Radiant Energy

Energy that travels by waves, particularly electromagnetic radiation. Examples include light emitted by a light bulb and radio waves emitted by an antenna.

Radio Frequency Interference

Abbreviated as RFI.

Electromagnetic radiation emitted by electrical circuits carrying signals as a by-product of their normal operation and which causes unwanted interference in other circuits.

See Ballast > Electromagnetic Interference.

Rapid Start Bulb

"A fluorescent bulb that glows immediately when turned on, and reach full brightness in about 2 seconds." - Advance Ballast Glossary

Rated Life

"the life value assigned to a particular type lamp." (2010) "Nomenclature and Definitions for Illuminating Engineering" ANSI/IES RP-16. ISBN: 978-0-87995-208-2

See Average Life Hours.

Reactive Power

Reactive power exists in an AC circuit when the current and voltage are not in phase.


An outlet is called a receptacle in the National Electric Code (NEC). The NEC defines a receptacle as "a point in the wiring system at which current is taken to utilization equipment." In other words a receptacle can actually take a wide variety of forms. The most common nowadays is the three prong grounded receptacle. However, there are many different receptacles used depending upon the current loads as well as the voltage being supplied.

Recess Fixture

Recess Fixture


One or more electric devices working together that convert AC voltage to DC.

Reference Ballast

A ballast that is designed to provide ideal or "reference" operating conditions for a particular light source. All bulbs that require a ballast for operation are designed with specific power requirements in mind. As such, any product that is manufactured, including ballasts, vary somewhat in performance and output. A reference ballast is an expensive but carefully engineered type of ballast that would be used for example when testing a bulb under laboratory conditions.

Reference Light Source

A light source designed to meet specific criteria for testing purposes. Reference light sources are considered to be the best representation of the particular specification(s) for which they were designed. Examples of specific criteria may be color rendering, color temperature or even specific electrical or thermal (temperature) characteristics. Obviously, these criteria will likely vary depending upon the type of light source being compared and/or the application being tested. Reference light sources are not standard bulbs but are bulbs of a special design and are generally quite expensive.


  • Resistance is a characteristic measured as the degree to which the flow of free electrons (the flow of electricity) is prevented. The resistance of a material can be high due to a lack of free electrons for example. Good conductors such as copper and gold have many free electrons and thus allow electricity to flow easily.
  • Heat increases the resistance of a material by making its atoms vibrate and the hotter the material the more violently the atoms vibrate. In a conductor, which already has a large number of free electrons flowing through it, the vibration of the atoms prevents the straight and smooth flow of the electrons and thus causes the free flowing and stationary electrons to run into each other. Each time they collide it interferes with the flow (uses up energy). These collisions are the basic cause of resistance in conductors.


A device designed to resist the flow of electricity. The manner in which one or more resistors are implemented within a circuit will determine if they will reduce its current, voltage or both. A common example of a resistor in the lighting industry would be a traditional dimmer that is a rheostat type; as the knob is turned the resistance increases and the bulb dims. Another example would be that of a very long wire; all conductors have a resistance value and thus as the length of the wire increases the greater the resistance to the flow of electricity.


The rear portion of the eye that contains, among other things, the photoreceptor cells.

RGB Color Model

The color model comprised of the three primary colors of Red, Green and Blue of the visible spectrum. All colors of light can be made using these three primary colors.


Resistor that permits the value of its resistance to be adjusted.

Root Mean Square

Also known as the quadratic mean.

A type of average, calculated as the square root of the mean of the squares

RYB Color Model

The pigment color model comprised of the three primary colors of Red, Yellow and Blue. All pigment colors can be made using these three primary colors.