Absorption
This is property of material to convert the radiation they receive (such as light) into different forms of energy, mostly heat. A measure of this property is the degree of absorption a = Fa / F, the ratio of the luminous flux absorbed to the incident luminous flux. (Reflection, Transmittance).
a = Fa / F
 F = incident luminous flux
 Fa = absorbed luminous flux
 Fr = reflected luminous flux
 Ft = transmitted luminous flux
Adaptation
This is the ability of the eye to adjust to changes in luminance by making the pupil larger or smaller. It means we can see correctly across a wide range of illuminance values. The time taken to adapt in this way is largely determined by the luminances at the start and end of the adaptation process. This adaptation takes place very quickly from dark to light (brightness adaptation) but much more slowly (30 minutes or more) from light to dark (darkness adaptation).
Amount of light Q
Unit of measurement: kilolumens per hour [klm/h].The amount of light is the luminous flux emitted by a light source over time.
Black body radiator
Thermal radiation of a material which absorbs all the radiation falling on it depends exclusively on its temperature. The ideal is the lack body radiator It has the highest emissivity of all thermal radiators and its spectral coefficient of emission is 1 (irrespective of temperature and wavelength).
However, as there is no lack body radiator in reality, the closest to it can only be simulated in special laboratories.
The radiation of the black body radiator is defined by Planck's radiation law. This explains how an increasing proportion of the radiation falls in the visible and infra-red spectrums as the temperature increases.
Radiation from a black body (Planckian) radiator
Burning position
The burning position defines the position in which lamps may or may not be operated. A combination of a letter and a number is used in which the letter indicates the datum alignment and the number is the half-angle of the recommended range.
There are three basic datum positions:
h = vertical, base up
s = vertical, base down
p = horizontal
Schematic diagram for burning positions .
Colour rendering
Depending on the location and the purpose, artificial light should enable colours to be perceived correctly as though being seen by natural daylight. Such assessments are based on the colour rendering properties of a light source, which are expressed in terms of the "general colour rendering index" Ra. The colour rendering index is a measure of the comparison between the chromaticity of an object under the light source being measured and its chromaticity under a reference light source.
| Colour rendering property |
Colour rendering group |
Colour rendering index Ra |
Typical lamp |
Excellent |
1 A |
90 |
Tungsten halogen lamps, LUMILUX DE LUXE fluorescent lampsHQI.../D |
Very good |
1 B |
80 - 89 |
LUMILUX fluorescent lamps HQI.../NDL or WDL |
Good |
2 A |
70 - 79 |
Basic fluorescent lamps (25) |
Satisfactory |
2 B |
60 - 69 |
Basic fluorescent lamps (20,23,30) |
Fair |
3 |
40 - 59 |
HQL |
Poor |
4 |
39 |
High-pressure and low-pressure sodium discharge lamps |
The chromaticity of eight (or 14) test colours standardized in DIN 6169 that occur when they are illuminated by the light source being tested are compared with the same test colour when illuminated by the reference light source. The smaller the difference the better the colour rendering property of the lamp being tested. A light source with an Ra value of 100 shows all the colours perfectly, as in the case of the reference light source. The lower the Ra value, the worse the colour rendering.
Test colours for Ra8 |
R1 |
Old rose |
R5 |
Turquoise |
R2 |
Mustard yellow |
R6 |
Sky blue |
R3 |
Yellow-green |
R7 |
Violet |
R4 |
Light green |
R8 |
Lilac |
Additional test colours with saturated colours (Ra14) |
R9 |
Red |
R12 |
Blue |
R10 |
Yellow |
R13 |
Skin tone |
R11 |
Green |
R14 |
Leaf green |
Arc Tube: A completely sealed quartz or ceramic tube where the electrical discharge (arc) occurs and light is generated
Ballast: A device that, by means of resistance, inductance, capacitance or electronic elements, singly or in combination, controls the current, voltage and waveform to the required values for proper lamp starting and operation
Ballast Characteristic Curve: The curve of lamp wattage vs. lamp voltage over a range of normal lamp voltages when a HID ballast is operated at a given supply voltage
Ballast Factor: The ratio of the luminous flux of a lamp on a ballast at the rated supply voltage to the flux on a reference ballast
Ballast Power Factor: Power consumed by the lamp and ballast (watts) divided by the product of line voltage and line current (‘volt-amps’ or ‘VA’); It is a measure of power quality and of concern to utilities
BTL : The distance from ballast to lamp
Burning Position: The position or orientation in which lamps operate
Cold Start Time: The amount of time from the application of ballast voltage to ignition of the arc discharge
Color Rendering Index (CRI or Ra): A measure of a light source’s ability to render colors relative to a standard of 100
Constant Wattage Autotransformer (CWA) Ballast: A magnetic autotransformer lead ballast circuit incorporating a capacitor in series with the lamp; compared to other ballasts, the CWA regulates over a wider input voltage range, holding lamp current nearly constant
Constant Wattage Isolated (CWI) Ballast: A magnetic lead ballast circuit incorporating a fully-isolated secondary winding; it has a capacitor in series with the lamp and the same performance features as the CWA ballast
Correlated Color Temperature (CCT): The perceived "color" of the light emitted by a lamp expressed in Kelvin (K) units
Current Crest Factor: The ratio of the peak-to-rms value of lamp current; metal halide magnetic ballast values range from 1.5 to 1.8
Economic Life: The number of hours a group of lamps will burn before it is economically and aesthetically advisable to group relamp (typically 60% to 75% of rated life)
Efficacy (Lamp): A ratio of lamp lumens to lamp power; measured in lumens per watt (LPW)
Extinction Voltage (North America): The RMS value of supply voltage at which a reference lamp extinguishes when the supply voltage is slowly reduced from its rated value. The ANSI procedure calls for a 2 to 3% reduction in supply voltage per second
Fixture Requirements: The type of fixture a lamp requires; i.e., enclosed or open rated
Formed Body Arc Tube: Precisely reproducible ellipsoidal arc tube formed by pressurizing molten quartz inside a mold; produces arc tubes with higher efficacy and improved color uniformity
HID: High Intensity Discharge lamps; includes metal halide, mercury vapor and high pressure sodium
High-Power-Factor (HPF) Ballast: A ballast designed so that the input power factor is not less than 90% when the ballast is operated at the rated supply voltage using an appropriate reference lamp
High Reactance Autotransformer (HX) Ballast: An autotransformer lag circuit that uses a magnetic shunt path between primary and secondary coils to control reactance; has operating characteristics similar to those of a reactor and has input taps to accept a wide range of supply voltages
Hot Restart or Restrike Time: The time from lamp extinction after a supply voltage interruption to lamp re-start |
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Ignitor: An electronic device which provides, by itself or in combination with other circuit components, the appropriate electrical conditions to start a discharge lamp
Initial Lumens: The light output of a lamp at rated power on a reference ballast after 100 hours of operation
Input Power: See System Power
Lag Ballast: A magnetic ballast having a lagging lamp current with respect to the supply voltage. Current limiting is primarily inductive; holds lamp power reasonably constant with respect to lamp voltage variations
Lamp Power Factor: Power consumed by the lamp divided by the product of RMS lamp volts and RMS lamp current; It is less than unity on magnetic ballasts operating at 50 or 60 hz
Lamp Voltage: The RMS voltage at which lamps operate when they are fully warmed up
Lamp Power: The power consumed by a lamp after warm-up, measured in watts
Lamp Regulation: The ratio of lamp power to lamp voltage often expressed in graphical format
Lead Ballast: A magnetic ballast having a leading lamp current with respect to the supply voltage; current limiting is accomplished by means of an inductor as well as a capacitor connected in series with the lamp; this includes CWA and CWI ballasts
Light Center Length (LCL): The distance from the center of the visible arc discharge to the bottom contact of the base
Line Regulation: The ratio of lamp power to ballast input voltage often expressed as a percentage
Lumens: A measurement of light; takes into account the human eye sensitivity curve so that more weight is given to the yellow-green part of the light spectrum (photopic)
Lumen Maintenance: The lumen output of a lamp at a given operating time or a percentage of 100 hour lumens at that time
Lumens Per Watt (LPW): See Efficacy
Maximum Overall Length (MOL): The maximum allowable distance from the top of the glass bulb to the end contact of the base
Mean Lumens: Light output at 40% of rated lamp life
Normal (Low) Power-Factor (NPF) Ballast: A ballast designed so that the input power factor is less than 90% when the ballast is operated at the rated supply voltage using a reference lamp
Open Circuit Current (Line): The RMS current measured at the input terminals of a ballast with lamp removed or inoperative
Open Circuit Voltage, Ballast (OCV): The voltage across the output terminals of a ballast when no load is connected (RMS, unless otherwise stated)
Open Rated Lamp (Medium Base): Designed for open luminaires; has a narrower neck than standard medium base lamps in order to fit into an exclusionary medium EX26 socket
Open Rated Lamp (Mogul Base): Designed with an extended contact pin on the bottom of the base; should be used with an open fixture mogul sockets (EX39) which prevents electrical contact if a non-O-rated lamp is used
Operating Current (Line): The RMS current measured at the input terminals of a ballast which is operating a reference lamp
Operating Voltage: See Lamp Voltage
Opti-Wave? Ballasts: A Venture lag (magnetic) or electronic ballast designed with a low current crest factor for improved lamp performance. Opti-Wave lag ballasts are also optimized for low open circuit current
Peak Lead Ballast: A CWA ballast that produces a highly peaked open circuit voltage wave shape and a peaked current wave shape
Photopic Light: Describes lumen values measured using the high luminance eye sensitivity function centered at 555 nm (yellow-green) |
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Position Oriented Mogul Base (POMB): Used with horizontal operating lamps; has an alignment pin in the base for proper lamp orientation when installed into a EP39 socket
Power Factor (Ballast): The ratio of the ballast input power (watts) divided by the product of the rms ballast supply voltage and ballast supply current
Pulse Start CWA Ballast: A CWA ballast using an ignitor to start the lamp
Pulse Start Lamp: Specially designed metal halide lamp that requires a high voltage pulse for starting; has improved lumen maintenance
Quint-Volt? Ballast: An Opti-Wave magnetic lag ballast with input voltage taps for five standard voltages - 120, 208, 240, 277 and 480 volts
Rated Life: The number of operating hours at which 50% of most metal halide lamps or 70% of some Uni-Form? pulse start lamps initially started will still be operating
Rated Supply Voltage: The input voltage for which a ballast is designed to operate and to which performance characteristics are referred
Reactor Ballast: A lag ballast with a single input voltage tap
Regulated Lag Ballast: A lag ballast with a third coil for improved lamp power regulation
Restrike: To re-ignite the arc of a HID lamp
Scotopic Light: Describes lumen values measured using the low luminance eye sensitivity function centered at 507 nm (blue-green)
Short-Circuit Current (Ballast): The current at the output terminals of a ballast when the output is shorted (rms, unless otherwise stated)
Shroud: A quartz cylinder surrounding the arc tube of a metal halide lamp; designed to reduce the damage to the outer bulb if an arc tube rupture occurs; usually required to pass the ANSI containment test of the O-rating
Spectral Power Distribution: The distribution of radiant power (watts) of a lamp as a function of wavelength (nm)
Starter: See Ignitor
Starting Current (Line): The RMS current measured through the input terminals of the ballast five to 15 seconds after the lamp has started
Starting Pulse: A high-voltage, low-energy pulse superimposed on the open circuit voltage of some HID ballasts to aid in starting a lamp
Sustaining Voltage: The instantaneous voltage available to the lamp from the ballast at the time the lamp current passes through zero
System Power: The power measured at the input terminals of a ballast while is operating a reference lamp
Tipless Arc Tube: An arc tube made without an auxiliary tube for dosing gases and other ingredients
Warm-Up Time: The amount of time from ignition of the lamp to 90% of full light output
Watts: A measure of energy (in joules) being used or emitted each second
UL "Temp code": An Underwriters Laboratories (UL) alphabetic temperature code for ballasts which designates a range of temperature rise of wire over ambient temperature. The code is found on the label directly following the number 1029X, where X is the appropriate alphabetic character |
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