Electrical Circuits and Lighting
Expert-defined terms from the Professional Certificate in Technology in Lighting Systems course at London School of Business and Administration. Free to read, free to share, paired with a professional course.
Alternating Current AC, RMS, frequency #
Alternating Current AC, RMS, frequency
A type of electric current that reverses direction periodically, typically at 50… #
In lighting systems, AC is the standard supply for most fixtures. Example: A residential lighting circuit draws 120 V AC (North America) or 230 V AC (Europe). Practical application includes feeding fluorescent lamps through electronic ballasts. Challenges arise with voltage fluctuations, which can cause flicker or reduced lamp life.
Ammeter instrument, measurement, current #
Ammeter instrument, measurement, current
A device used to measure electric current in a circuit #
It is connected in series with the load. Example: A digital multimeter set to amperes to verify the current draw of a LED driver. In practice, accurate current measurement is essential for sizing conductors and protective devices. Challenges include ensuring the meter’s burden voltage does not affect the circuit being measured.
Ampere A, current unit #
Ampere A, current unit
The SI unit of electric current, defined as one coulomb of charge passing a poin… #
In lighting design, current determines the load on conductors and the rating of switches. Example: A 120 W incandescent lamp draws 1 A at 120 V. Challenges include calculating cumulative ampacity when multiple fixtures share a single branch circuit.
Arc Lamp high‑intensity discharge, HID, discharge #
Arc Lamp high‑intensity discharge, HID, discharge
A lighting device that generates light by an electric arc through a gas mixture #
Common types include metal‑halide and high‑pressure sodium lamps. Example: A 400 W metal‑halide lamp used in a warehouse. Practical use provides high lumen output and good colour rendering. Challenges involve warm‑up time, ballast compatibility, and potential arc instability leading to flicker.
Ballast driver, starter, regulation #
Ballast driver, starter, regulation
A device that controls the starting voltage and current for gas‑discharge lamps,… #
Two main types: Magnetic and electronic. Example: An electronic ballast for a 18 W compact fluorescent lamp (CFL). Practical application includes reducing power consumption and improving power factor. Challenges include ballast failure, noise, and compatibility with dimming controls.
Beam Angle distribution, optics, lumen #
Beam Angle distribution, optics, lumen
The angle at which a light source emits a specified percentage (commonly 50 %) o… #
Measured in degrees. Example: A recessed downlight with a 30° beam angle concentrates light on a work plane. Practical use influences fixture placement and uniformity. Challenges include selecting the correct angle to avoid glare or insufficient coverage.
Bifurcation branching, wiring, split #
Bifurcation branching, wiring, split
The division of a single electrical circuit into two or more separate paths #
In lighting, bifurcation is used to feed different zones from a common supply. Example: A branch circuit feeding both hallway and lobby lighting. Practical considerations include maintaining balanced loads and proper protection for each branch. Challenges involve voltage drop and ensuring each branch meets code requirements for conductor size.
Circuit Breaker protective device, tripping, overload #
Circuit Breaker protective device, tripping, overload
A switch that automatically opens a circuit when current exceeds a preset value,… #
Example: A 15 A miniature circuit breaker (MCB) protecting a lighting branch. Practical applications include providing selective coordination in multi‑circuit panels. Challenges include nuisance tripping due to inrush currents of LED drivers and ensuring proper rating for fault current levels.
Closed Circuit complete path, loop, continuity #
Closed Circuit complete path, loop, continuity
A circuit where all components are connected, allowing current to flow continuou… #
In lighting, a closed circuit ensures that each fixture receives power. Example: A loop-in wiring system where the feeder and return are tied together at each junction. Practical use simplifies installation. Challenges involve detecting open‑circuit faults that can cause dark spots in a lighting network.
Conductance siemens, reciprocal resistance #
Conductance siemens, reciprocal resistance
The measure of how easily electricity flows through a material, expressed in sie… #
It is the inverse of resistance. Example: A copper conductor with a conductance of 0.01 S per metre. In lighting design, high conductance reduces voltage drop. Challenges include material selection for long runs and temperature effects on conductance.
Contactors relay, switching, coil #
Contactors relay, switching, coil
Electromechanical devices used to switch high‑current circuits, often in lightin… #
They consist of a coil and a set of contacts. Example: A 40 A contactor controlling a bank of LED luminaires. Practical use includes remote switching and integration with building management systems. Challenges involve contact wear, arcing, and ensuring adequate coil voltage.
Cosine Law Lambertian, illumination, angle #
Cosine Law Lambertian, illumination, angle
Describes how luminous intensity varies with the cosine of the angle from the no… #
Light sources approximating Lambertian distribution follow this law. Example: A matte white surface reflecting light uniformly, used in photometric calculations. Practical relevance is in predicting illuminance on work planes. Challenges arise when fixtures have non‑Lambertian optics, requiring correction factors.
Current flow, electrons, amperes #
Current flow, electrons, amperes
The movement of electric charge through a conductor, measured in amperes #
In lighting circuits, current determines the sizing of conductors, protective devices, and switch ratings. Example: A 12 V DC LED strip drawing 2 A per metre. Practical design must ensure that cumulative current does not exceed conductor ampacity. Challenges include accounting for temperature‑dependent current rating reductions.
Direct Current DC, constant polarity, battery #
Direct Current DC, constant polarity, battery
Electric current that flows in one direction only, as opposed to alternating cur… #
Many low‑voltage lighting systems, such as LED strips, operate on DC. Example: A 24 V DC driver powering emergency exit signs. Practical applications include battery‑backed lighting and solar‑powered installations. Challenges involve voltage drop over long runs and the need for DC‑rated protective devices.
Dimming light level control, PWM, TRIAC #
Dimming light level control, PWM, TRIAC
The process of reducing the luminous output of a lighting fixture #
Methods include phase‑cut (leading or trailing edge), pulse‑width modulation (PWM), and analog dimming. Example: A 0–10 V dimmer controlling a bank of fluorescent fixtures. Practical use saves energy and creates ambience. Challenges include compatibility between dimmers and LED drivers, flicker, and maintaining colour consistency.
Diffuser lens, scattering, glare reduction #
Diffuser lens, scattering, glare reduction
A component that spreads light uniformly to reduce glare and create soft illumin… #
Often made of frosted glass or acrylic. Example: A ceiling‑mounted panel light with a diffusing cover. Practical application is in office spaces where uniform lighting is required. Challenges include loss of luminous efficacy due to scattering and potential colour shift.
Edison Screw lamp base, E26, E27 #
Edison Screw lamp base, E26, E27
A standard screw‑type lamp base named after Thomas Edison #
Common sizes include E26 (North America) and E27 (Europe). Example: An incandescent bulb with an E27 base used in a table lamp. Practical relevance is in fixture compatibility and interchangeability. Challenges involve ensuring the socket rating matches the lamp’s voltage and wattage.
Electroluminescent EL panel, thin‑film, AC powered #
Electroluminescent EL panel, thin‑film, AC powered
A lighting technology that emits light when an alternating electric field excite… #
Used in low‑profile backlighting and signage. Example: A 12 V EL panel used as a night‑light strip. Practical benefits include thin form factor and uniform glow. Challenges include limited brightness, short lifespan, and the need for high‑frequency AC drive electronics.
Ferrite Core inductor, magnetic, EMI suppression #
Ferrite Core inductor, magnetic, EMI suppression
A magnetic core made of ferrite material used in inductors and transformers to c… #
Example: A ferrite‑cored choke in the input of an LED driver to suppress high‑frequency noise. Practical application improves power quality and protects sensitive electronics. Challenges include saturation at high currents and added cost.
Fixture luminaire, housing, optics #
Fixture luminaire, housing, optics
The complete assembly that houses a light source, reflector, diffuser, and elect… #
Example: A recessed downlight fixture rated for 15 W LED modules. Practical considerations include mounting method, IP rating, and thermal management. Challenges involve selecting fixtures that match the intended illumination level, colour temperature, and maintenance requirements.
Flux magnetic, phi, induction #
Flux magnetic, phi, induction
In electrical engineering, magnetic flux (Φ) represents the total magnetic field… #
In lighting, the term is sometimes confused with luminous flux, measured in lumens. Example: A transformer core with a flux density of 1.2 T. Practical relevance is in designing inductors for LED drivers. Challenges include avoiding core saturation and managing hysteresis losses.
Fuse protective device, melting, one‑time #
Fuse protective device, melting, one‑time
A sacrificial element that melts when current exceeds its rating, providing over… #
Example: A 5 A slow‑blow fuse protecting a low‑voltage LED driver. Practical use offers simple, reliable protection. Challenges include selecting the correct time‑current characteristic to avoid nuisance blowing during inrush currents.
Grounding earthing, safety, reference #
Grounding earthing, safety, reference
The process of connecting electrical equipment to the earth to prevent electric… #
Example: A grounding conductor bonded to a metal luminaire enclosure. Practical importance is compliance with safety codes. Challenges involve ensuring low‑impedance paths, preventing ground loops, and maintaining continuity during renovations.
Harmonic Distortion THD, waveform, power quality #
Harmonic Distortion THD, waveform, power quality
Deviation of a current or voltage waveform from a pure sinusoid, expressed as a… #
LED drivers and electronic ballasts can introduce harmonics. Example: A 120 V AC circuit with 5 % THD due to multiple LED drivers. Practical impact includes overheating of transformers and nuisance tripping of protective devices. Challenges involve selecting low‑THD drivers and using filters where required.
Incandescent Lamp filament, thermal, warm‑up #
Incandescent Lamp filament, thermal, warm‑up
A lighting device where an electric current heats a tungsten filament until it g… #
Example: A 60 W A‑type incandescent bulb used in a residential ceiling fixture. Practical advantages are simple dimming and familiar colour temperature. Challenges include low luminous efficacy (≈15 lm/W), short lifespan, and high energy consumption, leading to phase‑out in many jurisdictions.
Inrush Current surge, startup, peak #
Inrush Current surge, startup, peak
The maximum instantaneous current drawn by a device when first energized #
LED drivers and fluorescent ballasts exhibit high inrush currents. Example: A 150 W LED driver drawing 10 A for the first 200 ms. Practical considerations include sizing protective devices to tolerate the surge. Challenges involve nuisance tripping of MCBs and the need for soft‑start circuits.
Lumen lm, luminous flux, output #
Lumen lm, luminous flux, output
The SI unit of luminous flux, representing the total amount of visible light emi… #
Example: A 9 W LED bulb producing 800 lm, comparable to a 60 W incandescent lamp. Practical relevance is in comparing light output across technologies. Challenges include measuring lumens accurately and accounting for fixture losses (luminaire efficacy).
Luminance cd/m², brightness, surface #
Luminance cd/m², brightness, surface
A measure of the amount of light emitted or reflected from a surface per unit ar… #
Example: A glossy white panel with 300 cd/m² luminance used as a visual reference in a showroom. Practical use includes evaluating display screens and glare. Challenges involve accounting for viewing angle and surface texture.
Luminous Efficacy lm/W, efficiency, conversion #
Luminous Efficacy lm/W, efficiency, conversion
The ratio of luminous flux (lumens) to electrical power (watts) consumed by a li… #
Example: An LED with 120 lm/W is twice as efficient as a fluorescent lamp at 60 lm/W. Practical importance lies in energy‑saving calculations. Challenges include degradation over time, temperature effects, and the impact of driver losses on overall system efficacy.
Lux lx, illuminance, surface #
Lux lx, illuminance, surface
The SI unit of illuminance, defined as one lumen per square metre. Example #
A workstation requiring 500 lx for adequate task lighting. Practical use determines fixture placement and spacing. Challenges include achieving uniform lux distribution, accounting for ceiling height, and compensating for surface reflectance.
MOSFET switching, semiconductor, driver #
MOSFET switching, semiconductor, driver
Metal‑Oxide‑Semiconductor Field‑Effect Transistor, a semiconductor device used f… #
Example: A buck‑converter LED driver employing a MOSFET to regulate current. Practical benefits include high efficiency and compact size. Challenges involve thermal management, gate‑drive voltage requirements, and protection against over‑voltage.
Neon Lamp gas discharge, signage, low‑power #
Neon Lamp gas discharge, signage, low‑power
A low‑power gas‑discharge lamp that emits a characteristic red #
orange light when voltage is applied across a sealed neon gas tube. Example: A neon “Open” sign used in a retail storefront. Practical applications include decorative signage and indicator lights. Challenges include limited colour options, high operating voltage, and susceptibility to breakage.
Ohm’s Law V=IR, relationship, fundamentals #
Ohm’s Law V=IR, relationship, fundamentals
A fundamental principle stating that voltage (V) equals current (I) multiplied b… #
Example: A 12 V supply powering a 6 Ω resistor draws 2 A (V=IR). Practical use in lighting design includes calculating voltage drop across conductors. Challenges arise when dealing with non‑linear loads such as LED drivers, where resistance varies with voltage.
Photocell photoelectric sensor, daylight harvesting #
Photocell photoelectric sensor, daylight harvesting
A light‑sensing device that changes its electrical resistance based on ambient i… #
Example: A street‑light controller with a photocell that turns lights on at dusk. Practical benefit is energy saving through daylight harvesting. Challenges include sensor placement, calibration, and avoiding false triggers from artificial light sources.
Power Factor PF, cos φ, phase angle #
Power Factor PF, cos φ, phase angle
The ratio of real power (kW) to apparent power (kVA), indicating how effectively… #
A PF close to 1.0 Is desirable. Example: An LED driver with a PF of 0.95 Reduces reactive power demand on the utility. Practical importance includes lower electricity charges and reduced line losses. Challenges involve correcting low PF caused by inductive loads using capacitors or active PF correction circuits.
PWM pulse‑width modulation, dimming, control #
PWM pulse‑width modulation, dimming, control
A method of controlling the average voltage or current by varying the duty cycle… #
Used for dimming LED strips and motor speed control. Example: A 1 kHz PWM signal at 60 % duty cycle delivering 60 % of full brightness. Practical advantages include fine control and compatibility with digital controllers. Challenges include audible noise at low frequencies and potential flicker if the PWM frequency is too low.
Relay electromechanical, switch, coil #
Relay electromechanical, switch, coil
An electromechanical switch that uses an electromagnetic coil to open or close c… #
Example: A 12 V relay controlling a 240 V lighting circuit from a low‑voltage control panel. Practical use includes isolation of control circuits and remote switching. Challenges involve contact wear, arcing, and response time, especially in high‑frequency switching applications.
Resistivity ρ, material property, conductor #
Resistivity ρ, material property, conductor
A material‑specific constant that quantifies how strongly a material opposes ele… #
Example: Copper has a resistivity of 1.68 × 10⁻⁸ Ω·m, making it an excellent conductor for lighting wiring. Practical relevance is calculating voltage drop over long runs. Challenges include temperature dependence (resistivity increases with heat) and selecting cost‑effective alternatives such as aluminium.
Resistor load, ohmic, voltage divider #
Resistor load, ohmic, voltage divider
A passive component that limits current and drops voltage according to Ohm’s law #
Used in LED driver circuits for current sensing or setting reference voltages. Example: A 10 kΩ resistor forming part of a voltage‑divider that sets the dimming level. Practical considerations include power rating (e.G., 0.5 W) and tolerance (±1 %). Challenges involve heat dissipation in high‑power applications and ensuring stability over temperature.
Schottky Diode fast recovery, low forward voltage #
Schottky Diode fast recovery, low forward voltage
A semiconductor diode with a metal‑semiconductor junction, offering low forward… #
Example: A Schottky diode across an LED driver’s output to protect against reverse voltage spikes. Practical benefits include higher efficiency and reduced reverse recovery losses. Challenges include lower reverse voltage rating compared to standard PN diodes and sensitivity to temperature.
Schematic diagram, symbols, wiring #
Schematic diagram, symbols, wiring
A graphical representation of an electrical circuit using standardized symbols t… #
Example: A single‑line diagram showing a lighting circuit with a breaker, conduit, and fixtures. Practical use aids in installation, troubleshooting, and compliance documentation. Challenges include ensuring symbols are up‑to‑date with IEC standards and that the schematic accurately reflects as‑built conditions.
SCR silicon controlled rectifier, thyristor, trigger #
SCR silicon controlled rectifier, thyristor, trigger
A four‑layer semiconductor device that conducts when a gate signal is applied an… #
Used in phase‑control dimmers for incandescent and halogen lamps. Example: A 25 A SCR in a leading‑edge dimmer controlling a bank of 120 V lamps. Practical advantage is robust high‑current handling. Challenges include harmonic generation, limited compatibility with modern LED drivers, and the need for proper snubber circuits.
Surge Protector SPD, transient, protection #
Surge Protector SPD, transient, protection
A device designed to protect electrical equipment from voltage spikes caused by… #
Example: A metal‑oxide varistor (MOV) installed at the mains entry of a lighting control panel. Practical importance is extending the life of sensitive LED drivers and electronic ballasts. Challenges involve selecting the correct voltage rating, ensuring coordination with downstream fuses, and replacing devices after a surge event.
Transformer step‑up, step‑down, isolation #
Transformer step‑up, step‑down, isolation
An electromagnetic device that transfers electrical energy between circuits at d… #
Example: A 230 V to 12 V transformer supplying power to low‑voltage halogen fixtures. Practical applications include providing safe low‑voltage supplies and matching impedance. Challenges include core losses, regulation under varying loads, and ensuring adequate protection against short circuits.
Triac bidirectional SCR, dimmer, phase‑control #
Triac bidirectional SCR, dimmer, phase‑control
A semiconductor device that conducts current in both directions when triggered,… #
Example: A triac‑based dimmer reducing voltage to a 60 W incandescent bulb. Practical benefit is simple integration into AC circuits. Challenges include limited compatibility with LED drivers lacking a dimming front‑end, and the generation of electromagnetic interference.
Voltage V, potential difference, electromotive force #
Voltage V, potential difference, electromotive force
The electrical potential difference between two points, measured in volts #
Determines the energy available to drive current through a load. Example: A 277 V lighting circuit in commercial buildings. Practical design must ensure voltage remains within equipment ratings and accounts for drop across conductors. Challenges involve maintaining adequate voltage under load, especially in long runs, and protecting against over‑voltage transients.
Watt W, power, consumption #
Watt W, power, consumption
The unit of electrical power, representing the rate of energy transfer #
Calculated as voltage multiplied by current (P = V × I). Example: A 15 W LED downlight replacing a 60 W incandescent fixture. Practical use includes energy budgeting and comparing fixture efficiencies. Challenges involve measuring true power consumption of non‑linear loads where apparent power and power factor differ.
XLR Connector audio, DMX, signal #
XLR Connector audio, DMX, signal
A three‑pin circular connector originally designed for audio but widely adopted… #
Example: A DMX controller outputting on an XLR 5‑pin connector to a series of intelligent fixtures. Practical relevance includes robust mechanical locking and shielding against interference. Challenges involve ensuring correct pin assignments, avoiding cross‑talk, and maintaining cable integrity in harsh environments.
Zener Diode voltage regulator, breakdown, reference #
Zener Diode voltage regulator, breakdown, reference
A semiconductor diode designed to operate in reverse‑breakdown mode, providing a… #
Example: A 5.6 V Zener diode used in a LED driver’s feedback loop to set output voltage. Practical benefit is simple, low‑cost voltage regulation. Challenges include power dissipation limits, temperature coefficient, and the need for series resistance to limit current.