terminology

Question 1

candela, cd

Answer 1

measurement unit indicating the luminous intensity (candle power) of a light source in a specific direction. A light source will have several intensities depending on the direction considered

Question 2

color rendering index, CRI

Answer 2

measurement of a light sources ability to render the color of objects “correctly” compared to a reference source with comparable color temperature. scale is 0 to 100, 100 being the most “correct”

Question 3

correlated color temperature, CCT

Answer 3

Generally measures the “warmth” or “coolness” of a light source appearance. specification of the color appearance of a lamp relating its color to that of a reference source heated to a particular temperature and measured in degrees Kelvin

Question 4

current, I

Answer 4

measure of the flow of electricity, expressed in amperes (A)

Question 5

cut-off angle

Answer 5

cut off angle of a luminaire is the angle from the vertical at which a reflector, louver, or other shielding device cuts off direct visibility of a light source. It is the complementary angle of the shielding angle.

Question 6

efficacy

Answer 6

efficiency of a light source expressed in lumens per watt (LPW or lm/W)

Question 7

footcandle, FC

Answer 7

a unit of illuminance equal to 1 lumen per square foot

Question 8

frequency

Answer 8

number of times per second that an alternating current system reverses from positive to negative and back to positive, expressed in cycles per secord or hertz, Hz

Question 9

illuminance

Answer 9

lighting arriving at a surface, expressed in lumens per unit area; 1 lumen per square foot equals 2 footcandle, while 1 lumen per square meter equals 1 lux

Question 10

Kelvin, K

Answer 10

unit of measurement to describe the hue of a specific light source. This is not necessarily related to the heat output of the light source but rather the color of the light output. The higher the Kelvin rating, the more blue the light source is. THe lower the Kelvin rating, the more yellow/amber the light source is

Question 11

light emitting diode, LED

Answer 11

Semiconductor diodes, electronic devices that permit current flow in only one direction. The diode is formed by bringing two slightly different materials together, forming a junction. When a forward voltage is applied, current flow begins and energy is radiated in the form of light.

Question 12

luminaire

Answer 12

a light fixture in its entirety, including a lamp, reflector ballast, socket, wiring, diffuser, and housing

Question 13

lamp

Answer 13

manufacturered light source. electrically powered lamps are categorized into incandescent (incandescent, halogen) or luminescent lamps (ESL, discharge (flourescent and HID), and SSL(LEDs)

Question 14

luminance, L

Answer 14

light reflected in a particular direction; the photometric quantitity most closely associated with brightness perception, measured in units of luminous intensity (candelas) per unit area (square feet or square meters)

Question 15

luminous flux

Answer 15

the time rate of the flow of light

Question 16

lux, lx

Answer 16

unit of illuminance = to 1 lumen per sq meter

Question 17

luminaire efficiency

Answer 17

ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein

Question 18

lumens per watt, LPW

Answer 18

Lunen (light) output divided by lamp watts cnsumed (i.e. amount of electricity used); also known as efficacy

Question 19

mili-candela, MCD

Answer 19

measurement of a light output of a LED in thousandths of a candela

Question 20

nanometer, nm

Answer 20

a unit of length equal to 10^(-9) meters; commonly used as a unit of wavelength.

Question 21

power

Answer 21

the rate at which energy is taken from an electrical system of dissipated by a load, expressed in watts (W); power that is generated by a utility is typically expressed in colt-amperes (V-A)

Question 22

quality of lighting

Answer 22

pertains to the distribution of luminance in a visual environment. the term is used in a positive sense and implies that all luminance contribute favorably to a visual performance, visual comfort, ease of seeing, safety and aesthetics for the specific visual tasks involved

Question 23

resistance, R

Answer 23

a measure of resistance to flow of the currrent expressed in ohms

Question 24

refraction

Answer 24

The process by which the direction of a ray of light changes as it passes obliquely from one medium to another.

Question 25

specular surface

Answer 25

a shiny, highly polished surface which reflects light at an angle = to that of incident light

Question 26

transmission

Answer 26

process by which incident flux leaves a surface or medium on a side other than the incident side, the characterostocs f many materials such as glass, plastics, textiles

Question 27

transmittance

Answer 27

the ratio of the flux transmitted by a medium to the indigent flux

Question 28

voltage, V

Answer 28

measure of the electrical potential expressed in volts

Question 29

watt, W

Answer 29

a unit of electrical power equal to 1 joule per second

Question 30

work plane

Answer 30

The plane at which work usually is done, and on which the illuminance is specified and measured. Unless otherwise indicated, this is assumed to be a horizontal plane 0.76 meters (30 inches) above the floor

Question 31

shielding

Answer 31

A general term to include all devices used to block, diffuse or redirect light rays, including baffles, louvers, shades, diffusers and lenses.

Question 32

lens

Answer 32

A glass or plastic element used in luminaries to change the direction and control of the distribution of light rays

Question 33

lighting design lumens, LDL

Answer 33

number of lumens at 2,000 hours of operation

Question 34

indirect lighting

Answer 34

Lighting by luminaires distributing 90 to 100 percent of the emitted light upward.

Question 35

diffuse lighting

Answer 35

Light that is not predominantly incident from any particular direction.

Question 36

direct lighting

Answer 36

Lighting by luminaires distributing 90 to 100 percent of the emitted light in the general direction of the surface to be illuminated. The term usually refers to light emitted in a downward direction

Question 37

directional lighting

Answer 37

Illumination on the work-plane or on an object predominantly from a single direction