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LIGHTING DESIGN LECTURE 2 – Feb 1 st Lighting Terminology. 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

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lighting design lecture 2 feb 1 st lighting terminology

LIGHTING DESIGN LECTURE 2 – Feb 1stLighting Terminology

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

  • Basic light interactions are always about “Lumens” of light interacting indifferent ways.
lighting design lecture 2 less is more

LIGHTING DESIGN LECTURE 2Less is More

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.

  • A small quantity of light in the right place is much more effective than any quantity of light in the wrong place.
lighting design lecture 2 less is more4

LIGHTING DESIGN LECTURE 2Less is More

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

  • Light specifics first, then assess the effect. Then apply light to augment the ambient brightness.
lighting design lecture 2 less is more9

LIGHTING DESIGN LECTURE 2Less is More

How does a typical space respond to this theory?

lighting design lecture 2 less is more10

LIGHTING DESIGN LECTURE 2Less is More

What is typical? Why?

What if we think in these two steps?

  • .
lighting design lecture 2 the physics of light

LIGHTING DESIGN LECTURE 2The Physics of Light

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

  • .
lighting design lecture 2 the physics of light12

LIGHTING DESIGN LECTURE 2The Physics of Light

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

lighting design lecture 2 the physics of light14

LIGHTING DESIGN LECTURE 2The Physics of Light

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

lighting design lecture 2 the physics of light15

LIGHTING DESIGN LECTURE 2The Physics of Light

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?

The fundamentals:

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”

  • Color is not a property of an object… color is our brain’s translation of radiation being reflected from an object to our eyes
lighting design lecture 2 fundamentals of vision the eye

LIGHTING DESIGN LECTURE 2Fundamentals of Vision: The Eye

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)

Crystalline lens

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

lighting design lecture 2 fundamentals of vision the eye17

LIGHTING DESIGN LECTURE 2Fundamentals of Vision: The Eye

Cones

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

Rods

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

lighting design lecture 2 fundamentals of vision the eye18

LIGHTING DESIGN LECTURE 2Fundamentals of Vision: The Eye

Visualize how the eye measures light quantities.

The brain “sees”, the eyes merely “detect”.

  • For human vision performance and revealing the world around us we are usually concerned with “white” light
  • BUT… white is a subjective experience (like all “color”) and our definition is constantly changing…. So we break it down in to two issues:
  • COMPLETENESS OF SPECTRUM & BALANCE OF SPECTRUM
lighting design lecture 2 color science and light sources

LIGHTING DESIGN LECTURE 2Color Science and Light Sources

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

Daylight: 100

Incandescent light: 100

Fluorescent: 75 - 95

Metal halide: 75-90

High pressure sodium: 25

Low pressure sodium: 25

lighting design lecture 2 color science and light sources20

LIGHTING DESIGN LECTURE 2Color Science and Light Sources

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.

lighting design lecture 2 for next week

LIGHTING DESIGN LECTURE 2For Next Week

Reading Assignment:

The Architecture of Light, Chapters 3 thru 7 & 9