Light Pollution Abatement Site
Calgary Centre
Royal Astronomical Society of Canada
Light Pollution Abatement SiteCalgary CentreRoyal Astronomical Society of Canada |
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TYPES OF LIGHT "BULBS" OR LAMPS
See also the Light and Greenhouse Gases section of this website for more detailed look at different types of lighting and their efficiencies.
Incandescent - is Thomas A. Edison's light bulb, except the carbon filament has been replaced by tungsten wire. This is your ordinary light bulb, like the one in your refrigerator. Light is emitted by the filament when it is heated to a high temperature by electric current. About half of the energy is used to produce infrared light, or heat, so this is not a very efficient light source. As a point source, shielding incandescent light bulbs to prevent glare is easy, but for some reason, shielding is not often done by manufacturers.
An incandescent light bulb.
Mercury Vapour - the familiar bluish white light of these old streetlights rendered many colours a sort of unfamiliar bluish purple hue. Because much of the light emitted is in the ultraviolet part of the spectrum, these lamps are not efficient at turning electricity into visible light. Being a point source, it is possible to design light fixtures that prevent glare, but most of these light bulbs were used in drop-lens semi-cutoff light fixtures (see below). It pays for itself to replace these lights with efficient High-Pressure Sodium bulbs.
Fluorescent - common in stores and many businesses where their energy efficiency makes them a better choice than incandescent. Mercury vapour in the tubes gives off ultraviolet light, which is converted by powdered materials coating the inside of the tube into visible light through fluorescence (hah!, and you thought they just gave these lights a weird name. It's because of the weird process that occurs in them!). Now-a-days, manufacturers have created different coatings that fluoresce in different colours, so no longer must you suffer from ghoulish green skin tones. Fluorescent lamps are quite efficient - most of the initial radiation is ultraviolet with a minimum of infrared (heat) and as long as the coatings are intact, most (but not all) of the ultraviolet light is converted into visible light (another efficient process). So-called black lights are simply fluorescent tubes without the fluorescent material - they emit straight ultraviolet.
Because fluorescent lamps are much more efficient than incandescent lamps, it is tempting to think that they can be left on all the time without worrying about wasting electricity. This is the wrong attitude. Wasted energy is still wasted energy and the issue is that poorly installed fluorescent lamps can create just as much glare and other visibility problems as the incandescent lamps they replace. Outside of commercial use, it is a very rare situation indeed that requires a light on for extended periods.
Common fluorescent tube designs. The upper lamp is designed to directly replace incandescent bulbs, while the lower is the more familiar straight tube design.
Halogen - relatively efficient pure white light makes it a good choice for outdoor lighting where correct colour rendition is important. As a point source, they are easily shielded and focussed to produce a shaped beam pattern and for this reason are the prime choice for most automobile's headlights, replacing the older incandescent light bulbs used prior to the 1980's. They do get hot, indicating some inefficiencies in creating visible light from electricity; in fact, there are halogen heating elements for stoves. Modern indoor halogen "torchiere" light fixtures are required to have a metal safety grating on them because too many drapery fires were started by the hot bulbs.
An example of a halogen outdoor lamp sold as a security light.
Metal Halide - the new kid on the block. A very bright bluish white light commonly seen coming from the headlights of newer expensive imported automobiles. Metal halide is an energy efficient point source lamp.
Low-Pressure Sodium (LPS) - a discharge lamp where the light is produced by radiation from sodium vapour at a relatively low partial pressure. LPS is a "tube source", making it somewhat difficult, but not impossible, to shield it to prevent glare. It is monochromatic light, roughly orange yellow in colour. Because all of the emitted energy is in the visible part of the spectrum, this is a very efficient lamp. However, everything looks various shades of orange yellow; there is no colour rendition. Under a Low-Pressure Sodium lamp, a green car can look the same as a blue one, or a red one.
Low pressure sodium light fixtures at the Calgary Science Centre. Note that the tubes' elongated shape must be accommodated.
The characteristic golden yellow colour of low pressure sodium. This fixture is shielded to put most of the light onto the ground.
High-Pressure Sodium (HPS) - lamp where radiation is produced from sodium vapour at relatively high partial pressures. HPS is essentially a "point source", meaning it can be shielded and focussed efficiently if the manufacturer wishes to. Not as energy-efficient as the Low-Pressure Sodium tube, the HPS lamp's distinctive pinkish-orange colour has just enough blue tones in it to allow you to correctly guess the colour of any car you see at night.
High pressure sodium wall-mounted lamp. Note the colour difference between the HPS light and the background sunlight.
LIGHT FIXTURE TERMINOLOGY
Fixture - the assembly that holds the lamp in a lighting system. It includes the elements designed to give light output control, such as a reflector (mirror) or refractor (lens), the ballast, housing, and the attachment parts.
Luminaire - a fixture with its lamp.
Light Standard - the pole to which the fixture is attached.
Cut off angle, of a luminaire - the angle, measured up from the nadir (i.e. straight down), between the vertical axis and the first line of sight at which the bare source (the bulb or lamp) is not visible.
Full-cutoff fixture - a fixture that allows no emission above a horizontal plane through the fixture.
Sharp Cut-off - the optical design that restricts the distribution of light from the fixture. These restrictions include:
Semi-cutoff fixture - a fixture that provides some cutoff, but less than a full-cutoff fixture. The light source in a semi cut-off luminaire can be seen directly when viewed from the side. Most of the light is placed on the ground, but much is at such low angles that it contributes more to glare than to visibility. Such fixtures are used to cheaply throw light a long ways from the light standard, allowing fewer light fixtures per street. However, good engineering principles commonly indicate that additional full cut-off light fixtures should be used instead. The overly large distance sometimes seen between semi cut-off light fixtures on Calgary streets can lead to problematic situations when retrofitted with full cut-off fixtures when the compromises and shortcuts of the initial streetlight installation become obvious.
This modern light fixture designed to resemble an old time light is a semi-cutoff light fixture.
Lens or Refractor: - controlling light output by means of refraction (lens). More common in older light fixtures, but still used in some good modern designs.
This photograph shows the dispersion of light caused by the sets of angled ribs on both sides of this glass refractor from a semi cut-off light fixture.
Mirror or Reflector - controlling light output by means of reflection (mirror). More and more common in newer designs.
Note the system of angles in the metal reflector of this shoe-box full cut-off light fixture. These separate segments of the metal mirror are used to shape the light beam pattern.
TYPES OF STREETLIGHT FIXTURES
Luminaire - the complete lighting unit, including the lamp, the fixture, and other parts.
Post Top Fixture - any of a number of decorative lighting units where the lamp is directly on top of the vertical post that supports it. Typically, these fixtures have a poor distribution of light beneath the lamp and create glare by shining light sideways. Common examples of post top lights are globe, acorn-style and lantern-style fixtures.
Unusual post-top fixture where the lamp at the top of the metal post shines upward and the light is redirected to the ground by a convex mirror held in place by the transparent box. The light distribution on the ground is low-glare, but since some light bypasses the mirror completely, there is a strong component of uplight, and a brighter bulb than necessary must be used to maintain light levels on the ground.
Globe-Style Light Fixture - a post-top light with a "modern" rounded glass ball enclosing the lamp. Can be fitted with internal louvres or shielded bulbs to reduce glare, but this is commonly not done, so globes are usually glary light fixtures.
Globe-style light fixtures in Calgary. Apart from minor details, these are identical fixtures. Note that the one on the right is not only a post-top design, there are additional lights arrayed along the side of the post.
Close-up of globe-style light fixture showing the small metal shields used to direct the light. In this case, the shields are installed up-side-down, directing the light upwards, away from the street! This increases the contrast between the bright streetlight and the poorly-illuminated street and sidewalk, creating a hazardous situation.
Acorn-Style Light Fixture - a post-top streetlight design with a decorative glass globe that resembles an acorn. These glary light fixtures were initially used with low-output incandescent light bulbs in the first half of the 1900s. Modern examples are typically used with very bright high-pressure sodium or halogen light bulbs and generally render much more glare than other light fixtures.
Acorn-style light fixtures. Such lamp posts evoke simpler times with good reason; they are outdated designs ill suited to modern high output lamps and city-dwellers' 24-hour day.
Lantern-Style Light Fixture - a post-top streetlight or home or yard light designed to resemble an old-time kerosene lantern. Usually used in areas to promote a historic look or charm. While attractive in the daytime, lantern-style luminaires are typically one of the worst designs for nighttime lighting due to their glary nature. Shielded bulbs or internal louvres help immensely.
Lantern-style house light, lantern-style yard light and lantern style streetlight.
Cobrahead Light Fixture - an informal term for the curved-arm oblong-headed fixtures that are mainstay of roadway lighting in Calgary. These are semi cut-off light fixtures in that the refractor distributes most of the light onto the ground, but a significant fraction shines sideways (creating glare) and some shines upwards, never hitting the ground (and thereby causing sky glow).
Cobrahead light fixture that characterises much of suburban Calgary. Note the bulbous refractor that resembles a glass salad bowl.
Closeup of part of cobrahead fixture showing the glass refractor. The '20' denotes that this fixture carried a 200W lamp.
Shoe-Box Light Fixture - an informal term for a rectangular full-cutoff light fixture with a flat glass lens. All of these fixtures are low-glare full cut-off designs.
Shoe-box light fixtures are manufactured by a number of companies. All have a similar compact rectangular shape, a flat glass plate instead of a shaped lens or refractor, and a mirror system inside to shape the beam pattern.
OTHER TYPES OF NIGHTTIME LIGHTING
Security Lighting - this is a broad term used to cover off a number of light fixture types and purposes whose overall stated goal is to improve security and reduce crime. A number of studies now question the effectiveness of light as an inhibitor of crime; lighting with nobody around to view the criminals means that the criminals don't need to remember to bring a flashlight if it is night. Studies show that most home break-ins occur during the day - when people are away at work. Proper lighting can enhance surveillance, but it is unlikely to scare criminals away. Much more information is available in our Light and Crime section of this website.
Task Lighting - this term has been introduced to describe certain types of indoor lighting. Adding lights with a specific job or purpose in mind usually means that the correct light fixture is chosen. For instance, under-cabinet light in kitchens using relatively efficient halogen spotlights or fluorescent tube fixtures means that bright, glare-free lighting is available for food preparation without resorting to overly-bright ceiling fixtures which may just cast shadows under the cabinet overhangs anyway. A proper desk light is another instance of using the task lighting philosophy: think of the job you want done, then find the right light fixture to do it. Outdoors, where the stakes (personal safety, traffic safety) are higher, this type of thinking is needed too.
Wallpack - a light fixture that mounts on the wall and shines light outward and sideways. These are the most commonly used "security light" on commercial premises. Most of these lamps produce a lot of glare because of the mistaken belief that proper outdoor lighting can be achieved by throwing light "over there" from "over here". Wallpacks are commonly a "band-aid" solution, when putting in a light fixture on a pole is thought to be too expensive or too much work.
Three wallpack light fixtures. Note how they are designed to allow light to shine outwards and sideways along the building.
Motion Sensor Lights - use an infrared detector to turns lights on. Used as part of a system to reduce the potential for crime, motion sensor lights are used for two purposes, to draw attention to activity in a normally dark area, and to illuminate the area to allow surveillance by potential witnesses. Motion sensor lights do not fool criminals into thinking that someone just turned on the light - criminals see these lights in the stores, too, so they know what's going on. In better fixtures, the detector can be aimed so that only movement in the selected area causes the lights to illuminate; this reduces false alarms. Some motion sensor lights resemble lantern fixtures. While better than regular lantern fixtures which must remain on all the time, compared to other designs, lantern-style motion detector lights typically produce a lot of glare unless fitted with a special light bulb that is itself shielded to reduce stray light. Look for motion sensor lights with metal shields for the bulbs and fit them with 25 to 60 watt bulbs. Unshielded two-bulb fixtures are typically sold with 75 W or brighter flood lamps. Too much light, like these lamps or halogen fixtures typically produce, only means that nearby unlit areas appear much darker by contrast. Lower wattage regular light bulbs in these fixtures spray glare everywhere and are not a good solution. Unshielded two-bulb fixtures fitted with director bulbs can put light where it is needed without creating glare. See additional discussion in Light and Crime section of this website.
Flood Lights - light bulbs or fixtures designed to direct light evenly over a large area.
Spot Lights - light bulbs (such as director bulbs) or fixtures designed to concentrate light on a specific object. Some manufacturers produce director bulbs with a specific beam divergence (60 degrees, for example), that allows good matching of light source to needs.
Accent Lights - decorative lights used to draw attention to particular features of objects as diverse as plants, trees, or fountains, or buildings. Such lights may be aimed as to accentuate shadows on a textured wall or simply to highlight a particular object at night. It is key to remember that such decorative lights can impact safety and security if they mask steps or ledges or if the light's glare means that a neighbour or homeowner cannot see properly, reducing their ability to keep the property under surveillance for the purposes of reducing crime.
Marker Lights - commonly used on radio transmission towers or along airport runways. Also seen at some shopping malls (Chinook Mall) or on home driveways or sidewalks (low-voltage lighting). Lights should be low brightness and low glare. Many garden lights are too glary to be properly used for this purpose.