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LIGHTING DESIGN LECTURE 2 â€“ Feb 1 st Lighting Terminology. Before we go on: an Introduction to basic lighting terms We quantify light as â€œlumensâ€ â€œpiecesâ€ of light Lumens of light striking a surface = Illuminance Expressed in Foot-candles
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Before we go on: an Introduction to basic lighting terms
We quantify light as “lumens”
“pieces” of light
Lumens of light striking a surface = Illuminance
Expressed in Foot-candles
Lumens of light leaving a surface generically = Exitance
Exitance is simply light leaving, with no indication of direction
Lumens of light leaving a surface in a specific direction in a specific density
Luminance is light leaving in a specific density as viewed from a specific vantage point
Luminance is most closely related to the assessment of “brightness”
These terms are all expressions of Lumens of light interacting in different ways
It is helpful to get used to the proper preposition for each interaction
We talk about Illuminance “onto” a surface
We talk about the exitance “of” or “from” a surface
We talk about the Luminance “of” or “from” a surface
Good lighting design is simply a study of where light ends up.
4 relationships shape our understanding of where light is most effective.
1. Adaptation: Humans have the ability to adapt to function under vastly different light levels
High-noon Sunlight is tens of thousands of times brighter than full-moonlight, yet we can read under both.
Excess light is wasted light as our visual system works to even out our experience.
2. Brightness: The subjective judgment of lighted objects in an environment.
Brightness is the product of contrast. Object are judged in relation to their surrounding.
“Bright” objects need only be brighter than their neighbors.
3. Phototropism: Humans notice bright things and ignore dark things
A few lighted objects can define the general feeling of a space (if they are in plain sight)
4. Vertical Vision: Humans tend to notice what is right in front of the.
Vertical surfaces (walls and objects) do more to define the impression of a space than the floor.
All of this means that a few well placed pieces of light can define a space as “bright”
Lighting design becomes a study of contrast and placement rather than a the application of even light levels throughout a space.
Lighting can be applied in two distinct steps
1. Lighting Specific surfaces: tasks, accents, local visual effects
Imagine that we can “paint” light on to specific objects as if with a brush or spray can.
These few specific pieces of light will draw attention and create a perceived brightness.
Every piece of applied light will inter-reflect and contribute to the overall ambience.
Assess these effects, then…
2. Augment the feeling of brightness
Apply light on to the vertical surfaces (and reflective surfaces) to increase the perceived brightness.
Lighting specifics, then assessing, then augmenting brightness / ambience accomplishes the following:
Minimizes the risk of wasting light.
Creates hierarchy and visual interest,
Leaves room for impacting lighting effects.
Reduces glare and eye strain
How does a typical space respond to this theory?
What is typical? Why?
What if we think in these two steps?
Light is a member of a large family of phenomena called electromagnetic radiation (EMR)
EMR is raw energy
Heat, light, x-rays, microwaves, U.V. are all examples of EMR (radiation)
EMR has no mass, no taste, no color
All EMR radiation travels at the same speed: “the speed of light”
EMR varies only in wavelength
Wavelength is measured in Nano-meters
We can symbolize EMR as tiny squiggly lines vibrating through space
We can diagram other types of EMR and what they do… remember: the only difference from one form of radiation to the next is… WAVELENGTH
Our eyes can detect only a small portion of the spectrum: so we call this portion the “visible spectrum”
Because we detect this EMR we name it. We call it light !
The visible spectrum includes radiation from about 380 Nano-meters (violet) to 770 nano-meters (red) in wavelength
SO… where does radiation come from, and why do we detect only a small portion of it?
The SUN has historically been our primary source of radiation
The sun emits almost every wavelength of EMR.
We would call this a very complete spectrum
Almost all of the sun’s radiation is blocked by our atmosphere
What types leak through and make it to the earths surface?
The visible spectrum, some IR and some UV
So we have adapted to detect and make use of these types of radiation
This is also why we have no defense mechanisms against the other type of EMR
We have learned to distinguish different combinations of radiation by translating the detection experience into “colors”
We have also become more sensitive to colors (wavelengths) of light which are more abundant
Plants are sensitive to red… why?
People are sensitive to green (545 nm)… why?
Light is electro-magnetic radiation in specific wavelengths detected by our eyes
For each specific wavelength or combination of wavelengths we have named our eye / brain response as a “color”
The mechanisms we use
Accommodation (focus at different distances)
Adaptation (adjust for dark or bright situations)
Diagram the human eye
Cornea: clear transmitting / refracting / protecting device
Iris / pupil: some of our dark/light adaptation (dilate)
Flexible to change shape to refract differently to accommodate (focus)
Presbyopia: the hardening of the lens as eye ages
Test your near point (flexibility)
Aqueous humor , vitreous humor
The retina: home to all of our photoreceptors (light detectors)
Described as three parts: periphery, macula, fovea
Can be permanently damaged
Populate the macula and fovea
Active in high light levels (called Photopic vision)
Responsible for color vision (if you perceive color, you are using cones)
There are three classes of cones, each class sensitive to different wavelengths
Three different classes / sensitivities of cones make color translation possible.
The classes are named for the photo pigment that they contain
RHO “R” cones: sensitive to “red” light (580 nm). Contain erythrolab
GAMMA “G” cones: sensitive to “green” light (540 nm). Contain chlorolab
BETA “B” cones: sensitive to “blue” light (450 nm). Contain cyanolab
Populate the periphery of the eye
Active in low light situations (called Scotopic vision)
Very sensitive to change and motion
Only come in one class (therefore Scotopic rod vision is monochromatic)
All rods are most sensitive to 545 nm. Contain the photo pigment Rhodopsin
Visualize how the eye measures light quantities.
The brain “sees”, the eyes merely “detect”.
Completeness of spectrum / CRI
The more wavelengths that come out of a light source, the more opportunity a surfaces has to reflect light
We measure the complexity / completeness of a light source. We call this the COLOR RENDERING INDEX or CRI
It is a numeric value ranging from 0-100 (the higher the better)
Historically the CRI is assigned by experimenting on people
some sample to get used to
Incandescent light: 100
Fluorescent: 75 - 95
Metal halide: 75-90
High pressure sodium: 25
Low pressure sodium: 25
Balance of spectrum / Color temperature
If a light source gives of more of one wavelength than another, than our brains translation of the light is a slight color experience
We have devised a numeric description of the color produced by the imbalance called CORELATED COLOR TEMPERATURE
Expressed as a temperature in degrees Kelvin K or “Kelvins”
Extracted from the behavior of black metals as they are heated up: red to orange to yellow to blue etc.
This behavior follows a predictable path where green would appear we get a very pale “neutral”
We use it most to help describe fluorescent sources.
The Architecture of Light, Chapters 3 thru 7 & 9