Term
| How does light influence how we perceive an object or person? |
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Definition
The way light illuminates an object helps define how think or feel about that object.
By changing the color, angle, intensity and focus of the light we can make the audience feel a certain way about what is going on. |
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Term
| What are the properties of a particle? |
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Definition
Photons and Electrons
Measurable: Mass, Charge, Spin and Decay |
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Term
| Why can light be considered a particle? |
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Definition
Due to the Photoelectric Effect (E = hf):
Increasing the intensity of light and it increases the number of electrons emitted from the surface but doesn’t increase the energy of each electron. |
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Term
| What are the properties of a wave? |
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Definition
A wave is a transfer of energy from one point to another without the transfer of a material between the two points. The main properties of waves are defined below. •Amplitude: the height of the wave, measured in meters.
•Wavelength: the distance between adjacent crests, measured in meters.
•Period: the time it takes for one complete wave to pass a given point, measured in seconds.
•Frequency: the number of complete waves that pass a point in one second, measured in inverse seconds, or Hertz (Hz).
•Speed: the horizontal speed of a point on a wave as it propagates, measured in meters / second. |
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Term
| What does diffraction mean? |
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Definition
The bending of waves around obstacles, or the spreading of waves by passing them through an aperture, or opening. |
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Term
| What does reflection mean? |
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Definition
| The phenomenon of a propagating wave (light or sound) being thrown back from a surface. |
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Term
| What does refraction mean? |
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Definition
| The bending of light rays or waves as they go from one material to another due to the differences in velocities in the material. |
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Term
| Why can light be considered a wave? |
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Definition
| Light is made up of packets, or chunks, of light in which Einstein called them photons. The photons have energy and vibrate. Light travels as particles and waves and both have been proven. The double slit experiment showed that light traveled as a wave but the “photoelectric effect,” as well as the “Davisson-Germer” experiment showed light as a particle. |
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Term
| What is wave-particle duality? |
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Definition
| Principle of quantum mechanics implying that light (and, indeed, all other subatomic particles) sometimes acts like a wave, and sometime acts like a particle, depending on the experiment being performed. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation tends to act more like a particle than a wave. |
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Term
| What is the visible spectrum? |
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Definition
| The Visible Spectrum is that part of the Electromagnetic Spectrum which can be seen with the naked eye. It consists of the frequencies between 380 nanometers and 780 nanometers (400-700nm). It consists of the colors Violet, indigo, blue, green, yellow, orange and red. |
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Term
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Definition
There are two basic types of light:
-Incandescence -Luminescence
Vibration of an atom Vibration of electrons
Thermal or blackbody emission Lower temperature
Heating it up until there is light Change of energy level releases photon
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Term
| What is the smallest particle of light, as we know it today? |
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Definition
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Term
| What does a reflector do? |
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Definition
| It re-directs light from the source to give it a specific shape and focus. |
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Term
| What is the Law of Specular Reflection? |
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Definition
| The angle of incidence equals the angle of reflection. |
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Term
| What is the point of incidence? |
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Definition
| The point of incidence is the point where the ray of incidence strikes the mirror. |
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Term
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Definition
| The normal line is a line drawn perpendicular to the surface at the point of incidence. |
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Term
| What is the angle of incidence? |
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Definition
| The angle between the incident (incoming) light ray and the normal line. |
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Term
| What is the angle of reflection? |
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Definition
| The angle between the reflected (outgoing) light ray and the normal line. |
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Term
| What are three types of reflectors? |
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Definition
•Ellipsoidal Reflector – A concave ellipsoidal surface used to focus rays from a light source at the near focal point onto the opposite focal point of the ellipse.
•Parabolic Reflector – A reflective surface generated by rotating a parabolic section around its axis. A light source placed at the focal point of the reflector will create a reflected beam of concentrated collimated light parallel to the axis of the reflector.
•Spherical Reflector – A reflector shaped like a portion of a sphere so that light from a point source at the center point of the sphere will be reflected back through the center point of the sphere. |
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Term
| What does a specular reflector do? |
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Definition
| A reflecting surface (polished metal or silvered glass) that gives a direct image of the source, with the angle of reflection equal to the angle of incidence (The Law of Specular Reflection). Also known as regular reflector. |
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Term
| What does a diffuse reflector do? |
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Definition
-A diffuse reflector will spread light in all directions.
-There are certain types of diffuse reflectors that offer more control.
•They are known as Spread Reflectors. A spread reflector will scatter the light but all reflected rays will be travelling along the same plane.
•Diffuse Reflectors will scatter light in such a way that each individual light ray in the beam strikes a point that will be different from the neighboring point. |
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Term
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Definition
| They will bend light through the process of refraction. |
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Term
| What does a spread reflector do? |
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Definition
| A spread reflector will scatter the light but all reflected rays will be traveling along the same plane. |
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Term
| What is a near zero reflector? |
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Definition
| Has almost no reflection. |
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Term
| What is a near perfect reflector? |
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Definition
| The surface of a perfect mirror reflects the incident ray without any attenuation. However, there is no such thing as a surface that will yield a perfect specular reflection due to the fact that it is impossible to polish a surface to a level where there are no facets at an atomic level. Even on the flattest of flat surfaces, there will be facets to some extent. |
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Term
| What does an ellipsoidal reflector do to the light? |
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Definition
| By mathematical definition an Ellipsoid has two focal points. When a reflector is placed at the focal point at that end, all rays of the light that strike the reflector will be diverted through the second focal point. The result is that an enormous percentage of the light from the source is directed in a manner that makes it easily usable. Ellipsoidal reflectors can improve the efficiency of an instrument by 75%. |
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Term
| What does a spherical reflector do to the light? |
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Definition
| If a light source is placed in the center of a spherical reflector, all of the rays will be reflected back 180 degrees of their original trajectory. This gives almost double the light output than would occur without the reflector. A spherical reflector will increase the efficiency of a lighting instrument by 40%. |
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Term
| What does a parabolic reflector do to the light? |
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Definition
| If a light source is placed in the focal point of a parabolic reflector, the rays of light will be reflected parallel to one another. This will give a great concentration of light in a tight beam, rather than an effused spread. Moving the source toward the reflector will spread the light, while moving the source away from the reflector will cause the light rays to converge. |
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Term
| What does an asymmetrical reflector do to the light? |
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Definition
| This reflector is not symmetrical around its axis as the previous reflectors have all been. In addition, the lamp is offset instead of being placed in the center of the reflector. |
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Term
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Definition
| A wave is a moving vibration through some material. That material is called the medium. Well-known examples are the surface waves of water (water is the medium) and sound (air is the medium). |
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Term
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Definition
| Optical density controls the index of refraction. If the light is moving from a medium with a low optical density (smaller index of refraction) to one of high optical density (bigger index of refraction) the light will bend towards the normal line. |
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Term
| What is the speed of light in a vacuum? |
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Definition
| 186,200 miles per second. |
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Term
| What is the Index of Refraction? |
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Definition
| The ratio between the speed of light in a vacuum and the speed of light in a medium is known as the index of refraction (speed of light in a vacuum divided by speed of light in the medium) and tells us how much the light will bend when it crosses the boundary between mediums. |
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Term
| How does light bend when crossing from a medium of a low optical density to a medium of a high optical density? |
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Definition
| The light will bend towards the normal line. |
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Term
| How does light bend when crossing from a medium of high optical density to a medium of low optical density? |
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Definition
| The light will bend away from the normal line. |
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Term
| When light is passing through a medium with non-parallel surfaces, how does the light bend? |
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Definition
| When the two surfaces are not parallel the bending is compounded due to the changing angle of the incident light at the normal line and the emergent ray will not be parallel to the incident ray. |
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Term
| What is the focus point of a lens? |
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Definition
| Where the parallel rays of the light converge. |
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Term
| What is the optical center of a lens? |
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Definition
| The optical center is an imaginary plane, based on the radii of the curvature of the surfaces of the lens, where light appears to bend in the lens. The Optical Center (vertical) may be the physical center of the lens if the curvatures of the opposite sides are the same or it may be offset if the curvatures are different. |
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Term
| What is the optical axis? |
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Definition
| The optical axis is a line drawn (horizontal) through the physical center of the lens. |
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Term
| What is the focal length of a lens? |
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Definition
| The focal length is measured along the optical axis from the optical center of the lens to the focal point. |
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