Browse Definitions:
Definition

candela (cd)

The candela (abbreviation, cd) is the standard unit of luminous intensity in the International System of Units ( SI ). It is formally defined as the magnitude of an electromagnetic field , in a specified direction, that has a power level of 1/683 watt (1.46 x 10 -3 W) per steradian at a frequency of 540 terahertz (540 THz or 5.40 x 10 14 Hz ).

Originally, luminous intensity was measured in terms of units called candles. This expression arose from the fact that one candle represented approximately the amount of visible radiation emitted by a candle flame. This was an inexact specification because burning candles vary in brilliance. So, for a time, a specified amount of radiation from elemental platinum at its freezing temperature was used as the standard. Late in the 20th century, the current definition and terminology were adopted.

The quantities comprising the specification of the candela are obscure to some non-scientists. An EM-field power level of 1.46 x 10 -3 W is small; the radio-frequency (RF) output of a children's toy two-way radio is several times that much. A frequency of 540 THz corresponds to a wavelength of about 556 nanometers (nm), which is in the middle of the visible-light spectrum. A steradian is the standard unit solid angle in three dimensions; a sphere encloses 4 pi (approximately 12.57) steradians.

This was last updated in March 2011

Continue Reading About candela (cd)

Start the conversation

Send me notifications when other members comment.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

SearchCompliance

SearchSecurity

  • copyright

    Copyright is a legal term describing ownership of control of the rights to the use and distribution of certain works of creative ...

  • keylogger (keystroke logger or system monitor)

    A keylogger, sometimes called a keystroke logger or system monitor, is a type of surveillance technology used to monitor and ...

  • password

    A password is an unspaced sequence of characters used to determine that a computer user requesting access to a computer system is...

SearchHealthIT

SearchDisasterRecovery

  • business continuity plan (BCP)

    A business continuity plan (BCP) is a document that consists of the critical information an organization needs to continue ...

  • call tree

    A call tree -- sometimes referred to as a phone tree -- is a telecommunications chain for notifying specific individuals of an ...

  • mass notification system (MNS)

    A mass notification system is a platform that sends one-way messages to inform employees and the public of an emergency.

SearchStorage

  • CompactFlash card (CF card)

    A CompactFlash card (CF card) is a memory card format developed by SanDisk in 1994 that uses flash memory technology to store ...

  • email archiving

    Email archiving (also spelled e-mail archiving) is a systematic approach to saving and protecting the data contained in email ...

  • RAID (redundant array of independent disks)

    RAID (redundant array of independent disks) is a way of storing the same data in different places on multiple hard disks to ...

SearchSolidStateStorage

  • M.2 SSD

    An M.2 SSD is a solid-state drive (SSD) that conforms to a computer industry specification written for internally mounted storage...

  • NVMe (non-volatile memory express)

    NVMe (non-volatile memory express) is a host controller interface and storage protocol to enable a solid-state drive to use the ...

  • SSD RAID (solid-state drive RAID)

    SSD RAID (solid-state drive RAID) is a methodology commonly used to protect data by distributing redundant data blocks across ...

SearchCloudStorage

  • RESTful API

    A RESTful application program interface breaks down a transaction to create a series of small modules, each of which addresses an...

  • cloud storage infrastructure

    Cloud storage infrastructure is the hardware and software framework that supports the computing requirements of a private or ...

  • Zadara VPSA and ZIOS

    Zadara Storage provides block, file or object storage with varying levels of compute and capacity through its ZIOS and VPSA ...

Close