Chapter 2 Flashcards
Light This refers to:
- Electromagnetic radiation ;and
- Radiant Energy
within the portion of the electromagnetic spectrum that can be perceived by the human eye
Electromagnetic radiation
makes things visible is classified by the wavelength into a system known as the electromagnetic spectrum
Radiant Energy
Natural Light source
- Moon and Star;
- Sunlight
Source of Light
- Natural Light source;and
- Artificial Light Source
It is when the sun sets, day turns into night and it becomes dark.
Moon and Star
The most popular and mostly used light source of photographers. It is free and no need to be transported. But it is not always there where we want it. It is uncontrollable but can be controlled using the camera controls
Sunlight
Classification According to it’s Intensity
- Bright sunlight/ Distinct Sunlight
- Hazy Sunlight
- Dull Sunlight/Cloudy
- Overcast Sky/ Cloud Bright
- Heavy overcast/ Cloud Dull
This is the direct sunlight striking the subject. It is the brightest of all, it is highly directional, images taken with distinct sun is characterized by extreme highlights and deep shadows and it provides the highest contrast in a picture
Bright sunlight/Distinct sun
It is a hazy sunlight when the sun is covered by thin clouds but still clearly visible and it is illuminating your subject, it produces soft shadows and moderate highlight and contrast is also moderate, while rays are directional.
Hazy Sunlight
Objects in open space cast no shadow. It is cloudy when the sun is shining bright but covered with thick moving clouds, other parts of the sky maybe clear, lighting is even throughout and not directional, it does not cast practical shadows on your subject and contrast is relatively fair.
Dull Sunlight/ Cloudy
Sun is bright but not visible, light is soft and not directional, skies may be covered with stationary clouds and it provides no shadows and low contrast
Overcast Sky / Cloudy Bright
This is practically the same as overcast sky but generally darker and light is dull. It provides very poor contrast and static cloud is so thick where one cannot tell the overhead position of the sun.
Heavy Overcast/Cloudy Dull
Light sources of this category are man-made and are divided into the
continuous radiation and the short duration. Continuous radiation, those that can give illumination continuously, short Duration and it gives a brief flash of light produced by a burning metallic wire (flash bulb) or an electrical discharge through a gas – filled tube (electronic flash). There are different classifications
Artificial Light Source
this refers to some units are portable battery operated and are easily carried and can meet the rugged and rigorous demand for field work
UV Lamp
This refers to Light Amplification through Simulated Emission of
Radiation. By illuminating certain items with LASER, they would fluoresce or could be made to stand out in sharp contrast from their background. This was especially significant in locating dried biological items
LASER
This refers to far more expensive alternative to forensic LASER. It uses a variety of band pass filters to provide a high intensity beam of non – coherent light.
Alternative Light Source (ALS)
This refers to a wide variety of relatively inexpensive light sources which use filtered white light.
.Forensic Light Sources (FLS)
Continues Radiation
- Carbon Arc
- Incandescent
- Photoflood lamps
- Fluorescent Lamps
This refers to a pair of carbon rods connected in series with a resistance across direct current.
Carbon Arc
This refers to a conducting filament enclosed by a glass bulb heated by the electric current until emits lights.
Incandescent
This refers to lamps that can be placed up very high producing deep shadows underneath protruding surfaces, if subject is a person standing, he will appear gloomy and sombre. These can be placed to shine from below giving mysterious and strange effects of frights to observers of the picture.
Photoflood lamps
This refers to illumination in an electric discharge lamp of the mercury – vapor type. The coating fluoresces and sends out light of low brilliance with visible zone.
Fluorescent Lamps
Short Duration Radiation
- Chemical Flash Lamp
- Electronic Flash Lamp
This refers to light that produces by the rapid burning of metal wire, foil or primer powders. To produce a rapid and complete burning, the bulb is charged with O2, the lamp flashed once.
Chemical Flash Lamp
This is consisting of a slender glass tube filled with a gas (Xenon), a high voltage electrical discharge is passed through coiled tube, causing the gas to glow.
Electronic Flash Lamp
Light Angles
- Front Lighting
- Side Lighting
- Back Lighting
- Overhead Lighting
Distinct sun is used as front lighting when it comes from behind the photographer. It is a common belief that photographs taken at early in the morning or late in the afternoon is better compared to photos taken in any other time of day. The light, when the sun is low, is oftentimes described as magical. Colors are warm, shadows are long, and subject glow with razor sharp clarity.
Front Lighting
This type of lighting happens mostly in the morning and afternoon when the sunlight hits the subject from either the right or left flank of the photographer. It brings out textures, patterns, and shapes of objects.
Side Lighting
This type of lighting happens when the sun strikes the subject from behind or when the sun is directly in front of the photographer. Light coming straight from the back of the subject in portrait produces a bright edged outlined around it. Backlighting also brings out shapes and good profile as well as silhouettes of your subjects
Back Lighting
This normally occurs at noontime where sun is directly above your subject. This angle of lighting is generally not recommended for taking portraits. Strong dark shadows are cast at the subjects’ eyes. However, it can be corrected with a fill – in flash.
Overhead Lighting
Theories of Light
- Wavelength of Light
- Quantum Theory
When incident light hits a medium, three things might happen, the light maybe:
• Reflected
• Absorbed
• Transmitted
It occurs whenever an object changes the direction of a light wave but does not allow the wave to pass through it. Reflected light maybe Specular or Diffused. When light strikes the surface and rebound it is said to be reflected, and it is called incident light. The angle which it strikes is called incident angle
REFLECTION
It is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another. Bending of light when passing from one medium to another.
REFRACTION
It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. It is also described as the bending of light when it hits a sharp edge of an opaque
DIFFRACTION
Examples of Diffraction
a. CD or DVD
b. Hologram
c. Interference
d. Rectilinear
e. Absorption
f. Filtration
g. Polarization
h. Fluorescence
i. Transmission
act as a diffraction grating to form the familiar rainbow pattern we see when looking at a disk;
CD or DVD
A picture that changes when looked at from different angles) on a credit card
Hologram
This refers to the color that can be produced by interference of light waves in thin film like soap bubbles or a film of oil floating in water.
Interference
This refers to the nature of light that normally travels in straight line.
Rectilinear
This refers to the nature of light to be absorbed in the process of dark surfaces.
Absorption
This refers to the character of light to be altered from its colorless into visible state.
Filtration
This refers to the process by which the vibration of light are confined to definite plane, the speed of light can be measured
Polarization
This happens when molecules of the fluorescent material absorb energy at one wavelength and radiate it at another wavelength.
Fluorescence
This refers to the light that passes through an object.
Transmission
Medium of Lights
- Transparent objects
- Translucent objects
- Opaque Objects
It allows sufficient visible light to pass through them that the object on the other side may be clearly seen. It transmits 90% or more of the incident light.
Transparent objects
It allows light to pass, however diffuse it sufficiently that objects on the other side may not be clearly distinguished . In some cases the objects on the other side may be recognizable but sharp detail and outlines are obscured. It transmits 50% or less of the incident light
Translucent objects
It is so greatly diffuse the light that recognizing the object on the other side is very difficult if not impossible.
It divert or absorb light.
Opaque Objects
Simplistically, we can think of light travelling as a wave. A typical wave form (e.g., ripples on the surface of water) has crests (or peaks) and troughs (or valleys).
Wavelength
The light that we see is only a part of a tremendous range of energy called the ?
Electromagnetic Spectrum
Kinds of light in electromagnetic spectrum
a. Visible Lights
b. Invisible Lights
Visible Lights
Red
Orange
Yellow
Green
Blue
Indigo
Violet
It range from 685-605 mμ
RED
It range from 605- 585 mμ
ORANGE
It range from 585-560 mμ
YELLOW
It range from 560-475 mμ
GREEN
It range from 475-455 mμ
BLUE
It range from 455-440 mμ
INDIGO
It range from 440-405 mμ
VIOLET
The light that cannot be detected by the naked eye is the invisible spectrum. The left region of the visible light is called the ultra violet region. The right region of the visible light is called infrared region which are too long in wavelength to excite the retina of the eye. It is detected by the skin as heat.
Invisible Lights
Invisible Radiation with wavelength shorter than 400 mμ
- Ultraviolet lights
- X-ray
- Gamma rays
- Cosmic rays
It is used to photograph fingerprints on multi – colored background, documents that are altered chemically or over writings and detection of secret writings.
Ultraviolet lights
electromagnetic energy having a wavelength that ranges between 10 – 30 millimicrons.Objects which are opaque as seen by the naked eye can be penetrated by x –rays.To produce a shadow photograph of an internal structure of solid objects, x –rays is suitable.
X-ray
Used in recording or photographing objects hidden by opaque mediums
Gamma rays
high energy charged particles, originating in outer space, that travel at nearly the speed of light and strike the Earth from all directions.
It also include high energy electrons, positrons, and other subatomic particles.
usually refers to galactic cosmic rays, which originate in sources outside the solar system, distributed throughout our Milky Way galaxy.
Cosmic rays
Invisible Radiation with wavelength longer than 400 mμ
- Infrared Light
- Radio Waves
- Microwaves
- Hertzian Waves
lights having wave length greater than 700 millimicrons. It wavelength ranges from 700 – 800 millimicrons.
It is not a color or any kind of red. It is an invisible rays and it is only
detected by the human skin as heat.
It is used in taking photographs of obliterated writing, burnt or dirty documents. Also known as “Blackout photography”.
Infrared light
These light waves have the longest wavelength of all lights.
It is used for communicating through the modification and amplification of sound waves.
Radio Waves
excite the water molecules in food, heat them up, and pass the heat throughout the food. It can harm the body because it can heat the water molecules in deep tissues.
Microwaves
An electromagnetic wave produced by the oscillation of electricity in a conductor (as a radio antenna) and of a length ranging from a few millimeters to many kilometers.
Hertzian Waves
The presence of all color
WHITE
The absence of all colors or the absence of light
BLACK
Primary colors of light rays
- Red
- Green
- Blue
Secondary/ Contemporary colors of light rays
- Yellow
- Cyan
- Magenta
Light rays
- Primary colors of light rays
- Secondary/Contemporary colors of light rays
- Color mixing of lights
- Color addition
- Color Subtraction
Coloring Matters
- Primary colors of coloring Matters
- Secondary colors of coloring Matters
- Tertiary colors of coloring Matters
- Color mixing of coloring Matters
- Neutral Colors
Primary colors of coloring Matters
- Red
- Yellow
- Blue
Secondary colors of coloring Matters
- Orange
- Green
- Violet
Tertiary colors of coloring Matters
- Yellow - orange
- Yellow - Green
- Blue - Green
- Blue - Violet
- Red - Violet
- Red - Orange
Neutral Colors
- Gray
- Black
Qualities of Light
- Intensity
- Color
- Direction
- Contrast
- Quality
The amount of light reflected by the performer and the background. Also referred to as quantity of light and it refers to how bright or dim the light source is.
INTENSITY
also known as the temperature of the light reflected by the performer and the background
COLOR
The light determines the length and location of the shadows cast by the performer and the three dimensional props around him.
DIRECTION
refers to the difference in brightness
between the brightest and darkest parts of the image which is the contrast between highlight and shadow areas. Highlights are the brightest parts of the image and shadows are the darker regions of an image
CONTRAST
It is not something we can measure. It is, instead, something we describe based upon visual perception.
QUALITY
the most pertinent, particularly in the design of lenses. It is best illustrated by the dropping of stone in a pond of still water. The series of wave which travels outward from the center point are just like wave that travels in all direction from a source with equal velocity. This theory maybe used to illustrate reflection, interference, refraction, diffraction and polarization.
Wavelength Theory
Max Plank theorized in 1900 that light might be made up of little bundles of energy named quanta
Quantum Theory
He measured the speed of light in 1976
OLE ROMER
Forensic Light Source
- Latent Fingerprint Detection
- Bodily Fluids
- Hair and Fibers
- Questioned Documents
The primary application of a forensic light source is for enhancing the detection of latent fingerprints. The use of fluorescent enhancement processes that compliment a light source greatly increases the types of surfaces from which a latent fingerprint can be detected.
Latent Fingerprint Detection
It will actually glow under the light source illumination.
Bodily Fluids
It will also glow under UV or visible light and will stand out strongly for collection
Hair and Fibers
A tunable forensic light source can be used to identify slight variations in ink type by viewing ink responses as the color of the light is tuned through the visible and infrared regions.
Questioned Documents
