distribution of a luminaire
Luminance (L[cd/m2]) Luminous intensity in a Impacts brightness
given direction related to perception under normal
emitting area circumstances. Used to
evaluate glare rating
Luminous existance Luminous flux emitted per Difference with illuminacne
(M[lm/m2]) surface area is that luminous existance
refers to the emitted
luminous flux
Luminous energy (Q[lm x h]) Time integral of luminous Describes total amount of
flux light that a lamp can
produce over its lifetime by
weighing its luminous flux
with lamp life
Luminous exposure (H[lx x Time integral of illuminance Daily light exposures
h] E (morning vs evening), e.g.
health effects
Luminous efficacy (n[lm/W]) How much luminous flux is Indicator for the energy
generated by an electrical efficiency of a lamp
light source in relation to
electrical power drawn
Outside you receive illuminance 100 000 lx and at workplace 500lx
luminance range from sun is 160000 and candle is 0.75, lamp is 200-2600 cd/m2
The intensity of a light source is dependent on luminous flux and luminous intensity same
luminous flux, but smaller angler means higher intensity
, Luminance is not brightness, but it impacts it (non linear relation)
brightness: psychophysical quantity and not a photometric one, based on perception
Material characteristics
Material characteristics: used such that the model represents the actual situation. Can
also be defined as function of light incidence or a function of observation angle.
Summary of main photometric quantities
1. Luminous flux
2. luminous intensity
3. illuminance
4. luminance
Basic principles of light propagation
Inverse square law
distance x2 luminance existance (lm/m2) is divided by 4
This law can only be applied when the distance r is large in comparison to the source. The
minimum distance where the law can be applied is called minimum inverse square
distance rp.
Lambert’s cosine law
The radiance of certain idealized optical sources is directly proportional to the cosine of the
angle – with respect to the direciton of the maximum radiance – from which the source is
viewed.
lambertian radiator emits at a constant radiance or luminance (perfect black body)
Consequence lambert’s cosine law. When an area element on the surface is viewed from
any angle, it has the same apparent brightness
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