The A-Z of lighting language

A familiarity with the technical terms used in architectural interior design really is useful when you start your renovation or redesign project, so here are some technical lighting terms to get you started. The list is alphabetical, feel free to skip to the words you need.

If there are other lighting words or phrases you’d like explained, please drop me a line via my Enquiries form and I’ll add them in to keep this page as useful as possible.

Glossary of technical lighting terms
5 Amp system:

This is a lighting circuit wired to a wall switch just like any other lighting circuit, but used predominately for low level lighting such as table lights. It is, however, possible to wire a standard mains light to the same circuit (for example if you want a focal pendant to come on at the same time as your evening low level lights). For lamps to work on this circuit they need to have their plugs changed to 5 Amp plugs. This is an easy DIY job but it can invalidate warranties so be sure your lamps are working before you change plugs!

Beam width:

This is the angle of the beam of light from the source. The larger the angle, the greater the spread of light and, conversely, the smaller the angle the tighter the beam (like torch light). This term is most used with spotlights where, for example, you may want to highlight a particular feature wall in a wash (from wide spread, multiple sources) or light a sculpture (with a tighter spread, single source). I tend to use a beam width of 30 degrees as standard but if you have a lower ceiling (for example 2200mm), I would recommend going for 46 degrees to flood the light as wide as possible and avoid a harsh, runway feeling. The higher the ceiling the smaller the angle needs to be to have a small spotlight effect.


This is what gets the power to your light. It is not what suspends the light from the ceiling (in the case of a pendant) – it is the electrical source. There are only a few suppliers who have managed to encapsulate the power source within the support wires, so you’ll usually have to contend with a cable. Make sure it is one you like, and make sure it’s long enough for the drop you need!

Colour Correlated Temperature (CCT):

Because LEDs and fluorescent lights do not use heat to create their light, their colour temperature is measured in relation to the colour of the light they emit. CCT should be read as Kelvin (see below) for the purpose of choosing the correct warmth of bulb.

Chain / support wires:

These provide support to pendant lights, independent of the cable. Always check the length they come in matches, or is greater than, the length you need to get your light hanging where you want. Some suppliers will add extra length if requested when ordering.



A circuit is a series of light fittings, controlled simultaneously, for example all downlights (also see Gangs and Multiways).

Colour Rendering Index (CRI):

Colour rendering describes how a light source makes the colour of an object appear to the eye. The colour rendering index (CRI) is a scale from 0 – 100: the higher the CRI, the more accurately colours will be rendered under that light, and so the better subtle colour variations will be seen by the naked eye. Light sources above 85 are considered good for colour rendering, sources above 95 are considered excellent and should be used for jobs needing accurate colour reading. The maximum CRI of 100 is as close to true daylight as currently possible.

However, in what I find an infuriating twist, LEDs are particularly poor at showing red so you may have to go to CRI 99 in an LED to get a high red reading. Red reading is noted in “R”s where R10 is highest red score, and R1 the lowest. If you have objects which have a lot of red (rugs, art etc) you would be wise to check your light source’s R rating to end up with a true read.


A diffuser should be fitted under all open pendants and can also be used as an extrusion cover over LED strips or ropes. It does what it says on the tin, it diffuses the light so that you don’t see the ‘spots’ of the light source, creating a milky overall light effect instead. Make a diffuser a stipulation in your lighting scheme and you’ll never have to see a bare bulb again!


A dimmer system requires its own type of wiring, switch plates, lights and bulbs. It can be cobbled together on existing wiring by changing all other elements but this oftens results in a circuit which ‘buzzes’. Dimmer switch plates are specifically named and needed as they have modules behind the plate which facilitate the dimming. NB: For LED lights you need an LED sensitive mains dimmer module. Try to have no more than ten downlights per circuit to avoid overload, slow light response and “buzzing”.


This type of light fitting casts light downwards and is good to ground a space. Use this type of pendant (always with diffuser!) to avoid shining light on a roughly finished ceiling, or to cast light over an island or dining space.


One gang is the technical switch plate name for one circuit of lights (lets say all the wall lights), two gangs is two circuits (so the wall lights and the pendant). Each circuit has a switch on the switch plate so if you want to buy one switch plate to control two circuits, you will need to buy a ‘2 gang’ plate… think about it as Sharks and Jets – each gang needs it’s own place to fit on the plate.

Glass light fittings:

Glass light fittings can look stunning and work beautifully, but please remember that you will see the bulb. You’ll see it when the light is off and the bulb is at its most passively aesthetic, but most importantly you’ll also see it when the light is on. If you are okay with that that’s great, but some people realise this fact too late. If your light is a pendant, at say 1700mm from FFH (Finished Floor Height), most people will see the bulb at eye height (which, by the way, is within the right range to hang an over island pendant). Consider ceramic fittings as an alternative if you think the bulb might bug you (see the main image for this post as an example).


Ingress Protection (IP):

IP ratings tell you where a light can (or can’t) be used. Bathrooms and outdoors have different codes to tell you which light is suitable and you simply match where you want your light to be to the required code. I’ve also written two short posts dedicated to this subject – click the links at the bottom of this post to be taken to them. NB: A higher rated light (for example, one for outside) can be used in a lower rated area (for example, in a bathroom).

Kelvin (K):

This is a measure of heat energy, or temperature. In lighting, Kelvin measures visible light (colour) temperature. Lower Kelvin colour temperatures mean warmer, yellower light, higher mean cooler, bluer looking light. For reference, 2700K is warm light, 3000K is warm white light, 4000K is cool white light, 6500K is daylight. In a residential environment I specify 3000K as standard as I find it has the correct warmth. To my mind under this runs the serious risk of feeling like an 1800’s tavern. Over, and you are into clinical surgery.

LED Driver:

This controls the current flowing into the light fixture. You should ensure this is provided as part of the fitting, or get a recommendation from the supplier, as it must match the function of the fitting. You should ensure that all the LED chips on a circuit are the same if you are dimming, as they may have a different dim curve if dimmed together – i.e. one dims faster than another.

Light plate:

This is the name for the housing of the switches on the wall that you use to control your lights.


This is the standard unit of Luminous Flux or Lm. In simple terms, lumens indicate the amount of light given by a light source that is visible to the human eye. The higher the number of lumens a light emits, the brighter it is, the lower the number, the less light it emits. Lumens are counted cumulatively by circuit, or by multiple circuits being used at the same time, so you can have many low lumen sources which add up (when used together) to a high light output or high lumen score. One Lm is standardised to equal one candle. Yes, really!

Lumens have come into their own as a measurement of light since LEDs have moved us away from our conventional understanding of light levels from bulbs classified by Watt values. It used to be if you wanted more light you would get a higher Watt (W) bulb. Not so now! For example, a 6.5W LED will deliver the same lumens as a 50W Halogen bulb. How? The advent of technology means that more of an LEDs energy is converted to light rather than lost in heat, compared to a halogen bulb (remember how you used to have to wrap a tea towel around your hand to remove a recently used and blown bulb? Heat!). FYI: The amount of light from an old conventional 60W bulb is around 800-850 lumens.

Multiway / multiple way circuits (also see ‘Ways’ below):

These give you the ability to switch circuits of lights on and off from a number of points (think “There are lots of ‘ways’ of turning this pendant on – at this door here, and over there too…”). Multiway circuits are particularly helpful in rooms which are accessed via a number of routes and in rooms where your requirements change based upon your location within them. For example, if you’d like to be able to switch your bedroom lights off from the bedside, as well as from the entry point to the bedroom, you’d need a multiway circuit


Pendants over islands should hang between 1600-1800mm from FFH (Finished Floor Height) depending on where the bulb hangs in the fitting. Always hang pendants lower than you first think – it is easier to shorten the cable to adjust the height than it is to lengthen it!


These are lights which are placed into the surface of whatever they are on, for example in a cabinetry frame or plasterwork. Note with recessed lights the beam can be obstructed by the edge of whatever it is recessed into.


This is the housing where the light fitting’s electrical cable joins your mains electrics. It is usually circular, and can be made from a variety of materials including plastic, metal and silicone. It normally has a hanging hook within to ensure the light is self supporting, not hanging off the mains wiring (yes, I have seen this!).

Sensor lights:

On occasion rooms may have too many access points to create a switch for all of them – imagine a hallway with several rooms leading off from it. In my experience a successful solution can be to have a circuit of lights on a sensor, activated through movement in the space and preset to turn off after a certain period of time. Sensor lights can also be used outside, as motion detector flood lights for security, or to help light a darker area of the exterior of the house only when it is being used.


Casts light up. These can be used well to show off a vaulted ceiling, or placed at floor level to create a light wash on a textured wall, such as open brickwork.

Up-down light:

(Wait for it.) This casts light both up and down. These are used to highlight two focal points, for example a vaulted ceiling and a feature wall.

Wall lights:

These should be placed between 1650mm and 1800mm FFH (Finished Floor Height) depending on the type of light fitting.

Wall light ‘with plug’ or ‘plugged’:

This is a light such as a side table light, with its own switch and own plug, but one which hangs on the wall (for example the Seletti Monkey Lamp). It is not a mains wired product. These are becoming more popular as a soft fix for wall lighting, or to add drama to a 5 Amp scheme.

Wall light ‘with switch’ or ‘switched’:

This is a wall light which is switched on and off at source, using a switch in the light plate or a pull cord. These are useful as bedside lights where there is no opportunity for a multiway circuit and in bathrooms for a localised light that doesn’t need to be on every time the bathroom is in use.


This word relates to the number of control switches you can use for one circuit: the number of ‘ways’ the lights can be switched on. Coming in from the kitchen? One way to turn the room light on. Also coming from the hall? Another way (so two ways). And so on. NB: You need to know gangs and ways if you are self-sourcing switch plates. Not all manufacturers carry all gangs and ways, so it is best to source your most difficult to find first, then stick with that range to ensure all your plates match.

Thanks for reading, well done getting to the end and remember to send me a message via my Enquiries form if there are other terms you’d like illuminated (sorry, couldn’t resist).

If you would like to learn about how to create a successful lighting scheme, click here to read my article on it, and do feel free to play spot the lighting in the images of on my Featured Projects pages!

Photo credit for first image: Photographer in Residence for Able & Hardie.