You probably have heard the terms “warm white” and “cool white” referring to light bulb colour (or “color” for our American friends). But what does that really mean? And how does it help you select which colour light bulbs you’d prefer for outdoor lighting?

The scale of light colours from red to blue is called the “colour temperature“, and usually expressed in Kelvin, using the symbol K. For instance, a bulb colour might be referred to as “3,000 K”. Lower numbers are “warmer” and higher numbers are “cooler”. In other words, lower numbers are more red, and higher number are more blue.

To illustrate the differences, here are some light sources and their typical matching colour temperatures:

Colour Temperature Example Light Source
1,850 K Sunrise/sunset or a candle flame
2,400 K Incandescent bulbs
2,700 K “Soft white” bulb
3,000 K “Warm white” bulb
4,100 K Moonlight
5,000 K “Cool white” bulb
5,500 K Noon sunlight
6,000 K Direct sunlight
7,000 K Overcast sky
5,500 K Clear blue sky

Those are all typical approximate values, and they all can vary. Also, the colours you see in the chart above will be affected by your monitor settings, ambient colour in the room you’re sitting in now, etc. But the chart gives you an idea of warm and cool colours in relation to each other.

Which colour is best for outdoor lighting? Well, there is no “best”, there’s only what appeals to you personally.

Most people opt for soft white or warm white colours (that is, 2,700 K or 3,000 K) for their outdoor landscape lighting. These warm colours have a hint of firelight in them, and they can feel inviting and attractive. They compliment most stone and hardscape colours, and usually look pleasant against the “Earth tones” you’ll find in most gardens.

Some people prefer a cool white colour, especially if the lighting is more for security or for checking there aren’t any raccoons outside before you let the dog out.

As a rule of thumb, any colour that is cooler/bluer than the ambient light will seem to “pop” or stand out more, which is very good for security lighting but can be a touch stark for general aesthetic lighting. So for outdoor lighting design, colours cooler than moonlight (above 4,100 K) are less typical for landscape lighting.

But it’s all just personal preference, and if you want your lights as bright as possible then choosing a cooler colour can make them stand out more and add to apparent brightness.

One thing to keep in mind is landscape and architectural lights are cast upon subjects that have their own colour: green leaves, red flowers, grey stones, etc. It’s the mix of bulb colour PLUS subject colour that you actually see. Landscape lighting design should take into account the colour that results when the light illuminates an object, not the just colour coming out of the bulb.

The only rule (and it’s really just a rule of thumb) is do not mix lamp colours in your design, at least not without purpose. If some of your lights are 2,700 K and some are 5,000 K then your lighting design might have a patchwork feel to it. It’s typically better to select one colour and use that throughout your landscape. The objects in your landscape will add in their own colours, and the resulting shades will feel more natural.

Incandescent coach lights and warm white up-lights
Click to view full size

If you already have exterior house lights, such as coach lights or the dreaded “pot lights”, then you’ll probably want your landscape lighting to match the colour of your existing bulbs for a seamless effect. The image to the right is a “before” example showing why matching bulbs is important. A quick bulb change later, and the effect was seamless and lovely.

That said, if you just have one or two exterior lights by your door or garage, then if their current colour doesn’t appeal to you it makes more sense to change those few bulbs rather than committing your entire landscape lighting to something less attractive.

Old LED fixtures were notorious for having very blue light, often 7,000 K or above, and that made them very unattractive on landscapes. Low quality LED lamps today can still have that problem, and many (perhaps even most) solar lights still are that unattractive harsh blue. But a quality outdoor lamp will usually be available in a range of warmer colour temperatures.

Unfortunately, just like with their dubious claims of higher and higher lumens, bulb brands can not always be trusted with their colour temperature claims. One brand’s 3,000 K can look different than another’s, and many brands apply the term “warm white” to just about everything under the sun (literally). An outdoor lighting professional can supply you with bulbs that truly match the colour you want. In fact they should be able to come look at your existing bulbs and supply you with matching replacements, or suggest changes for a more attractive effect. But if you’re getting bulbs from a big box store, you might want to buy just a couple to view at night before you commit to a bulk purchase.