The ratio of the radiation absorbed by a surface and the total energy falling on that surface measured as a percentage.

Aluminum

The commonest lightweight metallic element. It is the most abundant metal in the Earth's crust, of which it comprises 8%.

Ambient

Surrounding. Such as; ambient lighting or ambient temperature.

BTU (British Thermal Unit)

Used to measure a quantity of heat. The amount of heat needed to raise the temperature of 1 lb. Water 1° Fahrenheit - One BTU is approximately equal to the amount of heat given off by burning one kitchen match.

Color Rendition

A general expression for the ability of a light source to "bring out" the "true" color of an object.

Color Rendering Index (CRI)

A numerical system of rating color rendering. The sun is considered the ideal and so has a CRI of 100.

Conductance / C factor

The rate of heat flow in BTU's per hour through 1 sq. ft. of any material whether homogeneous or non-homogeneous of whatever thickness or shape resulting from 10° Fahrenheit temperature difference between its 2 exteriors.

Conduction

The direct heat flow through matter resulting from actual physical contact of one part of the same object with its adjoining part. The object may be a gas such as air, or a solid such as iron, lead, etc.

Conductivity k factor

The rate of heat flow in Btu's per hour through 1 square foot of a homogeneous material that will result from a 10° Fahrenheit temperature difference between its two surfaces per inch of thickness.

Convection

One of the three main methods of heat transfer. Convection occurs in a fluid and involves the bodily transfer of fluid molecules.

Dead air space

A confined space of air. A dead air space tends to reduce both conduction and convection of heat. Nearly all insulating materials and systems employ dead air spaces.

Emissivity

The property of emitting heat radiation. All materials emit to some extent.

Emittance

The numerical value of emissivity. Emittance values range from 0.05 (aluminum) to 0.96 for black paint.

Fluorescence

Fluorescence is the property of a material to become self-luminous when acted upon by ultraviolet energy.

Fluorescent Lamp

A low-pressure mercury electric-discharge lamp in which a fluorescing coating (phosphor) transforms some of the ultraviolet energy generated by the discharge into light.

Footcandle

This unit of illumination is defined as one lumen uniformly distributed over an area of one square foot. This means that one footcandle equals one lumen per square foot or 10.76 lux.

Heat

A form of energy that is a reflection of the kinetic energy possessed by atoms and molecules. It is measured in joules, calories or BTUs.

Heat capacity

The number of BTUs a cubic foot of material can store with a 1° increase in its temperature.

Heat gain

An increase in the amount of heat contained in a space, resulting from direct solar radiation and the heat given off by people, lights, and other sources.

Heat loss

A decrease in the amount of heat contained in a space, resulting from heat flow through walls, windows, roof and other building envelope components.

Heat shield

The coating of the outside of a manned spacecraft that dissipates the heat developed during re-entry.

Heat transfer

The transfer of heat, which takes place from a hotter to a cooler body by means of conduction, convection, or radiation, or combinations of them.

Infrared radiation

Electromagnetic radiation, whose wavelength is longer than visible light and lies beyond the red end of the spectrum. We cannot see it, but we can feel it as heat.

Megawatt

A megawatt generally is characterized as sufficient to power 1,000 homes at any given moment.

meter

Equal to 39.37 inches. To convert to inches, multiply by 39.37.

Micron/micrometers

The unit used to measure wavelength. It is equal to a millionth of a meter or .00004 of an inch.

millimeter

One-thousanth of a meter. About the thickness of a paper clip. To convert to inches, multiply by .04.

PIR Sensor

Passive Infrared sensors detect the infrared radiation emitted by the human body to determine if lights are required in a given area.

R factor

Resistance to heat flow: - is the reciprocal of C, k, or U; 1/3, 1/k, 1/U. The smaller the C,k, or U factor fraction and the larger the R factor, the better an insulator.

Radiation

The emission of rays from an object. The sun and the stars give out various forms of electromagnetic radiation, such as light, heat, and radio waves. Radioactive elements give out particle radiation, such as streams of electrons or alpha-particles. In heat physics, radiation is one of the three main mechanisms of heat transfer.

Radiation, infrared

Electromagnetic radiation, whether from the sun or a warm body, that has wavelengths longer than the red end of the visible spectrum. We experience infrared radiation as heat; 49% of the radiation emitted by the sun is in the infrared band.

Resistance - R

R is the reciprocal of conductivity or X/k. (X = thickness of the material in inches)

Reflectance

The ratio or percentage of the amount of light reflected by a surface to the amount incident. The remainder that is not reflected is either absorbed by the material or transmitted through it.

Reflection

The rebound of a wave of energy, such as light and sound, after striking a surface. Mirrors work because of the reflection of light from a silvery surface.

Solar radiation

Electromagnetic radiation emitted by the sun.

Sustainable development

Development that takes care of today's needs without compromising the ability of future generations to meet their needs. Sustained development relies on efficient use of resources, recycling, renewable resouces, restoration, growth management and other measures.

Tensile strength

The stress per unit area of cross-section needed to pull a body apart. It is expressed in such units as newtons per square meter or tons per square inch.

Thermal mass

The amount of potential heat storage capacity available in a given assembly or system. For example, adobe walls, concrete floors, etc.

Thermodynamics

The branch of physics that deals with the interrelationship between heat, work, and other forms of energy and the conservation of energy. Two basic laws of thermodynamics are that energy can be neither created nor destroyed, and that heat cannot flow from a colder to a hotter body.

Thermocirculation

The convective circulation of fluid which occurs when warm fluid rises and is displaced by denser, cooler fluid in the same system.

Thermos flask

One of the first uses of an air space and reflective surface for heat control. A glass container with a double wall, in which there is a partial vacuum. The vacuum prevents heat being transferred by conduction or convection across the gap from the inner way (in contact with the liquid) to the outer. The inside walls of the cavity are silvered to reflect any heat radiated across.

Transmit

(1) To send or forward, as to a destination, dispatch, convey. (2) To emit electromagnetic waves.

Transmittance

The ratio of radiant energy transmitted through a substance to the total radiant energy incident on its surface.

U factor

The rate of heat flow or overall coefficient of heat transmission in BTUs in one hour through one sq. ft. area of the entire depth of ceiling, roof, wall or floor, including insulation if any, which will result from a 10° Fahrenheit temperature difference between the air inside and the air outside.

U value

The number of Btu's that flow through one square foot of roof, wall or floor, in one hour, when there is a 1° Fahrenheit difference in temperature between the inside and outside air, under steady state conditions. The U value is the reciprocal of the resistance or R-factor.

Vapor barrier

A component of construction which is impervious to the flow of moisture and air and is used to prevent condensation in walls and other locations of insulation.