It’s common knowledge that dark colors get hotter than light ones in the sun. But new research from Lawrence Berkeley National Laboratory reveals an exception. Some dark pig- ments stay just as cool as white thanks to fluorescence, which occurs when fluorescent materials immediately re-emit
Led by scientist Paul Berdahl, the research team focused on ruby
red coatings created from a mix of aluminum oxide and chromium.
They first discovered that white paint covered with a layer of synthetic ruby crystals remained cooler than an off-white surface.
The scientists then created several shades of ruby pigment to
mix into coatings, which were applied over white substrates. The
ruby paint samples stayed just as cool as white materials, though
Berdahl notes that creating ruby powder that was as deeply colored as the crystals was significantly more labor-intensive. In both
applications, fluorescent cooling boosts the pigments’ performance
by re-emitting some of the visible light that the surface absorbs to
appear dark rather than passively reflecting it.
Berdahl also identifies blue materials that fluoresce and can be
combined with other colors to yield green and black materials that
remain cool. Prototype fluorescent coatings are currently undergoing weathering tests, and the commercialization of the pigments is
not expected to be costly, Berdahl says.
“Rubies have a reputation for being expensive, but they’re
mostly aluminum oxide, which sells for about 30 cents per pound,”
The full results were published in the journal Solar Energy
Materials & Solar Cells.
How These ‘Better Buildings’
DEPARTMENT OF ENERGY PROGRAM HAS
SAVED $3 BILLION IN ENERGY COSTS
Can Dark Roofs Stay as
Cool as White?
RUBY RED ROOFING MATERIALS KEEP UP
WITH COMMERCIAL COOL ROOFS
Each year, American industries spend roughly $200 billion on energy costs. Looking to cut back, companies and insti- tutions are teaming up to innovate and are finding strong results in improving energy practices. A dozen partners in the DOE’s Better Buildings, Better Plants program have hit
their goals for energy or water savings and are cutting out much of
their energy expenditure.
Better Buildings, Better Plants
was launched five years ago to make
commercial, public, industrial and
residential buildings 20% more energy
efficient over 10 years from when
partners join the program. Together,
Partners in the program represent more than 11% of the manufacturing
sector’s total energy footprint with over 2,500 facilities across the U.S.
and have so far reported cumulative energy savings of 600 trillion
BTUs and nearly 35 million metric tons of avoided climate-changing
“This hugely successful program involves thousands of facilities,
avoiding millions of metric tons of carbon emissions and saving billions
of dollars in energy costs,” says Energy Secretary Ernest Moniz. “The
progress that our Better Plants partners have made throughout the
Obama Administration indicates that American companies are com-
mitted to reducing the energy footprint of their operations. That com-
mitment is essential for America to continue making important strides
How have these partners cut back on energy? Facing the split
incentive barrier that came with a portfolio of 150 leased distribution
spaces, Lennox International feared that they would not be able to
make progress in energy efficiency. With Lennox having little incentive
to invest major capital into building upgrades and the building owners
having little desire to upgrade because they did not pay energy bills,
Lennox chose to work with a lighting technology provider to set light-
ing specifications for its leased facilities and negotiated with its land-
lords to split lighting upgrade costs.
In an attempt to conserve water, HARBEC Plastics innovated a rainwater system to fulfill an insurance requirement to implement a fire
sprinkler. Instead of installing a water tank, HARBEC created a water
retention pond that collects rainwater from roofs and parking lots to
supply the sprinkler. Moreover, HARBEC uses the pond to meet cooling
needs for the facility’s evaporative cooling towers.
Learn more by visiting the Better Buildings Solution Center at