1. Fundamentals of lights
LIGHT & SOUND
INTD 302
ASSOC PROF DR NOOR HANITA ABDUL MAJID

2. What is light?
The Illuminating Engineering Society of North America (IESNA) defines light as
“radiant energy that is capable of exciting the retina and producing a visual sensation.”

3. Electromagnetic spectrum

4. The electromagnetic spectrum extends from low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometers down to a fraction of the size of an atom.

5. Light as part of the electromagnetic spectrum

6. Light as a Wave
Wave Terminology
Wavelength - distance between two like points on the wave
Amplitude - the height of the wave compared to undisturbed state
Period - the amount of time required for one wavelength to pass
Frequency - the number of waves passing in a given amount of time

7. Properties of light

8. Properties of light Basic Concepts in Optics
1. When light encounters a surface, it can be either reflected away from the surface or
refracted through the surface to the material beneath.
2. Once in the material, the light can be transmitted, absorbed, or diffused (or some combination) by the material.

9. Properties of light
When light waves, which travel in straight lines, encounter any substance, they are either reflected, absorbed and transmitted.

10. Types of surfaces

11. transmission
When light passes through an object, it is called transmission. Absorption, reflection, refraction, and diffusion all affect light transmission.

12. absorption
Instead of completely transmitting light, an object can absorb part or all of the incident light, usually by converting it into heat.
Many materials absorb some wavelengths while transmitting others, which is called selective absorption.

13. reflected, refracted, dispersed or diffracted

14. reflection three types of reflection: specular, spread, and diffuse
1. A specular reflection, such as what you see in a mirror or a polished
surface, occurs when light is reflected away from the surface at the same angle as the
incoming light’s angle.
2. A spread reflection occurs when an uneven surface reflects
light at more than one angle, but the reflected angles are all more or less the same as
the incident angle.
3. A diffuse reflection, sometimes called Lambertian scattering or
diffusion, occurs when a rough or matte surface reflects the light at many different angles.

16. Specular reflections demonstrate the law of reflection
the angle between the incident ray and a line that is normal (perpendicular) to the surface is
equal to the angle between the reflected ray and the normal.
The angle between an incident ray and the normal is called the incident angle, denoted by the symbol θ. The angle between a reflected ray and the normal is called the reflected angle, denoted by the symbol θ´.

17. Reflection
The first property of light we consider is reflection from a surface, such as that of a mirror.
One of the properties of light is that it reflects off surfaces. Among other things, this reflection allows us to see images in mirrors. We see the images in mirrors as apparently coming from behind the mirror because our eyes interpret it in this manner. But when we see ourselves reflected in the mirror and raise our left arm, the image apparently raises its right arm.

18. Refraction (Snell’s law)
When light travels from one material to another (such as from air to glass), it refracts — bends and changes velocity.
Refraction depends on two factors: the incident angle (θ) and the refractive index of the material, denoted by the letter n.

19. Refraction
Refraction is the bending of light as it passes between materials of different density.
Another property is the speed of light, which is the fastest anything has been observed to move. In a vacuum, the speed is 300 million meters per second. At that speed, it takes light one ten thousandth of a second to travel around the earth. When light enters a material, it slows down. The amount depends on the material it enters and it’s density. For example, light travels about 30% slower in water than it does in a vacuum, while in diamonds, which is about the most dense material, it travels at about half the speed it does in a vacuum. This slowing down of light plays a role in another property, refraction.
Refraction means that light bends when it passes from one medium to another. When light enters a denser medium from one that is less dense, it bends toward a line normal to the boundary between the two media. The greater the density difference between the two media, the more the light bends. This property is used with respect to optical devices such as microscopes, corrective lenses for vision, magnifying lenses, and so on.

20. Dispersion
The velocity of light in a material, and hence its index of refraction, depends on the wavelength of the light. In general, n varies inversely with wavelength: it is greater for shorter wavelengths. This causes light inside materials to be refracted by different amounts according to the wavelength (or colour). This gives rise to the colours seen through a prism.
Variations of index of refraction in glass
Color
Wavelength
Index of Refraction
blue
434 nm
1.528
yellow
550 nm
1.517
red
700 nm
1.510

21. Dispersion of white light
Rainbows are caused by a combination of dispersion inside the raindrop and total internal reflection of light from the back of raindrops.

22. Diffraction
Diffraction is the apparent "bending" of light waves around obstacles in its path.
Diffraction through a slit

23. Huygen's principle
This bending is due to the points along a wave front that act as if they were point sources. Thus, when a wave comes against a barrier with a small opening, all but one of the effective point sources are blocked, and the light coming through the opening behaves as a single point source, so that the light emerges in all directions, instead of just passing straight through the slit.

24. Diffusion (Scattering)
When light strikes a perfectly smooth surface, the reflection is specular, as explained in "Reflection.”
When light strikes a rough surface, the light is reflected or transmitted in many different directions at once, which is called diffusion or scattering.
The amount of diffuse transmission or reflection that occurs when light moves through one material to strike another material depends on two factors:
· the difference in refractive index between the two materials
· the size and shape of the particles in the diffusing material compared to the wavelength of the light
For example, the molecules in air happen to be the right size to scatter light with
shorter wavelengths, giving us blue sky.

25. Vision and light

26. What Exactly Is a Lumen?
Light measurements can either be radiometric or photometric.
Radiometric measurements measure all the wavelengths of a light source, both visible and invisible.
Photometric measurements measure only the visible wavelengths of light.
The total electromagnetic energy that a light source emits across all wavelengths is known as radiant flux, and is measured in watts. The total energy that a light source emits across the visible wavelengths of light is known as luminous flux, and is measured in lumens.

27. Since visibility only has meaning in relation to a human viewer, photometric data takes into consideration the varying sensitivities of the human eye to different wavelengths (colors) of visible light.
the human eye is most sensitive to light in the green part of the spectrum, around a wavelength of 550 nanometers (nm), and is progressively less sensitive to light toward both the red and blue ends of the spectrum.

28. The Measurement of Lamp Output
One of the most important considerations in selecting a light source is how much light it will generate. The unit of measure used for determining light is the lumen. One lumen equals the amount of light generated by a single standard candle.
While lumens are a measurement of light output from the light source (lamp), it only indirectly correlates to how much usable light there is for a certain application. This is true because visual light is actually how much illuminance is reflected from the surface(s) it hits. Light can be absorbed or reflected in different ratios depending on the surface it touches. This accounts for many other factors involved in lighting an area such as the type of fixture (reflector) used, how dirty or clean the fixture is, the total size of the space (room) to be illuminated, the color (reflectivity) of the walls, floor, and ceiling, among other factors.
To determine how much light actually illuminates a surface, a different measurement, foot-candle (fc.), must be used. A foot-candle is 1 lumen of uniform illuminance over the area of 1 square foot. The metric equivalent to foot-candles is lux (1 lumen per square meter). To convert fc. to lux, multiply the fc. by To convert lux to fc. multiply lux by

30. Lux
While lumens measure the total output of a light, lux measures the amount of light that strikes a point on a wall. 1 lux is equal to 1 lumen per square meter. This can be measured with a light meter. The problem is that the value will go down as the light is moved further from the wall. Also the value will vary depending on whether the reading is taken in the hotspot or spill of the flashlight beam. Still, it is an easy measurement to make and many flashlight reviewers will use it. It can also be used pretty accurately to get a profile of how the brightness of a light varies with time. Reviewers can take an initial reading, call that 100%, and then chart how the light intensity varies until the battery is drained. See Wikipedia article for more information on lux lux is said to be roughly equal to the light of a full moon.

31. Luminance/ Brightness
In casual usage, the apparent power of a light source is often mistakenly referred to as a fixture’s “brightness.” Brightness is subjective, and varies depending on such factors as the distance of the light source from the viewer, the viewing angle, and the conditions of the light source’s surroundings. Lumen measurements, in contrast, are based on carefully defined standards and test conditions, rather than on subjective impressions.

32. Brightness is a description of light output, which is measured in lumens (not watts). Light bulb manufacturers include this information and the equivalent wattage right on the packaging. Common terms are "soft white 60," "warm light 60," and "60 watt replacement."
Incandescent Bulbs
(watts)
Minimum Light Output
(lumens)
Common ENERGY STAR Qualified Bulbs (Watts) 25
250
4 to 9 40
450
9 to 13 60
800
13 to 15 75
1,110
18 to 25
100
1,600
23 to 30
125
2,000
22 to 40
150
2,600
40 to 45

33. Brightness
Another measurement of light is luminance, sometimes called brightness. This measures light leaving a surface in a particular direction, and considers the illuminance on the surface and the reflectance of the surface.

34. Illuminance versus luminance
The human eye does not see illuminance; it sees luminance. Therefore, the amount of light delivered into the space and the reflectance of the surfaces in the space affects your ability to see.

35. Quantity Measures
Luminous flux is commonly called light output and is measured in lumens (lm).
Illuminance is called light level and is measured in footcandles (fc).
Luminance is referred to as brightness and is measured in footlamberts (fL) or candelas/m2 (cd/m2).

36. ILLUMINATION Quantity of Illumination
Exhibit 1 shows the interaction between light output, light level, and brightness. Although they are quantitative measures, they directly affect the quality of illumination.
Light output-lumens
Light level-illumunance (footcandles)
Brightness –luminance (footlamberts)

37. Determining Target Light Levels
The Illuminating Engineering Society of North America(IESNA) has developed a procedure for determining the appropriate average light level for a particular space. This procedure used extensively by designers and engineers recommends a target light level by considering the following.
the task(s) being performed (contrast, size, etc.)
the ages of the occupants
the importance of speed and accuracy

38. Appropriate type and quantity of lamps and light fixtures may be selected based on:
fixture efficiency
lamp lumen output
the reflectance of surrounding surfaces
the effects of light losses from lamp lumen
room size and shape
availability of natural light (daylight)

39. Note: energy savings
When designing a new or upgraded lighting system, one must be careful to avoid overlighting the space. In the past, spaces were designed for as much as 200 footcandles in places where 50 footcandles may not only be adequate, but superior. This was partly due to the misconception that the more light in a space, the higher the quality. Not only does overlighting waste energy, but it can also reduce lighting quality.

40. Level of illuminance three factors dictate the proper level:
age of the occupant(s),
speed and accuracy requirements,
background contrast.
For example, to light a space that uses computers, theoverhead light fixtures should provide up to 30 fc of ambient lighting. The task lights should provide the additional footcandles needed to achieve a total
illuminance of up to 50 fc for reading and writing.
(illuminance recommendations for specific visual tasks, refer to the IESNA Lighting Handbook, 1993)

41. Three quality issues of lighting
+ glare + uniformity of illuminance + color rendition
Light Bulbs*
Type
Common Application
Efficiency
Colour Rendering**
Incandescent
homes
poor
good
Fluorescent
offices
fair to good
Mercury
factories, offices
fair
fair to moderate
Low pressure sodium
roadway
High pressure sodium
factories, commercial
Metal Halide

42. Quality Measures
Visual comfort probability (VCP) indicates the percent of people who are comfortable with the glare (brightness) from a fixture.
Spacing criteria (SC) refers to the maximum recommended distance between fixtures to ensure uniformity.
Color rendering index (CRI) indicates the color appearance of an object under a source as compared to a reference source

43. Quality of Illumination
Improvements in lighting quality can yield high dividends. Gains in worker productivity may result by providing corrected light levels, improved color rendering, and reduced glare.
In retail spaces, attractive and comfortable lighting designs can attract clientele and enhance sales.

44. What are some of the most common lighting problems?
Poor lighting can cause several problems such as:
* insufficient light - not enough (too little) light for the need,
* glare - too much light for the need,
* improper contrast,
* poorly distributed light, and
* flicker.

45. What should you know about insufficient light?
Poor lighting can be a safety hazard - misjudgement of the position, shape or speed of an object can lead to accidents and injury.
Poor lighting can affect the quality of work, specifically in situation where precision is required, and overall productivity.
Poor lighting can be a health hazard - too much or too little light strains eyes and may cause eye discomfort (burning, etc.) and headaches.

46. The amount of light we need varies and depends on:
* the type of task being done (such as demands for speed and accuracy), * type of surfaces (does it reflect or absorb light), * the general work area, and * the individual's vision.

47. Principles of Glare

48. Glare
Perhaps the most important factor with respect to lighting quality is glare. Glare is a sensation caused by luminances in the visual field that are too bright.
Discomfort, annoyance, or reduced productivity can result.
A bright object alone does not necessarily cause glare, but a bright object in front of a dark background, however, usually will cause glare. Contrast is the relationship between the luminance of an object and its background.
Although the visual task generally becomes easier with increased contrast, too much contrast causes glare and makes the visual task much more difficult.

49. You can reduce glare or luminance ratios by not exceeding suggested light levels and by using lighting equipment designed to reduce glare. A louver is commonly used to block direct viewing of a light source. Indirect lighting, or uplighting, can create a low glare environment by uniformly lighting the ceiling.

50. TYPES OF GLARE
Disability glare results when a light source reflects from or otherwise covers the visual task, like a veil, obscuring the visual target, reducing its contrast and making the viewer less able to see and discriminate what is being viewed. The problem is illustrated with the drawing below

51. TYPES OF GLARE
Discomfort glare arises when light from the side of the task is much brighter than the light coming from the task. The eyes attempt to focus on the light from the task, but so much extra light is entering the eye from the side that the visual processes are confused and it is difficult to concentrate for long periods. The geometry is illustrated below.
In the example below, light from a window enters the reader's eyes and makes it difficult to see the lesser amount of light coming from the reading task. Prolonged exposure to such conditions can result in headaches and eye fatigue.

52. Illuminance on Tasks
The uniformity of illuminance is a quality issue that addresses how evenly lightspreads over a task area.
Although a room’s average illuminance may be appropriate, two factors may compromise uniformity:
improper fixture placement based on the luminaire’s spacing criteria (ratio of maximum recommended fixture spacing distance to mounting height above task height)
fixtures that are retrofit with reflectors or louvers that narrow the light distribution
Non-uniform illuminance causes several problems:
inadequate light levels in some areas
visual discomfort when tasks require frequent shifting of view from underlit to overlit areas
bright spots and patches of light on floors and walls that cause distraction and generate a low-quality appearance

53. Measurement of light

55. Light Output
The most common measure of light output (or luminous flux) is the lumen. Light sources are labeled with an output rating in lumens. For example, a T12 40-watt fluorescent lamp may have a rating of 3050 lumens.
Inventory of a bulb

56. lumen depreciation
Similarly, a light fixture’s output can be expressed in lumens. As lamps and fixtures age and become dirty, their lumen output decreases (i.e., lumen depreciation occurs). Most lamp ratings are based on "initial“ lumens (i.e., when the lamp has been operated for 100 hours).
Lumen maintenance curves represent the lamp manufacturer’s estimate of the best lamp lumen output plotted over time.

58. Light Level
Light intensity measured on a plane at a specific location is called illuminance. Illuminance is measured in footcandles, which are workplane lumens per square foot. You can measure illuminance using a light meter located on the work surface where tasks are performed.
Using simple arithmetic and manufacturers Photometric data, you can predict illuminance for a defined space.(Lux is the metric unit for illuminance, measured in lumens per square meter. To convert footcandles to lux, multiply footcandles by )

59. Lighting Levels
This chart below summarizes the light levels that occur under daylight and low-light conditions.  The equivalent metric measure of light level (lux) compared with the condition (fc)

60. Measuring Units Light Level - Illuminance
Illuminance is measured in foot candles (ftcd, fc, fcd) (or lux in the metric SI system). A foot candle is actually one lumen of light density per square foot, one lux is one lumen per square meter.
1 lux = 1 lumen / sq meter = phot = foot candle (ftcd, fcd)
1 phot = 1 lumen / sq centimeter = lumens / sq meter = lux
1 foot candle (ftcd, fcd) = 1 lumen / sq ft = lux

61. Common Light Levels Outdoor
Common light levels outdoor at day and night can be found in the table below:
Condition
Illumination
(ftcd)
(lux)
Sunlight
10,000
107,527
Full Daylight
1,000
10,752
Overcast Day
100
1,075
Very Dark Day 10
107
Twilight 1
10.8
Deep Twilight .1
1.08
Full Moon
.01
.108
Quarter Moon
.001
.0108
Starlight
.0001
.0011
Overcast Night
.00001

62. Common and Recommended Light Levels Indoor
The outdoor light level is approximately 10,000 lux on a clear day. In the building, in the area closest to windows, the light level may be reduced to approximately 1,000 lux. In the middle area its may be as low as lux. Additional lighting equipment is often necessary to compensate the low levels.
Earlier it was common with light levels in the range lux for normal activities. Today the light level is more common in the range lux - depending on activity. For precision and detailed works, the light level may even approach lux.

63. The table below is a guidance for recommended light level in different work spaces:
Activity
Illumination (lux, lumen/m2)
Public areas with dark surroundings
Simple orientation for short visits
Working areas where visual tasks are only occasionally performed
Warehouses, Homes, Theaters, Archives
150
Easy Office Work, Classes
250
Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories
500
Supermarkets, Mechanical Workshops, Office Landscapes
750
Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres
1,000
Detailed Drawing Work, Very Detailed Mechanical Works
Performance of visual tasks of low contrast  and very small size for prolonged periods of time
Performance of very prolonged and exacting visual tasks 
Performance of very special visual tasks of extremely low contrast and small size

64. wasalam