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Summary of Lighting Technology (7S880)
Clear and concise summary of the course 7S880.
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Summary Lighting Technology (7S880)Lecture 1 Light and radiation
History:
- Newton: light is little particles traveling in straight line
- Huygens: light is composed of waves, wave theory. Waves slow down when entering a
denser medium
- Maxwell: self-propagating electromagnetic waves travel with the speed of light, light is a
form of electromagnetic radiation
- Planck: quantum theory, black bodies emit light only as discrete packages of energy (quanta)
- Albert Einstein: wave-particle duality of light
- Packages of light are called photons
Order radiation: X rays, UV, Light, IR, microwave, radiowave
Light is: packages of energy and waves, wave particle dualismQph (energy photon)=h
(plancks constant)*v (frequency), (c0=lambda(wavelength)*v), c0 speed of light in vacuum.
The speed of light (c) in another medium calculated with refractive index n
Phenomenon is due to different refractive indices for different media, that’s why there are
differences in speed of light in different media
We can often ignore the wave nature of light, we assume light to propagate in straight lines within a
homogeneous medium since:
- The dimensions of media are larger than the wavelength of radiation
- Time relevant time intervals are longer than the duration of one oscillaton
UV is not light, but radiation. Light is ‘visually perceived radiant power’, a small
proportion of the electromagnetic spectrum, from 380-780 nm, lower wavelength is
more blue light. Colors from low to high wavelength: purple, blue, green, yellow,
orange, red.
Spectral power distribution of a light source:
Blue light has a smaller wavelength, so contains more energy according to formula
Light quantities:
- Radiometric quantity X , e indicated it is an radiometric quantity (see spectral
power distribution above), without it is a photometric quantity
- Sensitivity of receptor , Y received/ X emitted
- Spectral sensitivity , relative spectral sensitivity
- Effect Y related to given spectral sensitivity
- Often used sensitivity function, V(lambda)
curve, developed for photopic vision (during daytime), CIE standard
photopic observer, 2 degrees test field diameter. We are highly sensitive
to green part, 555 nm
,- V’(lambda), more shifted towards blue part, for scotopic vision (nightly),
CIE standard scotopic observer, 20 degrees diameter measured, peak 507
- Photopic above 3.4 cd/m2, scotopic below 0.034 cd/m2, in between it is
mesopicmix of two spectral response curve
- From radiometric to photometric quantities: we use the V(lambda curve),
photometric quantity X multiplication
factor Km * integral of radiometric quantity per wavelength * eye sensitivity to get a
photometric quantity. Multiplication factor Km: how much lumen we can usefully use out of
total watts being emitted or maximum luminous efficacy of radiation for photopic vision,
remember Km=683 lm/W. For scotopic K’m = 1699 lm/W.
- For every radiometric quantity we have a photometric quantity
o Luminous flux (Φ) in lumen (lm): relates to power, to describe
all light generated by lamps luminous flux = Km* (radiant flux
per wavelength (spectral power density) * V(lambda) * smallest
wavelength difference between 2 measures. The spectral power density is given as a
mean value for a small wavelength bands e.g. dlambda 5 or 10 nm
Calculation luminous flux = 683 (10*10*0,06) (correct answer 244513 lm),
we have a dlambda of 10 since we have measurements in 10 nm
o Luminous efficacy of radiation (K): calculation for radiant flux.
Ratio between luminous flux and radiant flux of light is luminous
efficacy of radiation.
o Illuminance (E) in lx: how much luminous flux is perceived by a given area:
when index 2 the surface is receiving light, when index 1 it is emitting light.
Horizontal illuminance: horizontal surface
Vertical illuminance: vertical surface
Mean illuminance: average of series of illuminance measures
Cylindrical illuminance/semi-cylindrical (e.g. front size of face), e.g.
Ez=1/4*(500+300+1000+100)
Typical lux values: outside sunny 100000 lx, overcast, 10000, workplace 500,
street lighting, 10, moonlight 0.05-0.2
o Luminous intensity (I) in cd: luminous flux emitted into a solid angle, used to
characterize the light distribution of a source . Planar angle of full circle is 2pi in
2D, in 3D 4pi, can be calculated with , when a small part of this is taken
with makes
o Luminance (L) in cd/m2: luminous intensity in a given direction related to the
emitting area, used to determine glare
or or
Affects brightness perception, used to evaluate glare
Luminance is not equal to brightness, brightness is a psychophysical quantity
not a photometric one, luminance can be measured. The functional relation
between luminance and brightness is non-linear
Luminance depends on the reflection of the surface, illuminance not
, o Luminous exitance (M) in lm/m2: refers to luminous flux emitted per
surface area
o Luminous energy (Q) in lm*h: used to describe total amount of
light a lamp can produce over its lifetime, area under curve luminous flux/time
o Luminous exposure (H) in lx*h: area under illuminance/time curve, used for daylight
exposure
o Luminous efficacy (n) in lm/W: measure of how much luminous flux is
generated in relation to power drawn, used in energy efficiency of lamp
o Other factors, luminance coefficient , luminance factor
- Material characteristics
o Luminous reflectance, transmittance, absorbance
o The total is 1
o Same as spectral reflection, transmission, absorption which is a function of: light
incidence and observation angle
Light propagation:
- Fundamental law of photometry: filling in
and gives
- Inverse square law: if the distance is increased by 2, the illuminance is 2 squared decreased.
Filling in in the fundamental law gives:
Minimum distance where this law can be applied is the minimum inverse square distance rp.
Different factors are effecting this: dimensions of light source or light emitting area,
luminance distribution, dimensions of sensor, maximum measurement uncertainty
- Lambert’s cosine law: a Lambertian radiator emits at a constant radiance or luminance in all
directionss, a perfect black body is a perfect Lambertian radian. Consequence this law: when
an area element on the surface is viewed from any angle, it has the same apparent
brightness.
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