When it comes to reflecting heat, not all colours are created equal. Some colours absorb more heat from sunlight than others, causing surfaces painted those colours to get hotter. Knowing which colour reflects the most heat can be useful for everything from choosing the paint for your house exterior to picking out clothing that will keep you cool on a hot summer day.
How Light and Colour Work
To understand which colours reflect the most heat, it helps to first understand a bit about how light and colour work. Sunlight, also known as visible light, contains a spectrum of different wavelengths that our eyes perceive as different colours. The longest wavelengths appear red while the shortest wavelengths appear violet, with orange, yellow, green, blue, and indigo falling in between. An object’s colour depends on which wavelengths it absorbs and which it reflects.
For example, a leaf looks green because it contains chlorophyll pigments that absorb blue and red light but reflect green light back to our eyes. White objects reflect nearly all visible wavelengths equally while black objects absorb most of the light that hits them.
When sunlight hits an object, some of that visible light gets converted to heat. The more light an object absorbs, the more it heats up. Darker colours absorb more sunlight than lighter ones, which is why wearing black clothing on a hot day can make you feel even hotter.
How Colour Affects Heat Absorption
Many factors influence how much heat a colour absorbs from sunlight. Here are some key considerations:
- Dark vs. light colours – Darker colours absorb more light across the visible spectrum compared to lighter shades of the same hue.
- Wavelength – Longer wavelengths like red and orange are more likely to be absorbed and converted to heat compared to shorter wavelengths like blue and violet.
- Glossy vs. matte finish – Glossy or shiny surfaces reflect more light while matte or textured finishes absorb more.
- Material and pigments – The chemical composition of dyes, pigments, and base materials impacts light absorption.
In general, darker colours made with pigments that absorb longer visible wavelengths will heat up the most in sunlight. Lighter colours made with reflective materials and short-wavelength absorbing pigments stay coolest.
Reflective Properties of Different Colours
Here’s a more in-depth look at how some common colours compare in their heat reflective abilities:
White
White reflects nearly all visible light wavelengths equally. With a highly reflective surface, most sunlight bounces off rather than being absorbed as heat. White objects stay cooler in the sun as a result. A white roof or exterior paint colour can lower indoor temperatures in hot weather.
Yellow
Yellow absorbs some light from the green to violet portion of the spectrum but reflects longer red and orange wavelengths. On the visible spectrum, it falls between high energy violet and low energy red. Yellow reflects about 60% of sunlight, absorbing the remaining 40% as heat. It stays cooler than darker colours but warmer than white.
Red
Red objects reflect red light strongly but absorb other visible wavelengths. Longer red wavelengths carry less energy than shorter violet and blue ones, so red reflects less heat than darker colours. However, red dyes contain pigments that readily absorb green to violet light and convert it to heat. Red reflects about 40% of sunlight.
Green
Green objects absorb red and blue light, reflecting mostly green wavelengths. Green sits in the middle of the visible spectrum in terms of energy. It absorbs about 45% of sunlight as heat, making it hotter than lighter shades like yellow and cooler than darker reds.
Blue
Blue absorbs longer orange, red, and yellow wavelengths while reflecting short violet and blue wavelengths. It absorbs about 50% of sunlight as heat. While not as cool as white or light yellow, blue stays cooler than colours like red, purple, and black.
Black
Black absorbs almost all visible wavelengths. Little light reflects off black surfaces, allowing over 90% of sunlight striking it to be converted to heat. Black clothing, cars, and roofs can reach extremely high temperatures in the sun.
Chrome or Silver
Polished or chrome-plated metals have a shiny, mirror-like finish that reflects up to 90% of sunlight depending on quality. However, while chrome looks silver, it doesn’t reflect as well as actual silver metal plating. Silver reflects up to 95% of sunlight, keeping it cooler than any colour paint.
Research on Heat Reflectance by Colour
Scientific studies have quantified the solar heat reflectance of various colours by measuring surface temperatures or absorption of ultraviolet, visible, and infrared radiation. Here are some research findings:
- One study found black paint absorbs up to 96% of sunlight as heat, compared to 4-15% absorption for white paint. Black surfaces reached over 30°C hotter than white in direct tropical sunlight.1
- Red brick can absorb up to 85% of solar radiation, while white marble reflects over half the sunlight striking it.2
- A test of coloured aluminum panels found black absorbed 97% of radiation, whereas white paint reflected over 80% of sunlight. Red, green, and blue paints absorbed 75-80% of radiation.3
- White polyester fabric was measured absorbing 16% of UV rays and 42% of heat. Black polyester absorbed over 95% of UV and 90% of heat.4
While exact numbers vary between studies, the overall trend shows darker colours like black absorb the most solar energy and light shades like white reflect the most heat.
Best and Worst Colours for Heat Reflection
Based on both physical properties of light and colour along with scientific measurements, here are the colours that reflect the most to least heat from sunlight:
Best Heat Reflecting Colours
- White
- Silver or polished chrome
- Yellow
- Green
Worst Heat Reflecting Colours
- Black
- Red
- Blue
- Purple
White, silver, and light yellows reflect the most sunlight and absorb the least heat. Dark shades of red, blue, purple, and especially black get the hottest in sun exposure. Choosing light colour paints, fabrics, or coatings can help reflect solar heat in hot conditions.
Using High Heat Reflectance Colours
Taking colour heat reflectance into account allows choosing materials and finishes that can keep buildings, vehicles, clothing and more cooler in sunny conditions:
- Paint house exteriors white or light yellow rather than dark red or brown
- Choose light chrome metal over black plastic for vehicle trim
- Select white or light-coloured roofing shingles instead of black
- Wear light-coloured lightweight shirts and pants instead of black during summer
- Use white or aluminum foil sunshades on vehicle windshields
High solar reflectance materials can also reduce air conditioning costs in buildings. One study estimated painting a roof white instead of black could lower summertime air conditioning demand by over 20%.5
Conclusion
White and light colours like yellow, green and silver reflect the most solar heat, keeping surfaces cooler than darker colours. Black absorbs up to 90% of sunlight as heat, making it the hottest colour in sun exposure. Understanding colour heat reflectance allows smarter choices of building materials, car colours, clothing and more to stay cooler on hot sunny days.
