A newer version of the CRI, R96a, has been developed, but it has not replaced the better known Ra general color rendering index.
Lux (lx) is the unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.
This describes the efficiency of an LED light source. For example a 200lm LED chip consuming 3 watts of electricity = 66 lumens per watt. Lumens per watt vary from product to product depending on the LED chip used, how hard the LED chip is being run, and the construction of the fitting and how effective the heat sink is at removing the heat. The latest LED technology is now achieving over 150 lumens per watt.
Lumen output( lm) is the unit of luminous flux, a measure of the total “amount” of visible light emitted by a source. Lumens are related to lux in that one lux is one lumen per square metre. The lumen can be thought of casually as a measure of the total “amount” of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.
The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread.
The lumen can be thought of casually as a measure of the total “amount” of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.
The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread.
The IP Code or International Protection Rating, classifies the degrees of protection provided against the intrusion of solid objects (including body parts like hands and fingers), dust, accidental contact, and water in electrical enclosures. The standard aims to provide users more detailed information than vague marketing terms such as waterproof.
IP – 6 8
First Digit: Solids
Second Digit: Liquids
First Digit: Solids
The first digit indicates the level of protection that the enclosure provides against access to hazardous parts (e.g., electrical conductors, moving parts) and the ingress of solid foreign objects.
0 Not protected No protection against contact and ingress of objects
1 >50mm Any large surface of the body, such as the back of the hand, but no protection against deliberate contact with a body part.
2 >12.5mm Fingers or similar objects.
3 >2.5mm Tools, thick wires, etc.
4 >1mm Most wires, screws, etc.
5 Dust Protected Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact.
6 Dust Tight No ingress of dust; complete protection against contact.
Second Digit: Liquids
Protection of the equipment inside the enclosure against harmful ingress of water.
0 Not protected
1 Dripping water
Dripping water (vertically falling drops) shall have no harmful effect.
2 Dripping water when tilted up to 15°
Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position.
3 Spraying water
Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.
4 Splashing water
Water splashing against the enclosure from any direction shall have no harmful effect.
5 Water jets
Water projected by a nozzle (6.3mm) against enclosure from any direction shall have no harmful effects.
6 Powerful water jets
Water projected in powerful jets (12.5mm nozzle) against the enclosure from any direction shall have no harmful effects.
7 Immersion up to 1m
Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).
8 Immersion beyond 1m.
The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. Normally, this will mean that the equipment is hermetically sealed. However, with certain types of equipment, it can mean that water can enter but only in such a manner that it produces no harmful effects.
In 1986 the Illuminating Engineering Society of North America (IESNA) created the standard LM-63-86, “IES Recommended Standard File Format for Electronic Transfer of Photometric Data.” This has been updated twice, in 1995 and 2002. The IES file is the most common format in North America but is also widely used in Europe. IES photometric data files have the .ies filename extension.
Glare control defines the methodology used in lighting fixture design to reduce the amount of glare caused from the light source within the light fixture. A well designed light fitting will have glare control built into the design of the fitting.
In optics, a diffuser is any device that diffuses or spreads out or scatters light in some manner, to give soft light. Diffuse light can be easily obtained by making light to reflect diffusely from a white surface, while more compact optical diffusers may use translucent objects, and can include ground glass diffusers, teflon diffusers, holographic diffusers, opal glass diffusers, and greyed glass diffusers.
The color rendering index (CRI), sometimes called color rendition index, is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with an ideal or natural light source. Light sources with a high CRI are desirable in color-critical applications such as hospitals, aged care facilities and museums .
Numerically, the highest possible CRI is 100,. Low-pressure sodium lighting has negative CRI; fluorescent lights range from about 50 for the basic types, up to about 90 for the best tri-phosphor type. Typical LEDs have about 80+ CRI, with the newest LED technology achieving up to 98 CRI.
Color temperature is a simplified way to characterize the spectral properties of a light source. While in reality the color of light is determined by how much each point on the spectral curve contributes to its output, the result can still be summarized on a linear scale.
Low color temperature implies warmer (more yellow/red) light while high color temperature implies a colder (more blue) light. Daylight has a rather low color temperature near dawn, and a higher one during the day. Therefore it can be useful to install an electrical lighting system that can supply cooler light to supplement daylight when needed, and fill in with warmer light at night. This also correlates with human feelings towards the warm colors of light coming from candles or an open fireplace at night.
The standard unit for color temperature is Kelvin (K).
Some typical color temperatures are:
|2680 K||40 W incandescent lamp|
|3000 K||200 W incandescent lamp|
|3400 K||Tungsten lamp|
|3400 K||1 hour from dusk/dawn|
|5000-4500 K||Xenon lamp/light arc|
|5500 K||Sunny daylight around noon|
|5500-5600 K||Electronic photo flash|
|6500-7500 K||Overcast sky|
Beam angle indicates the spread of light from a light source and is equally as important as lumen output in downlight fittings. A narrow beam gives a concentrated light which is better for accent lighting. A wide beam gives a more general, softerlight.
A narrow beam would be considered 8-24 degrees, a medium beam, 24-60 degrees and a wide beam from 70-120 degrees.
Lighting Design – The Basics
Most light sources offer two different types of lighting:
The brightest amount of light where the beam directly illuminates an area.
As the direct light bounces off of objects and the environment, it refracts and reflects with more diffused and less powerful rays of light illuminating the surrounding space.
We can look at the beam angle as the cone of direct light coming from its source, and the indirect light as its secondary consequences. The angle of the beam itself is reliant on:
The type of bulb used
The size of bulb used
The type of reflective housing used around the bulb
For the most part you will not have to worry about these issues, as most bulbs have the beam angle on the packaging.
Types of Beam Angle
While almost every conceivable beam angle can be produced, there are standards which are more often used than others. Each standard comes with its own abbreviation and purpose. Let’s now take a look at the most commonly used beam angles, describing their advantages and disadvantages as well as how best to use them.
Specifications: The spot light is commonly abbreviated as SP. It is the narrowest of the common beam angles, with a light beam which spreads out anywhere from 8 to 16 degrees.
Advantages: The spot light is perfect for illuminating an object, or working in conjunction with many other spot lights to light a corridor or hallway in a dimly light scenario such as a bar or nightclub. With such a small beam angle, it can be used to highlight a painting, book case, or even an exterior part of a building such as a window sill or doorway.
Disadvantages: The least versatile of any beam angle. It really can only be used to light a small area or to highlight an object. Depending on the direction, these lights can be harsh on the eyes as the ray of light is very focused. They can also cause problems if used in inappropriate surroundings, especially when a larger beam angle is needed to fully light an environment such as a fire escape.
How to use Them: They can be used as a downlight or uplight, however, they work better when above the subject or area to be lit. They can be placed at a slight angle to create an interesting look, but it is recommended to keep this angle as close to vertical as possible so that it does not shine in people’s eyes.
The luminous intensity data presented in photometric files is useful because it allows lighting designers to observe both the total light output and the angular spread of the light output. The angular information is typically presented as polar diagrams and cone diagrams. Neither of these diagrams is included in the file format itself, but can be generated from the files by using lighting analysis and design programs such as Photometrics Pro, Photometric Toolbox, Relux or Dialux.
The luminous intensity data needed for photometric files is generated by a goniophotometer. A goniophotometer is a mechanical device to support and optionally position the light source (a luminaire or lamp) and a photosensor which measures luminous intensity at each angle, at a set distance. The goniophotometer set-up can be as simple as a manual engineering turntable and a light meter. This has the advantage of being cheap, but the disadvantage of being incredibly time consuming (measuring the previously mentioned 855 angles would take the best part of a day). Most photometric files are generated by an automatic goniophotometer. In this case, the luminaire is mounted to an automatic turning frame, which rotates the device under test through two axes. A measurement of luminous intensity is taken at each angle. The files can be generated by hand but most goniophotometer post processing software generates the files automatically.
In electric lighting, a lot has been said over the years about the importance of maintaining “balance of luminance.” In recent years, the IES’ office lighting recommendations and manufacturers’ literature have promoted the concept of balanced luminance in which room surfaces should be no more than 10 times brighter than the task nor less than one-tenth of the task. Assuming that the average luminance of a computer screen is about 100 cd/m2, this means that the brightest surface of the room should be 1,000 cd/m2 or less, and the darkest should be 10 cd/m2 or greater.
But if the sunlight on the floor near the window is 10,000 cd/m2, is that OK? I suggest that maybe it is and maybe it isn’t, depending on whether the work being done in the space and the overall intent of the design is harmed in some way by the extremes in condition. After all, contrast is drama. While I would hate to have an overly dramatic workspace, I often create borderline-excessive contrast to draw attention to certain aspects of the architecture and to appeal to people’s visual interest, especially for retail and other dramatic types of spaces.
When it comes to daylighting, the extreme contrast of sunlight to the luminance of interior surfaces (whether by natural or electric light) mandates shading. This is not a new issue: throughout history, mankind has learned to shade interiors from direct sun, devising a number of exterior solutions, such as awnings and overhangs, and interior solutions ranging from curtains and sheers to blinds, louvers, and roller shades. Because the sun moves while the structure remains stationary, almost all static shading systems are imperfect. These work well during certain seasons or during certain hours of the day, but they are ineffective during others. Moreover, on cloudy days the shade often is undesirable in order to get enough light indoors. The need for dynamic shading has resulted in a number of clever solutions, from motorized exterior louvers to automated roller shades and blinds.
In the 20th century, improvements in window glass enabled the windows themselves to shade the interior by letting in a controlled amount of direct sunlight. Today, glass can be:
Tinted to absorb a specific amount of light energy. (Note that the absorbed energy becomes heat and will cause the glass to expand, with the threat of cracking.)
Treated with a reflective mirror-like coating, redirecting a portion of solar energy away from the building. Even if the building appears as a mirror, the reflection is not total and a controlled amount of light enters the space.
Coated with a pattern of white reflective ceramic elements called frits. Frits allow some direct light penetration while reflecting unwanted light. Frits are not diffusers—they simply reduce the amount of light equal to the ratio of fritted to unfritted surface area.
All of these treatments allow windows to shade the interior space. Since they are static, they will produce darker interiors on darker days. But this often is a good solution, especially for multi-story buildings with relatively large areas of glass, as the treatments reduce excessive light and heat gain.
Many projects today employ perforated roller shades as a primary means of glare control. The percentage of openness—meaning the density of the weave of the shading material—determines the amount of light penetration and is a function of the visible light transmission of the glass. For instance, from tests performed on the New York Times building, the highly transmittive glass (more than 70 percent) requires 1 percent to 2 percent openness before people find direct sunlight too glaring. If glass with half the transmission (35 percent to 40 percent) were used, the openness could be doubled.
These shades are used on the south, east, and west faces to control direct solar glare; shades on the north side of the structure can be far more open, if they’re needed at all. I typically recommend 10 percent openness on the north façade to reduce the luminance (brightness) of the sky without cutting out all of the light. The best thing about roller shades is that they can be easily automated so that they can be raised to harvest as much daylight as possible on cloudy days.
Strategies commonly employed to reduce unwanted levels of glare include:
Indirect lighting that throws more light upward than downward, diffusing the light and reducing glare .
Parabolic louvers, special lenses or other diffusing media on fixtures that diffuse the fixture’s light output. In an office, it may be possible to de-emphasize the ambient lighting system with reduced light output and diffusing media, while providing adjustable task fixtures at workstations
Relocating the light source
Relocating the task or changing its orientation until the glare is removed
Changing the surface reflectance of the task
Accent lighting is a form of lighting used most commonly for illuminating walks with subtle light. However, this form of lighting can also be used to highlight key objects and focal points in the home or surrounding landscape. For instance, many people like to display particular pieces of artwork or other collectible items in their home. Others may choose to highlight water features or plants in the garden. When adding light to a specific object, it can help create or set a particular mood to the area as well.
Some of the most common accent lighting fixtures include track, recessed and wall-mounted lights. Track lighting is probably considered the most flexible. Fixtures are placed as needed and aimed in any direction along the track. They can also be used with other light sources, like sconces or lamps. Recessed lighting fixtures blend into their surroundings. These are usually installed in ceilings, under cabinets, or within bookshelves and are available in many styles.
Wall-mounted fixtures are attached directly to a wall or similar surface. They can also be placed above or below the frame of a hanging. Outdoors, light fixtures may include those placed in the ground or specialized lamp fixtures. Forms of accent lighting may include low-voltage halogen lights, fiber optics, metal halides, and LED (Light Emitting Diode) lighting.
Halogen lights are great for highlighting or spotlighting objects, as they emit a strong, white light. Fiber optics are good choices for lighting stairs; paths; or water features, like ponds and pools. Metal halides provide soft light and are best used for subtle lighting in small areas. LED lights are becoming more favored. They are more energy efficient, last longer, and are flexible enough for use in various lighting fixtures and situations.
Different types of accent lighting can be used, but path lighting is the most common. Not only does it provide nighttime safety but can also accent interesting patterns, stones, or plants along the way. The use of floodlights can also provide safety. These accents lights are ideal for emphasizing architectural features in the landscape as well. For a more dramatic effect, the use of well lights can be placed in ground or floor fixtures and concealed with plants to cast light upwards.
There is also submersible accent lighting, which is used for creating drama and highlighting ponds or other water features. Backlights are generally placed behind objects to create shadows or silhouettes. All of these types of accent lighting can be used to create various effects with different techniques. For example, silhouetting is used to accentuate an object’s outline. This, as previously stated, is done by placing backlights behind the object and pointing it upwards.
Spotlighting an object involves pointing the lights directly at the intended feature. This popular method is most often used for highlighting focal points in the landscape. Moonlighting can be achieved with recessed light fixtures, which are placed in the ceiling or with floodlights placed in trees. The result is a downward light pattern that mimics natural light from the moon. The type of accent lighting and method used depends on the desired effect to be achieved.