CHAPTER 8 - environmentals

Primary source

a luminous source where light energy is generated and transmitted directly to a task.

luminaire

A complete lighting unit consisting of a lamp or lamps, together with the parts designed to distribute the light source and connect it to the power supply. A luminaire is commonly referred to as a fixture.

Footlambert (fL)

A quantitative unit for measuring brightness. Brightness, or luminance, is an index of the intensity of light being emitted, transmitted, or reflected from a surface. The terms brightness and luminance are used almost synonymously. The distinction is that the brightness is the perceived light, while luminance is a measured quantity. Everything visible has some brightness. The. value of a footlambert is 1 lumen per sq foot, which is expressed in the same units as the footcandle. When the illumination is on a surface, the lumens per sq ft are measured as foot-candles. When the brightness is from a surface, the lumens per sq ft are measured as footlamberts. The foot-candles falling on a surface multiplied by the reflection factor or transmission factor of the surface yield footlamberts. brightness often depends on the direction of view, since many surface es exhibit a different reflectance or transmittance at different angles. If a perfectly white, diffuse surface is placed 1 foot from a 1-candlepower source, the brightness of that surface is approximately 1 lumen/ft sq, or 1 footlambert. In sI units, the unit of brightness is the Lambert (L), which is defined as the luminance of a surface reflecting, transmitting, or emitting 1 lumen per square centimeter. Since 1 Lambert is a much larger quantity that is normally encountered, the SI unit commonly used is a millilambert (mL).

Lumen (m)

A quantitative unit for measuring the flow of light energy, which is referred to in the lighting field as luminous flux. In the English system of units, 1 lumen is equal to the luminous flux emanating from 1ft sq of a hypothetical surface all points of which are 1 foot from a uniform point source of 1 candlepower. In SI units, 1 lumen is the luminous flux emanating from 1 m sq of a surface all points of which are 1 m from the 1-candela source. Illumination is the density of luminous flux, expressed as lumens per unit area.

secondary source

Surfaces that derive their brightness from reflected incident illumination. The sun is the ultimate primary source, whereas the moon is a secondary source of light

Refraction

The bending of a ray of light as it passes obliquely through a material.

Glare

The effect of excessive brightness in a field of view, causing annoyance or discomfort and interfering with vision. It may be direct from a light source or reflected from a shiny surface.

Work Station

The immediate contiguous are in which a worker performs visual tasks. This may involve several surfaces, such as a desk, desk return, and table that function as one task location, or a conference table shared by several workers. Normally about 50ft sq is allotted per work station, but the area can exceed that.

Absorbtance

The ratio of light absorbed by a material to the incident light falling on it. All materials absorb some light; darker objects absorb more than lighter-colored objects.

Reflectance, reflection factor, or reflectance coefficient

The ratio of light reflected by a surface to the incident light falling on it. Reflection of light is either specular, diffuse, or some combination of the two.

Transmittance, luminous transmittance, transmission factor, or coefficient of transmission.

The ratio of the light transmitted through a material to the total incident light falling on it. Some materials selectively absorb certain colors more than others. Since those materials may have a different transmittance for each component of light, transmittances are generally used only in reference to the materials that do not selectively absorb. Like reflection, light transmission may be either direct, diffuse, or a combination of the two.

Coefficient of Utilization (CU)

The ratio of the lumens from a luminaire received on a work plane to the lumens emitted by the luminaire's lamp(s). It depends on the particular space as well as on the fixture.

coefficient of beam utilization (CBU)

The ratio of the lumens reaching a specified area directly from a flood light or a spotlight to the total lumens emitted by the beam source

diffuse reflection

The reflected light is scattered in all directions so that the reflecting surface appears equally bright from any angle of view. Any surface with a sandpaper texture reflects light diffusely.

Work plane

The surface on which the visual task is performed and at which the illumination is specified and measured. Unless otherwise indicated, it is normally assumed to be a horizontal plane 30in above the floor.

Diffuse Transmission

The transmitted light is scattered evenly in all directions, appearing equally bright from any angle of view. Light, but no image is transmitted. Materials that transmit light in a diffuse pattern are known as translucent materials. Translucent materials are widely used in light fixtures to diffuse or spread the light evenly in all directions.

Candlepower (cp)

The unit of luminous intensity of a light source. In SI units, it is called Candela (cd). It is an index of the ability of a light source to produce illumination. It always has a directional connotation, such as horizontal candlepower, candlepower at 60 degrees, or spherical candlepower. A typical candle has a luminous intensity in the horizontal direction of approximately 1 candlepower (candela), which is the source of the term. The candela and the candlepower have the same magnitude.

Direct Transmission

This occurs when light passes through clear, transparent materials. The angle at which the light leaves is the same as that at which it enters.

reflector

a device for redirecting the radiant energy of a lamp by reflecting it in a desired direction

refractor

a device for redirecting the radiant energy of a lamp in the desired direction by refraction through a lense.

ballast

a device used with fluorescent and H.I.D. lamps to provide the necessary circuit conditions for starting and operating.

lamp

a generic term for an artificial light source. Incandescent filament lamps are commonly referred to as bulbs, fluorescent lamps are called tubes, and H.I.D. light sources are simply called lamps.

Footcandle (fc)

one lumen of luminous flux spread uniformly over an area of 1ft sq produces an illumination of 1 footcandle. When an SI lumen is spread over 1m sq, the illumination is expressed in lux (lx). footcandles = lumens / ft sq lux = lumens / m sq

specular reflection

sometimes referred to as "regular reflection," this is the kind of reflection observed in a mirror. It is characterized by the angle of reflection being equal to the angle of incident light. At some angle, the image projected by the light source can be seen reflected by the surface. All polished or shiny surfaces reflect light in this manner when the incident ray is directed to the surface at an angle between 45 and 55 degrees from the perpendicular to the surface.

color rendition

the effect of a light source on the apparent color of objects in comparison (consciously or subconsciously) with their apparent color under a reference light source.

efficiency

the efficiency of a luminaire is the ratio of light output (luminous flux) to the light produced by the lamp. the efficacy of a light source is the ratio of output of luminous flux, expressed in lumens, to the power input in watts and is expressed in lumens per watt.

IES

these initials stand for the illumination engineering society of North America, the only technical society on this continent devoted solely to illumination. It prepared and publishes standards, testing procedures, and nomenclature. the IES handbook is the principal authority on these conventions. membership in local chapters and sections is open to anyone interested in lighting.