A colour is not only in the cloth. It is in the light.
What we see depends on the light source, the fabric and our eyes. Under the old orange streetlights almost every colour fell to yellow and grey, and even ordinary indoor lamps can make two well-matched pieces drift apart.
AI-generated image, not a photograph of a real person or place.
589 nm the old streetlight colour
Light carries the colour
Fabric picks what it reflects
Eyes do the rest
Check colours in more than one light
THE SHORT ANSWER
Change the light, change the colour.
Fabric can only reflect colours that the light contains. Here is what that means on the street and at home.
ORANGE LIGHT
One colour in, one colour out
Low-pressure sodium streetlights give out a virtually single colour of yellow light. Under them, colours are very hard to tell apart and look like shades of yellow and grey.
Two fabrics can match under one light and not another. This is called metamerism, and blacks, greys, beiges, whites, pinks and mauves are especially prone.
Pick a kind of light to see what it does to the colours of what you are wearing. The bar shows how easy colours are to tell apart.
Based on a National Gallery of Victoria conservation essay, The Naked Scientists, Calderdale Council and RMIT University.
TWO NUMBERS WORTH KNOWING
One narrow colour, one big saving.
Why the old lights drained colour, and one reason councils switched.
589 nm
Where nearly all the light sits
Once warmed up, these lamps glow a strong yellow with spectral lines at 589.0 and 589.6 nm. Under such a narrow band, colours are very difficult to distinguish.
LOW-PRESSURE SODIUM
up to 68%
Energy saving from white LED streetlights
Calderdale Council says its LED lights reduce energy use by as much as 68%, and that the white light improves visibility and colour recognition on the street.
LED UPGRADE · CALDERDALE
Commercial production of low-pressure sodium lamps began in 1932, and the last manufacturer stopped making them in November 2019 (National Gallery of Victoria).
CHECKING A COLOUR MATCH
Look twice, in two lights.
Colour specialists use the same simple habit for fashion and for interiors: compare the pieces under the different lights they will really be seen in.
Gather the pieces
Put the items that must go together side by side: fabric, thread, buttons, zip or the other garments in the outfit.
Look by the window
Check them in daylight first, where the light holds every colour of the rainbow.
Look under your lamps
Then check under the artificial light at home or wherever you will wear them, as matches can break when the light changes.
Watch the tricky shades
Take extra care with blacks, greys, beiges, whites, pinks and mauves, which are especially prone to mismatches.
AI-generated image, not a photograph of a real person or place.
WHY THIS HAPPENS
Three things make a colour.
AI-generated image, not a photograph of a real person or place.
Colour depends on three things: the light source, how the object reflects light, and our own eyes. A blue shirt reflects mainly short wavelengths and absorbs the rest, so if the light has no blue in it, there is nothing blue to reflect.
That is why an orange car indicator does not drain colour the way an old sodium streetlight did. Both look orange, but the indicator's light is a mixture of wavelengths, while the streetlight's is almost pure yellow-orange.
Questions
Questions people ask
Why did everything look orange under old streetlights?
Low-pressure sodium lamps give out an almost single colour of yellow light. Things that reflect that colour look yellow, and things that absorb it have nothing to reflect, so they look grey.
Do white LED streetlights show colours better?
Councils replacing sodium lights say so: Calderdale Council says LED white light makes it easier to distinguish colours and improves visibility on the street.
Why do my black clothes look different outside?
Different dyes can match under one light and not another. RMIT University notes that black garments that match indoors can look reddish, greenish or bluish black outside.
What is metamerism?
When two colours match under one light but not under another. The matching pairs are called metamers, and the mismatch is called metameric failure.
How can I check that an outfit matches?
Lay the pieces together and look at them in daylight and under the artificial light where they will be worn. Buttons, zips and thread made of other materials can look different from the fabric.
