By Gerard Bowtell-Harris, Technical Lighting Specialist, Raylinc Lighting
For most outdoor spaces, Gerard Bowtell-Harris prefers 3000K. The 4000K default survives on council preference, habit and a belief that whiter light helps people see. He treats 4000K as the upper limit for roads and pathways.
Asked whether 4000K is a guideline, a habit or something else, Gerard’s answer is “a little bit of all three.”
Councils decide how their outdoor spaces should look and feel at night. 4000K is also “a bit of an homage to the old metal halide white light.” Many people believe a crisper, more clinical white lets them see better.
Colour temperature is only part of that picture. Colour rendering decides how well you recognise colours, and a 3000K light with good colour rendering shows them well.
Outdoor spaces are full of dim elements. Picture a footpath through a park: green planting on either side, and a sky lit only by the stars and moon.
“I would much rather have a warmer 3000 Kelvin light outside, because it doesn’t detract from those spaces,” Gerard says. Warmer light also cuts blue light scatter, the blue light that hits the ground and reflects back up into the atmosphere.
He accepts this is a topic where opinions differ. His aim is spaces people are comfortable being in.
Go cool enough and you leave compliance behind. “If you’re using, say, a 6500 Kelvin colour temperature, you’re outside of compliance,” Gerard says. In his reading of the standard, 4000K is the limit for pathways and roads.
Very cool light also feels wrong. “Picture daylight happening at night,” he says. Think of an all-night service station lit with blue-tinged white light. It’s uncomfortable to stand under, and that suits a business that wants you in and out quickly.
Sports lighting is the exception. Fittings mounted 20 to 38 metres up run at around 5000K, which suits a very different job.
Gerard sees colour rendering as just as critical, indoors and out. “We don’t want to see a brown car as a black car, or a red car as a brown car,” he says.
For traditional applications, his rule of thumb is a colour rendering index (CRI) of no lower than 70.
Near turtle nesting areas, such as Redcliffe and Bundaberg, designers use habitat lighting. These fittings use much warmer sources, such as 1600K or PC amber. PC amber removes the blue end of the spectrum, so nocturnal animals aren’t drawn to it. Turtles that navigate by moonlight can still find their way.
The trade-off is lower output and poor colour rendering, so the design needs more lights. Gerard says the guidance requires designers to derate the output for these sources. In practice, “you have to design with one hand tied behind your back.”
Gerard’s preference is 3000K for most outdoor spaces. He treats 4000K as the upper limit for roads and pathways, with warmer sources near wildlife habitat.
Partly council preference, partly habit from the metal halide era, and partly a belief that whiter light helps people see.
PC amber is a phosphor-converted amber light source. It removes the blue part of the spectrum and is used near wildlife habitat, such as turtle nesting beaches.
Gerard’s rule of thumb for traditional applications is no lower than 70. Very warm habitat lighting can’t reach that, so designs use more fittings to compensate.
Gerard Bowtell-Harris is a technical lighting specialist at Raylinc Lighting and a member of the Illuminating Engineering Society. He designs lighting for roads, pathways, car parks and facades with consulting engineers.
Contact the Raylinc team to choose the right colour temperature for your next outdoor project.