The lighting industry has undergone significant transformation with the evolution from traditional incandescent and halogen technology to modern LED solutions. This glossary covers essential lighting terminology, from basic concepts like lumens and watts to advanced topics like integrated LED systems and control technologies. Understanding these terms is crucial for both professionals and consumers navigating lighting specifications, energy efficiency ratings, and installation requirements. Special attention is given to LEDs, which have revolutionized the industry with their superior efficiency, longevity, and versatility.

Accent Lighting

Accent lighting is directional lighting used to highlight specific features, objects, or areas within a space. It creates visual interest and depth by drawing attention to architectural details, artwork, plants, or other focal points. Typically three times brighter than the general ambient light in the room, accent lighting often uses adjustable fixtures like track lights, recessed spots, or wall-mounted picture lights.

Ambient Lighting

Ambient lighting, also called general lighting, is the overall illumination that fills a room with soft, diffused light. It provides comfortable background brightness for everyday activities and typically comes from ceiling-mounted fixtures, wall sconces, or natural daylight through windows. The goal of ambient lighting is to create even illumination throughout the space without harsh shadows or bright spots.

Ballast

A lighting ballast is an electrical component that regulates current flow to gas-discharge light sources like fluorescent and HID lamps. It provides the initial high voltage needed to start the lamp and then stabilizes the current during operation. Modern electronic ballasts are more energy efficient and eliminate flickering compared to older magnetic ballasts.

Bayonet Cap

A bayonet cap (B22 or BC) is a light bulb fitting that connects through a push-and-twist motion, using two pins that lock into L-shaped slots. Common in UK and Commonwealth countries, it's an alternative to screw-type (E27) fittings. A smaller version (B15) exists for smaller bulbs.

Bathroom Zones

Bathroom lighting zones are safety-designated areas that determine permitted electrical equipment ratings based on water proximity:

  • Zone 0: Inside bath/shower - IP67 rated only
  • Zone 1: Above bath/shower to 2.25m height - minimum IP44
  • Zone 2: 0.6m around Zone 1 up to 2.25m height - minimum IP44
  • Outside Zones: Normal electrical regulations apply

While an IP65 rating is more commonly used, an IP44 rating is sufficiently high enough for the Building Regulations. IP ratings are explained further.

Beam Angle

Beam angle is the width of a light beam measured in degrees, indicating how focused or spread out the light is from its source. A narrow beam angle (15-35 degrees) creates concentrated, spotlight-like effects ideal for accent lighting, while wider beam angles (60+ degrees) provide broader illumination suitable for general lighting. The angle is measured between the two points where light intensity falls to 50% of maximum brightness.

Bluetooth Lighting

Bluetooth lighting control refers to the wireless technology that allows users to operate LED lights directly from their smartphones through a dedicated app. It enables functions like dimming, color changing, scheduling, and scene setting without requiring a central hub or WiFi connection. Most Bluetooth-controlled LEDs have a typical range of 9-15 metres and can be controlled individually or grouped together for synchronised operation through the manufacturer's mobile application.

Brightness

Brightness refers to the perceived intensity of light output as experienced by the human eye. In lighting specifications, it's typically measured in lumens (total light output) or lux (lumens per square meter at a specific distance). While technically different from light intensity, brightness commonly describes how "strong" or "dim" a light appears and can be adjusted through dimming controls on many modern fixtures. For reference, a standard 60W equivalent LED bulb produces about 800 lumens. A modern A rated energy lightbulb would consume just X and produce Y lumens.

Building Regulations

Building regulations, as they relate to lighting, are mandatory standards and requirements set by governmental authorities to ensure safety, energy efficiency, and proper illumination in buildings. These regulations typically cover:

  • Emergency lighting requirements
  • Minimum light levels for different room types
  • Energy efficiency standards for lighting installations
  • Electrical safety requirements and installation standards
  • Light pollution control measures
  • Accessibility requirements for controls and switches
  • Requirements for natural daylight in occupied spaces
  • Part B of the Building Regulations is for fire safety standards, which advises you when to use fire rated downlights

Bulb

Bulb is the commonly used term for a light bulb, while the more accurate industry term is lamp.

Candela

Candela (cd) is the SI unit for luminous intensity, measuring the amount of light emitted in a specific direction. One candela approximates the light intensity of a single common candle. It's used to calculate beam angles and determine the directional strength of light sources.

Candle

A candle is a lighting unit and historical reference point in lighting measurement, producing roughly 12 lumens of light output. Modern LED "candle bulbs" mimic the shape and warm glow of traditional candles, typically using 2-4 watts while providing 200-400 lumens.

Cap

A cap is the base fitting of a light bulb that connects it to the power source. Common types include:

  • Bayonet (B22/BC) - Push and twist
  • Edison Screw (E27/ES) - Screw-in
  • Small Edison Screw (E14/SES) - Smaller screw
  • Small Bayonet (B15/SBC) - Smaller push-twist

Ceiling Light

A ceiling light is a fixture mounted directly to the ceiling that provides primary ambient illumination in a room. Common types include flush/recessed mounts, semi-flush mounts, surface spotlights, pendant lights, and chandeliers. Most connect to a junction box and are controlled by wall switches.

Colour Rendering Index

CRI (Color Rendering Index) is a measure from 0-100 that indicates how accurately a light source renders colors compared to natural sunlight. A CRI of 90+ provides excellent color accuracy, while lower values can make colors appear distorted or unnatural. Natural daylight has a CRI of 100.

A good example of a high CRI lighting requirement would be in a clothes shop where you want the true colours to be fully visible and not distorted under in-adequate lighting conditions.

Colour Temperature

Color temperature is measured in Kelvin (K) and describes the warmth or coolness of light. Lower values (2700-3000K) produce warm, yellow light similar to sunset. Mid-range (3500-4500K) gives a cooler, more neutral white light. Higher values (5000-6500K) create a more harsh, bluish light resembling daylight.

Compact Fluorescent Lamp

CFL for short, a compact fluorescent lamp is a relic of old lighting technology. They were designed as energy saving alternative to halogen and incandescent, they did produce some effective energy savings of around 80%, but the lumen outputs were misleadingly low. An 11W CFL GU10 was offered as an energy efficient 50W halogen GU10 but wasn't as bright. CFLs contain mercury and eventually got surpassed in record timing with the LED lighting revolution.

Dimmable

Dimmable refers to lights that can be adjusted to different brightness levels using compatible dimmer controls. Not all LED bulbs are dimmable - they must be specifically designed for dimming and paired with appropriate dimmer switches to avoid flickering or damage.

Dimmer Switch

A dimmer switch is a control device that regulates voltage to adjust light output. Modern LED dimmers use either leading-edge (TRIAC) or trailing-edge dimming technology and operate at lower wattages than traditional dimmers. For proper dimming without flickering, buzzing, or premature failure, LED bulbs must be specifically marked as dimmable and paired with compatible LED dimmer switches.

 Skip to the beginning of the images gallery Hamilton Hartland G2 2g 2 Way 100W LED Dimmer Satin Stainless Steel

Downlight

A recessed ceiling fixture that directs light downward. Available as integrated LED units or fixtures accepting replaceable (retrofit) light bulbs (lamps), with the GU19 cap being the most popular choice.

 Play Video Skip to the beginning of the images gallery Collingwood H2 LiteT 4.3W Fire Rated LED Downlight IP65

Edison Screw

An Edison Screw (ES or E27) is a threaded light bulb fitting that screws clockwise into the socket. It's the most common fitting globally, with E27 indicating a 27mm diameter base. A smaller version (E14) exists for decorative bulbs.

Efficacy

Efficacy refers to the efficiency of a light source, measured in lumens per watt (lm/W). It indicates how effectively electrical power is converted to visible light. Higher efficacy means better energy efficiency - LED lights typically achieve 80-100 lm/W compared to 15 lm/W for traditional incandescent bulbs. The latest commercial LED fittings are reaching as high as 180 lumens per watt.

Emergency Lighting

Emergency Lighting consists of battery-powered backup lights that automatically activate during power failures to illuminate escape routes and exits. Building regulations specify minimum illumination levels, duration (typically 3 hours), and placement of these essential safety systems.

Energy Efficiency

Energy Efficiency describes how effectively a light source converts electrical power into visible light while minimizing wasted energy (usually as heat). LED lights are typically 85-90% efficient, compared to incandescent bulbs at 5% efficiency.

Energy Efficiency Label

Energy Efficiency Label is a standardised rating system showing the energy consumption and efficiency class of lighting products on a scale from A (most efficient) to G (least efficient). The label includes power consumption in watts and lumens output. This system was invented in 2012 but got changed in 2021, we've written a dedicated article about energy efficiency labels.

Filament

A filament is a thin wire that glows when heated by electrical current. In traditional incandescent bulbs, it's typically tungsten. Modern LED "filament" bulbs mimic this look with linear arrays of small LEDs.

light bulb example

Fluorescent Lamps

Fluorescent Lamps are gas-discharge lights that use mercury vapor and phosphor coating to produce light. They require ballasts, come in tube or compact (CFL) forms, and are being phased out due to environmental concerns and LED alternatives.

GLS

GLS (General Lighting Service) refers to standard pear-shaped light bulbs traditionally used for general illumination. This classic bulb shape is now available in LED versions that replicate the familiar appearance while offering improved efficiency.

GU5.3

GU5.3 is a bi-pin base fitting for 12V lamps, mainly used in MR16 bulbs. Requires a transformer or driver to convert mains voltage to 12V.

GU10

GU10 is a mains voltage (230-240V) spotlight fitting with a twist-and-lock base. Common in downlights and track lighting, available in LED versions replacing original halogen.

Halogen

Halogen (tungsten halogen) is an incandescent lamp containing halogen gas that enables higher operating temperatures and longer life. Produces bright, white light but very inefficient, converting most energy to heat.

Heat Sink

A heat sink is a component in LED lights that draws heat away from the LED chip to prevent overheating and maintain performance. Usually made of aluminum, proper heat sink design is crucial for LED longevity.

Incandescent

An incandescent bulb is a traditional light source that creates light by heating a tungsten filament until it glows. Very inefficient, converting only 5% of energy to light and 95% lost to heat.

Incandescent Equivalent

Incandescent Equivalent refers to the LED wattage needed to match a traditional incandescent bulb's brightness. Example: "9W LED = 60W equivalent" means the LED produces similar lumens to a 60W incandescent while using only 9 watts.

Integrated LED Downlight

An integrated LED downlight is a recessed ceiling fixture with built-in LED chips rather than replaceable bulbs. Features a driver, heat sink, and optical elements (LED chip) in one sealed unit with typical lifespans of 25,000-50,000 hours. Other fittings such as battens, under cabinet lights and high bays are also available with integrated LEDs. The integrated LED market for commercial lighting is over 90% more popular than retrofit.

IP (Ingress Protection) ratings

IP (Ingress Protection) ratings use two digits to indicate protection against solid objects and water. First digit (0-6): dust protection. Second digit (0-8): water protection. Example: IP65 is dust-tight and protects against water jets.

Lamp

Lamp has two meanings in lighting:

  1. A technical term for the light source itself (the bulb)
  2. A complete lighting fixture, typically portable and placed on tables or floors

The term originated from oil-burning light sources but now applies to all types of lighting devices.

Leading Edge

Leading-edge dimming (also called TRIAC or forward-phase) is a dimming protocol that cuts power at the beginning of each AC wave. It's commonly used with traditional incandescent bulbs but may cause flickering with LEDs unless specifically compatible.

LED

An LED is a semiconductor device that emits light when electrical current passes through it. LEDs offer high efficiency (80-90%), long life (25,000+ hours), instant-on operation, and excellent color options. They produce minimal heat and contain no mercury. Shuji Nakamura invented the first bright blue LED in 1994 while working at Nichia Corporation. This breakthrough enabled white LEDs for general lighting, as blue LEDs could be combined with yellow phosphor to create white light. He shared the 2014 Nobel Prize in Physics with Isamu Akasaki and Hiroshi Amano for this achievement.

LED Driver

An LED driver is an electronic device that regulates power to LED lights. It converts AC to DC power and provides constant current/voltage, protecting LEDs from power fluctuations. Unlike simple transformers, drivers actively manage power delivery for optimal LED performance.

LED Profile Rails

LED profile rails (also called aluminum channels or extrusions) are mounting systems for LED strip lights. They provide heat dissipation, protect the strips, and often include diffusers to create smooth, professional lighting effects.

Life Expectancy

Life expectancy (or rated life) indicates how long a light source is expected to function before significant light loss. For LEDs, typically rated 10,000-50,000 hours, measured to L70 (when output drops to 70% of initial brightness).

Lighting Controls

Devices that adjust light output, including switches, dimmers, sensors, and smart systems.

Lumen

Lumens is the total amount of visible light emitted by a source. For reference: a 60W equivalent LED bulb produces about 800 lumens. A 5W GU10 LED produces around 400 lumens, which is comparable to a 50W halogen. There are two different types of lumens to consider which are:

  • Total lumens - the raw light output from the source
  • Useful lumens - the actual light output that reaches the target area after accounting for fixture/diffuser losses

This is supposed to helps consumer understand real-world performance versus raw output. But it often provides further confusion as manufacturers don't easily declare and define each value. Ultimately, you want to purchase an LED with a certain lumen output, with this value matching the packaging and the performance.

Luminaire

A luminaire is a complete lighting unit, including the light source, fixture housing, electrical components, and optical elements that direct and distribute light. If you're measuring the wattage of a luminaire you consider the total wattage of the LED driver or ballast.

Microwave Sensor

A microwave sensor detects movement using high-frequency electromagnetic waves, controlling lights based on motion and presence. Unlike PIR sensors, microwaves can detect movement through thin walls and work in high temperatures.

MR16

MR16 is a low-voltage reflector bulb with a bi-pin (GU5.3) base, typically 12V. Standard diameter 50mm (2 inches), used in track and recessed lighting. Now available in LED versions replacing traditional halogen. Some manufacturers used to call a GU10 halogen an MR16 but this term is predominantly used for low voltage reflector lamps. The low voltage 50W halogen made recessed downlights very popular due to their ultra clear, high CRI light output. Although energy inefficient the halogen light produces exceptional lighting results.

OLED

OLED (Organic Light Emitting Diode) is a lighting technology using organic semiconductors. Creates extremely thin, flexible light panels that can be transparent when off. Currently expensive but offers unique design possibilities.

PAR

PAR (Parabolic Aluminized Reflector) refers to a lamp shape with a precision reflector directing light in a controlled beam. Common in track lighting and outdoor fixtures, specified by diameter (PAR16, PAR20, PAR30, PAR38). These type of lamp mainly had an E27 cap but some also had the B22 Bayonet cap.

Pendant Light

A fixture suspended from the ceiling by a cord, chain, or rod. Popular over dining tables, kitchen islands, and in entryways. Available in single drops or multi-light clusters.

PIR

PIR (Passive Infrared) sensor detects motion through heat changes, automatically controlling lights when people enter or leave a space. Common in security lights and energy-saving applications.

Retrofit Lamp

A retrofit lamp is a modern LED bulb designed to replace traditional light sources while using existing fixtures and fittings. Preserves original fixture appearance while providing LED benefits of energy efficiency and longer life.

SELV

SELV (Safety Extra-Low Voltage): Operating voltage below 50V AC or 120V DC, reducing electric shock risk. Common in LED drivers and bathroom lighting zones.

Solar Powered Lighting

Solar Power is a renewable energy source using sunlight to generate electricity. In lighting, solar-powered fixtures use photovoltaic cells to charge batteries during daylight for nighttime illumination.

Spotlights

A spotlight is surface mounted light fixture that has a directional angle of light. Many consumers use the term spotlight to describe a recessed downlight or are a GU10 lamp but spotlights are light fittings. They available in different finishes and styles with either one or multiple spotlights. One advantage of using a spotlight is that you can direct the angle of light to any area of your room. Common types include GU10 (mains voltage) and integrated LED spotlights.

Task Lighting

Focused, directional lighting for specific activities like reading, cooking, or desk work. Usually brighter than ambient lighting and positioned to eliminate shadows on the work surface.

Track Lighting

Adjustable light fixtures mounted on a continuous track that provides power. Allows fixtures to be positioned anywhere along the track for flexible accent and task lighting.

Track lights are positioned onto a length of metal track which has an input power. The track spotlights can be moved around the track, allowing you to direct the lights onto the optimal angle. Track lighting is available in kits or as individual components. You usually require a length of track, a mains input connector, a dead end and a track light. Track lights are available in GU10 or integrated LED versions.

Trailing-Edge Dimming

Trailing-edge dimming (or reverse-phase) cuts power at the end of each AC wave. It's the preferred dimming method for LED lights, providing smoother control with less flicker than leading-edge.

Transformer

Transformers converts mains voltage to a lower voltage but only the voltage is converted not the current. Generally used in AC (Alternating Current) products and don't convert to DC (Direct Current) for LED lights. Input voltage is mains 230V, with output voltage of 12V AC. Using these incorrectly with MR16 LEDs, which isn't always clear can result in product failure.

Voltage

Voltage is the electrical potential difference that drives current through a circuit. Common three types:

  1. Mains: 230-240V (UK/EU) or 120V (US)
  2. Low voltage: 12V or 24V (common in LED systems)
  3. Extra-low voltage (SELV): Below 50V AC/120V DC for safety

Watts

Watt (W) measures electrical power consumption. LED technology drastically reduces power needs: a 5W LED equals a 50W halogen (400-450 lumens), while a 2.3W A Rated LED matches a 40W traditional bulb (485 lumens). This represents up to 90% energy savings for the same light output.

The latest A rated LEDs can be as much as 50% more energy efficient than earlier LEDs, but when you're down to just a watt or two, the energy saving net value is minimal.