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Compiled by ILDA's Terminology Standardization Committee,
Patrick Murphy, Pangolin Laser Software, chair.

1. Introduction
2. Lasers and Optical Devices
3. Laser Projection Equipment
4. Projector Subsystems
5. Laser Shows and Special Effects
6. Computer Graphics for Laser Shows
7. Scientific and Technical Terms
8. Safety
9. Index

Lasers and Optical Devices

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Index

The first requirement of a laser show is, of course, a laser. This section defines various types of lasers, as well as the optical devices used with them. Air-cooled laser A laser using fans to force air over the laser tube and the power supply. Air- cooled lasers have the benefit of needing no water supply, although the fan noise can sometimes be a disadvantage. Usually only small and medium power lasers are air-cooled. Very small lasers, typically helium-neon, need no fans. Although technically they are "air cooled" via convection, the term is usually applied only to fan-forced cooling. Argon laser A laser filled with argon gas. It gives off green and blue light. The strongest lines are at 514 nm (green) and 488 nm (blue). Argons range from small 15 milliwatt 110 volt air-cooled models to large 50 watt 440 volt water-cooled systems. Argon lasers are the most common type of light show lasers since they provide usable brightness at a reasonable cost. Chiller A refrigration unit sometimes used with water-cooled lasers. It includes a compressor and thus can perform more cooling than a heat exchanger. See also:Recirculator. Dichroic filter, Dichroic mirror A piece of glass with an optical thin-film coating that transmits certain colors (wavelengths), and reflects the remaining colors. Dichroic filters are used to combine or eliminate specific colors as needed in a laser projector. Dichroic mirrors are used to maximize the amount of light reflected from a laser of a particular wavelength. Dichroics should be handled with care to prevent damage to the coating. See also:Color box. Diffraction grating A material, usually flexible plastic, containing microscopic lines (gratings) that break up light passing through it. They are used with lasers to create special beam or graphic effects. Shining a laser image through diffraction gratings produce multiple copies of the original image. The most common grating produces a grid image. Other types of diffraction gratings produce a linear, circular, or abstract patterns. Most gratings are used in the laser projector, but some pop music light shows distribute inexpensive cardboard glasses with grid diffraction gratings to the audience. Diode laser A semiconductor similar to an LED (light-emitting diode) but which produces coherent light. Diode lasers are small and efficient, which has led to their use in compact disc players and pen-type laser pointers. Currently, diode lasers are too dim or expensive for most light show uses. This is likely to change over the next few years. See also:Solid-state laser. Exciter See Power supply. Fiber optic cable Flexible glass or plastic strands made into a cable, used to carry light from one place to another. There are two main types. Transmission fibers carry the beam with as little loss as possible. They are used to transmit the laser's light to remotely located projection devices. Display fibers have no cable jacket, so some light scatters out the side of the strands. The strands themselves become a special effect, such as a laser-lit "whip" or a glowing "rope" wrapped around objects. Front-surface mirror A piece of glass with an exposed broadband reflective optical coating. In a conventional back-surface mirror, the reflective coating is protected with a heavy paint-like substance; reflections are seen through the glass. In a front- surface mirror, light does not have to travel through the glass to reach the coating. Mirrors used in laser work are almost always front-surface, as they can reflect up to 99.8% of the incident light and they have no secondary reflections. Front- surface mirrors require greater care in handling to prevent damage to the coating. See also:Mirror. Head 1) A laser tube enclosed in a case: the laser head (as opposed to the laser power supply). 2) A set of X-Y scanners which can produce laser graphics. A projector may have a number of heads. For example, a four-head projector can produce four different sets of graphics simultaneously. Heat exchanger A cooling unit sometimes used with water-cooled lasers. Hot water from the laser is cooled by water-to-water or water-to-air heat transfer. There is no active refrigeration, as in a chiller. See also:Recirculator. Helium-neon laser A laser filled with a helium/neon gas mixture. Most produce red-orange light having a wavelength of 633 nanometers. "HeNe"s are low powered, in the 0.5 to 50 milliwatt range. Most run on 110 volts, come with built-in power supplies, and need no special cooling. Some HeNes are made to produce orange (612 nm), yellow (594 nm) and green (543 nm) light. These have less power than a red HeNe of the same tube size and input power. Helium-neon lasers are the most common type of gas laser. Because of their relatively low power, in laser display they are used only for small-scale light shows and studio monitors. Krypton laser A laser filled primarily with krypton gas. It produces red light, with yellow, green and blue also available with specially tailored optics. It has a very strong red line at 647 nm. Kryptons are similar to argons (the same tube design can be used for both). However, kryptons give off less light power than an equivalent argon. Krypton lasers are primarily used when a powerful red light is needed. Laser A device which produces a coherent beam of light. The beam remains parallel for long distances and contains one or more extremely pure colors. Light show lasers are usually gas-filled tubes using high voltage current to cause the gas to glow. Mirrors at each end of the tube help amplify a process called "stimulated emission". Most of the stimulated emission light travels between the two mirrors; about 1% comes out of one of the mirrors to create the beam we see. The gas used determines the color (or colors) of the beam. Gas lasers remain the overwhelming choice for display applications. The four main types used are a helium-neon mixture, argon, krypton, and an argon-krypton "mixed gas" mixture. "Laser" was derived from "Light Amplification by Stimulated Emission of Radiation". See also:Head, Helium-neon laser, Argon laser, Krypton laser, Mixed gas laser, Power supply, Diode laser, Solid-state laser. Mirror Large mirrors are used to reflect the beam coming from a projector, forming a beam sculpture or matrix in the air. Usually the mirrors are surrounded by black metal, so light which might miss the mirror is harmlessly dissipated. Small mirrors mounted on actuators can be activated to reflect the beam out over the audience or onto large mirrors to form a beam sculpture or matrix. Small mirrors on precision mounts are used within projectors as steering mirrors to reflect the beam from place to place inside a projector. Tiny mirrors are used on the shafts of laser scanners, which move the beam at high speeds to form graphics. All of the mirrors above are usually front-surface mirrors. Mixed gas laser Many gas lasers contain mixtures of various gases, such as helium and neon. In the laser show industry, however, "mixed gas" usually refers to an argon-krypton mixture used to get a white-light beam containing red, green and blue lines. Yellow lines are additionally available for applications such as four-head projectors with one head each for red, yellow, green and blue. See also:White-light laser. Power supply A device converting readily available power, usually standard alternating current, into voltages necessary to energize laser tubes. It may also include other functions such as monitoring the laser's light output or current draw. A power supply is usually closely matched to a particular type of laser tube. Power supplies for high-power lasers (0.5 watt and above) often require 208 or 440 volts three-phase, and are cooled with flowing water. The supply is one of the two main parts of a laser; the other is the laser head. A power supply is also known as an exciter. Recirculator A pump used to recycle water, found in either a chiller or heat exchanger. The term "recirculator" is sometimes erroneously used to mean either of the more specific devices. Solid-state laser A laser where the lasing medium is a solid material such as a ruby rod. These can be optically pumped by a flashlamp or diodes. Currently, solid-state lasers are too expensive for most light show uses. This may change over the next few years. The most promising solid-state laser uses a material called Nd:YAG, producing up to 50 watts of green light at 532 nm. Water-cooled laser A laser using water to cool the laser tube. Often the laser power supply's electronics are also water-cooled. A gas laser (the type used in most laser display applications) is relatively inefficient. For example, an argon-filled laser producing 10 watts of light requires around 10,000 watts of electricity. In such a laser, water is used to carry off the 9,990 watts of excess energy as heat. Flow rates of two gallons (9 liters) per minute are typical. In many areas, the water can simply flow through the laser and down a drain. In water conservation areas, a chiller or heat exchanger is used to recycle the cooling water. Water supply considerations are always important to laser show producers. Even a brief interruption can cause problems. At best, flow sensors shut down the laser when the supply is inadequate. At worst, an expensive tube can overheat and be irreparably damaged. White-light beam Broadly, a laser beam which contains a number of different wavelengths (colors) so the beam appears white. If the beam is passed through a prism or diffraction grating, it is separated into individual laser beams, each of a single specific wavelength. More specifically, a white-light beam ideally contains an equal mixture of red, green and blue light. It can be from a single white-light laser or from two or three lasers whose beams have been combined into a single beam. White-light beams are primarily used in RGB laser projectors. See the definition of white-light laser for more information on what constitutes an "equal mixture" of light. White-light laser Many lasers can produce a number of wavelengths (colors) simultaneously. A white-light laser is designed to give a good balance of red, green and blue wavelengths. Usually the laser is intended for an RGB laser projector. (Some models also deliberately add yellow light for specialized 4-color projectors.) Most white-light lasers use an argon/krypton gas mixture. It is somewhat difficult to produce an equal balance of desired colors, and to keep this balance consistent during the lifetime of the laser tube. At present, there are no standards defining the exact wavelengths and color proportions for a laser to be called "white-light". In addition, the sought-after color balance can be defined either as equal amounts on a photometer, or as visually equal amounts. Since the eye is much more sensitive to green, a visually equal or "photopically balanced" laser has roughly five times more power in red and blue than in green. Most white-light lasers today are not photopically balanced. See also:Mixed gas laser.

Laser Projection Equipment

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A laser projector uses a laser's beam and produces projected graphics, beams, lumia or other visual effects. This section covers general terms used with laser projectors and their parts. The next section, "Projector Subsystems", discusses more specifically how the various sections of a projector relate to each other. AOM (acousto-optic modulator) A device used for dimming and blanking a laser beam. It can also be used for color control. In an AOM, a laser beam is shone through an acousto-optic crystal. By applying an electric signal to the crystal, the beam's intensity (brightness) can be modulated. For blanking and intensity control, a single AOM is used. For color control, three AOMs can be used on separate red, green and blue beams. Using additional optics, the beams are recombined to form a single beam whose color depends on the AOMs' settings. (For easier color control, more specialized PCAOMs are used. These require only one crystal to modulate a white-light beam, and they need no recombination optics.) The primary advantage of an AOM is its speed. It can be modulated fast enough to control the intensity or color of single points within a complex scanned image. However, it is more complex to interface with slower-reacting scanners, since timing adjustments must be made. See also:Blanking, Scanner blanking, PCAOM. Actuator A device that allows for the positioning of optical elements in a laser beam or for low-speed beam steering. Some examples: Mirrors on an actuator arm direct beams to different devices in a projector or out over an audience. Dichroic filters on actuators are used in color boxes. A beam block on an actuator is used to create a shutter. Actuators are typically a low-speed, heavy-duty version of an open loop scanner which allows for variable positions. Two-position solenoid-type devices can also be used. Barrel distortion A distortion caused by projecting onto a convex surface. For example, a grid projected on the outside of a dome has outwardly curved edges, where the centers curve out and the corners pull in. Single-axis barrel distortion occurs when projecting on the outside of a cylinder. The distortion can be alleviated using optical elements, electronic devices or software to counter-distort the image. The opposite of barrel distortion is called pincushioning. Beam block See Mask. Beam splitter A device which transmits part of a laser beam and reflects the other part. Usually, a beam splitter is a piece of glass with optical coatings; the type of coating determines the ratio between transmittance and reflectance. Using beam splitters, a laser's beam is divided and sent to two or more devices simultaneously. Blanking The technique of turning the laser beam on and off with precise control (as opposed to chopping). For scanned graphics, blanking allows images to have disconnected sections where the beam is hidden. Blanking can be digital (on/off) or analog (continuous intensity control). The same techniques used for blanking control can be used to control intensity of red, green and blue beams, for color mixing. See also:Acousto-optic modulator, Scanner blanking.

The following terms are suggested for the subsystems within a projector. These definitions are primarily for use within the context of the entire projector, to help distinguish one system from another. These terms have been carefully defined. This is because fine distinctions can become extremely important when specifying the equipment to be provided at a laser show, or when drawing up contracts for installations. Optics plate A metal plate drilled and tapped with holes, often in a grid configuration. The optics plate is usually the base on which the projector is built. Galvo, galvanometer Refers to the basic galvanometer itself, without an attached mirror mount or mirror. Scanner A galvo with an attached mirror. There are often three parts, the galvo, a mirror mount, and a mirror. See scanner for more information on general usage. Scanner amplifier Usually refers to the scan amp board only. Does not include a power supply or chassis unless this is specifically stated (in sales literature, etc.). Scanner head A pair of scanners in an X-Y mount with mirrors. Does not include the scanner amps, although those may be mounted close to the scanner head. Usually does not include any blanking system. Projector head Scanner head, plus any special optical effects such as beam switchers and lumia, in a finished chassis. Usually used when the laser beam is fed via fiber optic cable to a number of projector heads arranged on a stage or set. Does not include the scanner amps, although those may be mounted inside the projector head. Does not necessarily include a blanking device or system. Blanking system The blanking system cannot be assumed to be in either the scanner head nor in the projector head. The blanking system is usually set apart from the scanner head (scanners plus mount). It may also be separated from a fiber-fed projector head, since the beam is often blanked before being launched into the fiber. Therefore, the blanking system should be discussed as a separate subsystem; for example, when specifying number and location of heads. Laser projector Laser, scanner head, blanking system, special optical effects, and scanner amps, all in a single chassis. The inclusion of the laser, blanking and scanner-related electronics makes a laser projector more comprehensive than a projector head. Laser system A laser projector plus a signal source such as a tape playback unit, computer, or operator console. Beam table Optics plate plus special optical effects, usually beam positioning actuators, but also can include lumia and other effects. Does not include the laser. Beam projector Beam table plus laser. Usually implies no graphics scanning capability.

There are two main uses of display lasers: laser shows and special effects. In a show, the laser is the primary attraction. As a special effect, the laser supports a primary attraction. The following terms are widely used in describing shows and effects. Abstract Laser-projected images which are usually non-representational (as opposed to graphics). This implies using synthesizers or other techniques which do not afford point-by-point position control of the beam, and usually implies using scanners to create the abstract image. Usually excludes lumia, diffraction gratings, or similar non-scanner techniques. Beam effects Using the laser's beam as a sculptural element in space (as opposed to shining it on a screen to create graphics). The beam can be static or kinetic. If static, it is usually reflected off a series of widely spaced mirrors to create a "beam sculpture" or "beam matrix". If kinetic, it can be shot directly into space (over an audience), or can be directed to different groups of mirrors to create moving beam sculptures. A common technique is to scan the beam through theatrical smoke; if a line is scanned you see a plane of laser light, if a circle is scanned you see a cone. These effects require high power lasers and often require smoke, dim lighting and other environmental controls. See also:Cone, Fan. Beam sequence A beam effect where beams are directed to different mirrors in quick sequence. This gives a Star Wars-type impression of shooting beams bouncing around the performance arena. Color modulation, color mod Rapidly varying the color of the laser beam. In beam effects, color mod can be used on the entire beam matrix or can be sequenced in individual beams. In graphics effects, color appears to "chase" through an image. A classic light show effect is to project a dense spiral pattern, then use color mod to create shifting zones of colors pulsating through the image. See also:Chopping. Cone A beam effect where the beam is rapidly scanned to enclose space. For example, by scanning a circle, the effect looks like a cone of light emanating from the projector location. Other shapes can be scanned; for example, a square produces a pyramid "cone". Theatrical fog or smoke is often used to make the scanned light more visible. See also:Beam effects. Fan A beam effect where the beam is rapidly scanned from side-to-side, usually through theatrical smoke. If the scanning is smooth, the audience sees a plane of light. If the beam scans discrete positions, the audience sees a ribbed fan of light. The fan can be rotated and translated to produce a moving fan effect. Theatrical fog or smoke is often used to make the scanned light more visible. See also:Beam effects. Graphics Laser-projected designs, usually representational (as opposed to abstract) such as logos or drawings. Graphics implies point-by-point control of the beam position, which in turn implies computer control of laser scanners. A computer can generate non-representational designs, but these are normally classed as graphics rather than abstracts. Hologram A light-sensitive film which captures and plays back light wave interference patterns. One of the most striking results is the true three-dimensional nature of the recreated holographic image. Image holograms are not usually used in laser display technology. They are mentioned here because of a frequent misconception that laser shows can present "floating" 3D holographic projections. Although a holographic image can appear to be floating in front of the film plate, the viewer must always be looking at or through the hologram. Viewing angles are usually limited to one or two people at a time, and image size is usually one cubic meter or less. At present, there are no free-floating "Princess Leia" Star Wars-type holograms. Note: The term is hologram ("a laser recording of interference patterns"), not holograph ("a document wholly handwritten by the person under whose name it appears"). Laserist The person who performs a live laser show, especially in a planetarium environment. Can also be used for the person who designs and choreographs a pre-recorded show. Laser light show A presentation where laser light is the primary attraction (as opposed to laser special effects). The four main elements of a laser light show are: abstracts, graphics, lumia and beam effects. These may be present in various combinations. A laser show is usually set to music, often with other effects such as theatrical lighting and pyrotechnics. Musical shows are usually divided into a number of song-length modules. Laser special effects Any use of lasers where the laser is not the primary attraction (as opposed to laser light show). For example, a rock band may use complex laser lighting effects comparable to standalone laser light shows. However, because the band itself is the primary attraction, the lasers are considered supporting special effects. Laserium® A registered trademark of Laser Images Inc., referring to their laser light shows. Sometimes used incorrectly as a synonym for any planetarium-based laser light show. Lumia A gauze-like laser effect produced by shining a laser beam through distorting material such as rippled glass. Lumia are often composed of fine parallel lines of light and dark, and they show the characteristic speckle of coherent light. There are many different lumia effects, depending on the type of distorting material. Module A song-length segment of a laser light show. A module is the smallest unit of music-plus-lasers which can artistically stand on its own. A typical planetarium-type laser show is usually made up entirely of different modules. Three-dimensional (3D) laser effects In laser effects, can refer to beam effects or multiple scrim techniques. (In laser graphics, "3D" usually refers to either a 3D graphics database or to stereoscopic projection systems.) Laser beam effects are inherently 3D, filling space with static or kinetic beams. However, these cannot create space-filling objects. Science-fiction films have popularized the misconception that lasers can project large freestanding 3D images. At present, there is no technique which can do this without the image being enclosed in a small volume. One interesting simulation is to project laser graphics through partially translucent screens; a series of these screens can give a floating mid-air effect. This is not true 3D as all images are identical, and merely increase in size with increased projection distance. See also:Three-dimensional laser graphics, Hologram.

Computer Graphics for Laser Shows

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In traditional computer graphics there is an unfortunate lack of agreement over basic terms and concepts. To help avoid this in the laser computer graphics field, ILDA suggests the following terms. Anchor points Additional points placed to help slow the laser beam. Anchor points are usually added at corners and tight curves, to help the scanners accurately follow the desired path. See also:Velocity points. Animation A sequence of frames where each frame is slightly different, giving the illusion of motion. "Animation" refers to the complete group including key frames and tweens. These can be precomputed, such as traditional hand-drawn animations. Or they can be computed in realtime; for example, the single frame of a logo may grow in size and rotate to produce the animation. See also:Key frames, Tweens. Artware Frames and animations used in creating laser modules and shows. Artware can be created by the end user, but the term usually implies "clip art" sold or traded by a third party. This term is preferred over "clip art". See also:Showware. Blanked points Those points in a computer-controlled graphic that are turned off by the blanking device so they cannot be seen. Cel or cell See Frame. Coordinates The placement of a point in Cartesian space; used in laser graphics software. A point at (5,10) is located five units to the right of, and ten units above the origin (0,0). See also:Point. Depth Cueing An effect in 3D graphics where lines appearing further from the viewer are dimmed. This helps enhance the 3D illusion for wireframe images such as those used with lasers. Erase A special effect used in computer-controlled laser graphics. A design disappears point-by-point, as if being erased. The opposite effect is called write out. Frame A sequence of points forming a single, fixed drawing or design. It is analogous to a motion picture frame. The alternative terms "cel" or "cell" are sometimes seen.

Key frames Frames containing the start and end points of action in an animated scene. Intermediate positions are shown in the tween ("in-between") frames. In computer animation, key frames are hand drawn and the computer calculates tweens. In hand animation, the key frames are drawn by the primary animator, while tweens may be drawn by an assistant. Module In a traditional laser show, a module is a song-length segment. It is the smallest unit of music-plus-lasers which can artistically stand on its own. A traditional laser show is usually made up entirely of different modules. In laser computer graphics, a module is a complete set of frames, animations and scenes which can be played back by a user or operator. A laser show can be a single module, but is often a series of modules which have been arranged in sequence. The terms "scene" and "module" express a similar idea: a group of related frames and animations. They differ in that a scene is more of an artistic concept, while a module is more of a technical concept. Point The smallest object which can be manipulated by laser graphics software. Usually includes X (horizontal) and Y (vertical) coordinates, and visibility (on or off) and/or color. Can also include Z (depth), size, shape and other attributes. Computer controlled graphics work by rapidly moving the laser beam from one point to another. The software shows a sequence of points to form a "connect the dots" drawing. See also:Color, Coordinates, Point number, X axis, Y axis, Z axis. Point number The sequence number of a particular point. For example, "point number 1" refers to the first set of coordinates in a point output list. See also:Point.

Precomputed animation In a computer graphics system, a frame sequence which has been hand-drawn, or calculated in a longer time than it takes to play back the animation. As a consequence, every frame is stored in the computer memory, hard drive or similar device. Playback is done by recalling each frame in turn. This is the opposite of realtime animation. Raster graphics Images created by constantly scanning from side to side and up and down - examples include television and computer printers. Most laser projectors do not use raster graphics. This is because a raster graphic spreads the beam's power over the entire screen, making the beam visible only at certain times (as with television). The relatively few laser raster projectors available use high-powered lasers to overcome this problem. An advantage of laser raster projectors is that most can be used to project video, making them powerful television projectors. Non-video laser raster projectors are used to project moving words, giving a look similar to that of a "Times Square" moving lights signboard. Raster graphics are contrasted with vector graphics. Realtime animation In a computer graphics system, a frame sequence which is developed from a source frame in "real time". The manipulations or calculations are completed in less time than it takes to draw the source frame. As a consequence, the source frame plus the manipulation instructions are stored in the computer memory, hard drive, or similar device. Playback is done during the presentation, by recalling the source frame and applying the manipulations. This is the opposite of precomputed animation. Retrace A laser-drawn graphic consists of a series of connect-the-dot points. When all points have been drawn, the laser must return to the first point, to "re-trace" the graphic. The line from last point to first point is the retrace line. Usually, retrace lines are undesired. They can be eliminated by drawing the graphic so the first and last points overlap, or by using a blanking device to block the laser beam during the retrace. Scene A sequence of frames and animations which are lyrically, thematically or temporally related to each other. A lyrically related scene could illustrate the verse or chorus of a song. A thematically related scene could illustrate concepts such as love or events such as boy-meets-girl. A temporally related scene is what we think of as a movie scene: depicting events taking place at a single location during a short time period. Showware All or some of the parts used to create a module or show, such as scripts, computer graphics command programs, or taped audio and control signals. Showware can be created by the end user, but the term usually implies sale or trade by a third party. See also:Artware Three-dimensional (3D) laser graphics In computer laser graphics, usually refers to either a 3D graphics database or a stereoscopic projection system. Can also be applied to 3D volumetric techniques. 3D database Referring to a system of storing height, width and depth information of an object. A 3D computer graphics system can then display a 2D projection of the 3D object drawn from any angle. The resulting projection seems to have depth due to the perspective drawing cues, especially if it rotates or moves. 3D stereoscopic Referring to a method of presenting a viewer with two simultaneous images, a slightly different one for each eye. The brain interprets the parallax cues from the views as if it were looking at a 3D object or scene. (Other non-stereoscopic cues, such as perspective drawing or rotation of a 3D database object, may be simultaneously employed to enhance the effect.) Special glasses are usually used to ensure that each eye is presented a unique view. 3D volumetric Referring to methods which present a 3D image within a volume. This is true 3D in that no glasses are required and the image truly occupies a volume in space. A common technique uses a rotating screen synchronized to the laser output. Usually the 3D volume is small, so volumetric laser displays are currently used only in research and technical applications. See also:Three-dimensional laser effects.

Tweens Individual frames which are part of an animation. The term comes from "in- between". The complete set of tweens plus key frames is an animation. See also:Animation, Key frames. Vector graphics Images created by moving from point to point - examples include handwriting and computer plotters. Most laser graphics are vector graphics. To produce a laser graphic, a computer is first used to draw a series of connect- the-dot points. These are translated to electrical signals and are sent to the scanners. At the projection screen, the moving beam travels from point to point at high speeds, smoothing out the dots. This creates the illusion of a fixed, non- moving image. One limitation is the number of dots which can be drawn before the fast-moving image begins to flicker. With lasers, the practical limit is roughly 1000 points. Vector graphics are contrasted with raster graphics. Velocity points Additional points placed to keep the laser beam scan velocity constant during long excursions. While anchor and velocity points express similar concepts, there are important differences. Anchor points are usually repeated visible points placed to "nail down" the laser beam at sharp turns. Velocity points are usually widely spaced blanked points used to prevent large, uncontrolled jumps as the scanner draws. See also:Anchor points. Write-out A special effect used in computer laser graphics. The laser appears to "write out" a design such as a signature. The opposite effect is called erase. X axis Refers to horizontal (left-and-right) movement of the laser beam. In the ILDA Image Data Transfer format, negative values are to the left, positive values are to the right. See also:Coordinates. Y axis Refers to vertical (up-and-down) movement of the laser beam. In the ILDA Image Data Transfer format, negative values are down, positive values are up. See also:Coordinates. Z axis Refers to movement in front of or behind the viewing plane. (Used primarily with laser graphics software which uses a three-dimensional database.) In the ILDA Image Data Transfer format, negative values are to the rear (away from the viewer), positive values are to the front. See also:Coordinates.

Scientific and Technical Terms

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Lasers can be described in both objective and subjective terms. Objectively, we measure wavelengths, wattage, and brightness. Subjectively, we perceive color, intensity and luminance. The following scientific and technical terms are often used to describe lasers and laser light. Brightness An objective measure of how powerful light is over a specific area. (Specificially, watts per unit area per unit solid angle.) Two lasers can be equal in power; the one with the smaller divergence has higher brightness, since the light is concentrated into a smaller area. Coherence A laser produces coherent light; conventional light sources produce incoherent light. Coherent light waves all travel the same direction (spatial coherence) at the same frequency and in phase (temporal coherence). This gives rise to the very narrow beam and intense, pure light that characterizes laser. Coherence also produces shimmering laser speckle and the web-like effects of lumia. Color A subjective perception of light wavelengths. One of the attractions of lasers is the intense, pure colors they produce. This is because they emit specific, narrow wavelengths of light, which we see as saturated colors. Scientifically, color is the perceived wavelength of light. Different lasers produce different wavelengths or lines, depending on the type of lasing media. Most light-show lasers use gas as the lasing media. Only a few, well-defined lines are emitted by gas lasers with sufficient power to be useful in light shows. These colors cannot be filtered or otherwise modified to produce intermediate colors. This means that only a relatively small number of naturally occurring laser lines are available. To get a wider range of colors, different lines are mixed together using various techniques. Most commonly, red, green and blue lines are individually controlled and combined into a single beam which theoretically can be any desired color. See the section of this Glossary for more information on various color mixing techniques. See also:Line, Wavelength. Divergence An objective measure of the amount that a laser beam spreads as it leaves the laser head. High divergence produces larger spot sizes, which is undesired. Divergence can be a problem when the throw is long. Arrangements of lenses are usually used to minimize divergence in these cases. Flicker A perceptual effect in laser-drawn graphics when the laser cannot complete its path before the eye's persistence of vision sees the image fade. The effect, usually undesired, is that the image is flickering or pulsating. Solutions include fully darkening the environment, changing the laser's power, speeding up the scanning rate, or reducing the complexity of the graphic traced by the laser. A related effect occurs when viewing videotaped laser graphics. The laser's scan rate often does not match the TV camera's frame rate. The video image appears to flicker. Videotaped laser graphics generally exhibit much more apparent flicker than the original live laser graphics. Line Short for "spectral line", referring to a particular wavelength of light in the visible spectrum. See also:Wavelength. Luminance A subjective measure of how brightness is perceived by the eye. It depends not only on brightness but on wavelength. Two lasers can be equal in brightness but a green beam has higher luminance than red, since the eye is more sensitive to green light. Milliwatt One thousand milliwatts equal one watt. Small lasers' beam powers are measured in milliwatts. For example, a 50 mW laser is one-twentieth of a watt; a 500 mW laser is one- half watt.. See also:Watt. Speckle An effect caused by the coherence of laser light. Laser speckle looks like a dense pattern of dark and light areas, which shimmers as you move your head from side to side. The more spread out the laser light on a surface, the more visible the speckle. For example, it is easier to see speckle when viewing lumia than when viewing graphics. Only laser light exhibits this eerie, beautiful iridescence. Watt An objective measure of power; in lasers, usually refers to the optical output power, or strength, of a laser beam. Large light show lasers are generally in the 1 to 20 watt range. Watts are also used in a more conventional sense, to measure electrical power used by a laser. For example, a 10 W (optical) argon laser consumes around 10,000 W of electrical power. Wavelength The distance from the crest of one wave to the next. In lasers, wavelength is important because it determines the perceived color of the light. Visible light has wavelengths extending from about 700 nanometers (red) through orange (~600 nm), yellow (~580 nm), green (~550 nm), blue (~450 nm) and violet (~400 nm). Most gas lasers used in laser display emit many wavelengths, or spectral lines, simultaneously. The lines have different strengths. Usually, only a few lines have significant brightness. For example, an argon laser may produce seven or more lines. The principal lines have wavelengths of 514.5 nm (green) and 488.0 nm (blue); they account for about two-thirds of the laser's total light output. The terms "wavelength", "line" and "color" are often heard when discussing laser light colors. Although there are important technical differences between these concepts, in common usage they are often used interchangeably.

Safety

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The primary hazard of light show lasers is eye damage. Higher power lasers also have some burn and fire hazards. However, no light show laser can do science- fiction type damage or disintegration. Both equipment and show site must be made safe so beams cannot go into the audience. Usually, governmental regulatory agencies must be notified in writing before lasers can be used. Thus far, the regulations have worked well. There have been no reported injuries in the United States from light show lasers since U.S. federal regulations took effect in 1976. All ILDA members active in U.S. laser displays are required to have a current CDRH variance. BMRD The Bureau of Medical and Radiation Devices, a division of Health and Welfare Canada, is the federal government agency which has jurisdiction over laser displays in Canada. Some provinces also have their own regulations and regulatory agencies. A complete list is available from the BMRD. CDRH The Center for Devices and Radiological Health of the Food and Drug Administration, Department of Health and Human Services, is the principal federal regulatory agency covering U.S. laser displays. Some states also have their own regulations and regulatory agencies. A complete list is available from the CDRH. Mask A device used to obstruct the laser beam so it is blocked from undesired areas. The mask is usually placed at the final output aperture of the laser projector. Masks are used for aesthetic reasons, to keep light from going off a screen, and as a safety feature, to ensure lasers cannot reach the audience in case of equipment malfunction. This is also called a beam block. Radiation The CDRH currently requires higher power U.S. lasers to bear labels reading "Warning: Laser radiation". The word "radiation" refers merely to the laser's light. This is not high-energy ionizing "atomic" radiation, which is the more conventional use of the word. The CDRH is considering changing the wording to the more appropriate "Warning: Laser light." Shutter A device used to block the laser's beam. Usually positioned between the laser and the laser projector, so when engaged, no beam reaches the projector or other effects devices. See also:Blanking. Variance Any U.S. laser display viewed by the public must follow CDRH regulations. The regulations cover both laser equipment and the performance site. Permission to vary from the regulations is given on a case-by-case basis, in a document called a "variance". Only very small lasers (5 milliwatts or less) can be used in displays without a variance. Because of the higher power necessary in laser shows, a variance is almost always required. All ILDA members doing laser shows in the United States are required to hold a current CDRH variance. ILDA members outside the U.S. are required to follow the regulations of the location in which they provide laser displays.