Lawks-a-lawdy, the humble light bulb hasn’t half become more complicated in recent years! Back in the 1980’s, pretty much every ceiling or floor light in your home used a bayonet lamp base, leaving you to select from just a few wattage and shape varieties. Even then, if you weren’t quite sure what to drop into your Homebase, Texas or Great Mills shopping trolley, you could still often plump for a 60W GLS tungsten lamp and be fairly confident of it doing the job. The last blimmin’ thing you had to think about was the light colour.


Today, we have a baffling array of lamp bases and technologies, domestically speaking, although these seem to be thinning down in more recent years outside of any specialist applications. Gone are the tungsten and halogen models and going are the fluorescent types. The GU10 lamp base is the de-facto standard for downlights & spots over the old 4mm 12V MR11 which is now largely extinct, the 5.3mm MR16 which is quickly following suit, and E27 spot lamps such as R50, R63 and R80.

But enough of all that, I could probably write a thousand words just on lamp bases alone and how they’ve evolved over the past thirty years, but this article is supposed to be just about colour temperature – that is the colour of the light your humble bulb is spouting out into your room.

And here’s a handy picture to illustrate the point in order to save me typing a thousand words on this subject.


Colour temperature can make or break anybody’s enjoyment of a newly lit room, so pour a stiff drink and we’ll talk lighting for a few minutes!

When it comes to the colour of light, we refer to its temperature as measured in ‘kelvin’. This is a SI unit for measuring temperature with absolute zero as its zero point; one cannot therefore measure something as being in minus kelvins, nor are kelvins measured in degrees unlike the Celsius or Fahrenheit scales. The term kelvin is also not capitalised, although the SI symbol is ‘K’.

All very interesting perhaps, but what does this all mean when you’re staring in baffling disbelief at the array of different light bulbs on the shelf of Homebase you may well wonder? Well, we can use the kelvin scale to describe where, on the visible light spectrum, any given light bulb is so that we may select the right one for the job.

Traditional tungsten or halogen light bulbs tended to have a ‘warm’ glow, i.e., they would put out a light with a yellowed tinge. This was mainly down to them being better heaters than lamps – 90% of their energy being lost as heat as they burned a filament white-hot. Of course, specially coated or treated models could be sourced for more specialist applications where colour rendering was important, but most of us just bought a basic bulb and accepted the fact it would be a yellow-white light output, and most of us were happy with that as it gave the room a warm and comfortable glow.

Outside of the home, fluorescent lighting was perhaps more prevalent in offices, shops and commercial premsis, and these tended to put out a starker, whiter light. Few homes in the UK employed fluorescent outside of the garage or kitchen, but such luminaires were useful in those areas because they offered a bright, even light and their whiter output made things cleaner and clearer when working either on the broken-down British Leyland jalopy leaking oil all over the garage floor, or on the finer points of knocking up a Crepe Suzette over the breakfast bar.

Although the picture above has quite a wide range of light output on the kelvin scale, in reality you’ll find a narrower range on most shop shelves. Outside of specialist applications such as photography, when buying lighting, you’ll want to look out for the following.

2700 – 3000K Warm White
The most common domesticially, lamps selected in this range will match the traditional light bulbs you’re used to. Switching to these from older tungsten or halogen technologies will see most living rooms and bedrooms illuminated as you’ve been used to seeing them. Stick nearer the 3000K end for a closer match as 2700K or below tends to stray a little too far into the yellow end of the spectrum in my opinion. In fact, drop down to 2000K and you're into the orange sodium territory seen in older street lamps!

4000K Cool White
Often used in commercial lighting to be a better match for the fluorescent lights that have traditionally been employed, and to give good colour rendering both to goods on the shop shelves and to the average office. A clean light without feeling too cold, and often used in the home in kitchens and bathrooms to make them look fresh but not chilly.

5000 - 6500K Daylight White
A cold but crisp light which some would find harsh, but which can be suited for task lighting such as sewing and electronics or for those who have visual impairments where a bright, clear light is beneficial.


It's best not to mix temperatures in the same room as doing so can look odd. If your new kitchen downlights are to be cool white, then the same should be selected for your undercabinet lights to avoid a contrast. If in doubt, stick to warm white colours as that’s what you’ll be most used to domestically. Some lamps or luminaires are colour selectable and can be switched between warm/cool/daylight. This may be via a physical switch setting on the luminaire itself or by a switching sequence such as turning it off and on again in quick succession. Smart bulbs can be controlled via an app to set the colour and brightness on the fly.

One oddity we’ve seen over the years is that men often prefer cool white and ladies warm white. I don’t know if that’s anecdotal or if there’s something in it, but it’s something Nigel and I both agree we’ve picked up on. Personally speaking, I prefer a cool white myself for kitchens, bathrooms, my office, utility room, etc., however I do find warm white is a better choice in the living room when in front of the TV.

Changing the lighting in any given room is always a shock, even if you are retaining the same colour temperature. You’ve likely been used to a commonly used room being illuminated in a particular way for many years, so for it to suddenly alter in any way as you switch out older lamp technologies for newer ones can take one aback. It doesn’t take long for a change to settle in; however, sometimes you just need to live with it for a few days to make the adjustment.