terminology Flashcards
candela, cd
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
color rendering index, CRI
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”
correlated color temperature, CCT
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
current, I
measure of the flow of electricity, expressed in amperes (A)
cut-off angle
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.
efficacy
efficiency of a light source expressed in lumens per watt (LPW or lm/W)
footcandle, FC
a unit of illuminance equal to 1 lumen per square foot
frequency
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
illuminance
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
Kelvin, K
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
light emitting diode, LED
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.
luminaire
a light fixture in its entirety, including a lamp, reflector ballast, socket, wiring, diffuser, and housing
lamp
manufacturered light source. electrically powered lamps are categorized into incandescent (incandescent, halogen) or luminescent lamps (ESL, discharge (flourescent and HID), and SSL(LEDs)
luminance, L
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)
luminous flux
the time rate of the flow of light
lux, lx
unit of illuminance = to 1 lumen per sq meter
luminaire efficiency
ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein
lumens per watt, LPW
Lunen (light) output divided by lamp watts cnsumed (i.e. amount of electricity used); also known as efficacy
mili-candela, MCD
measurement of a light output of a LED in thousandths of a candela
nanometer, nm
a unit of length equal to 10^(-9) meters; commonly used as a unit of wavelength.
power
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)
quality of lighting
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
resistance, R
a measure of resistance to flow of the currrent expressed in ohms
refraction
The process by which the direction of a ray of light changes as it passes obliquely from one medium to another.
