Difference Between UV, IR and Visible Rays, and What Each Does to a Building

UV IR and visible radiation are three parts of sunlight that affect buildings in different ways. Ultraviolet (UV) breaks down materials, infrared (IR) delivers most of the heat, and visible light provides brightness and some heat. Panache Green designs heat-reflective coatings around this split.

The Solar Spectrum at a Glance

Sunlight reaching the ground is roughly 5% UV, 43% visible and 52% near-infrared. ASHRAE gives a slightly different split of about 3%, 47% and 50%, but the message is the same: more than half of solar energy arrives as infrared, which you cannot see.

What Does Ultraviolet Radiation Do?

Ultraviolet radiation in buildings causes damage rather than heat. It breaks polymer chains in paints, sealants and membranes, which shows up as chalking, cracking, yellowing and loss of flexibility.

Typical effects:

• Faded facades and interiors near glass
• Embrittled sealants and joints
• Chalky, flaking paint
• Shortened waterproofing life

UV stability is why roof coatings use specialised binders and protective topcoats. Panache Green’s Cool Tops Premium includes a transparent UV-resistant layer as part of its three-product system.

What Does Visible Light Do?

Visible light carries about 43% of solar energy. It lets you see colour and provides daylight, which can reduce lighting needs. UV IR and visible radiation It also heats surfaces that absorb it, which is why dark colours run hotter than light ones.

For roofs, visible reflectance explains why white and light surfaces look cooler. But it’s only part of the story, since a dark-looking surface can still reflect infrared strongly if cool pigments are used.

What Does Infrared Radiation Do?

Infrared heat radiation is the largest contributor to roof heating. Near-infrared makes up about half of incoming sunlight, and most building materials absorb it well. Once absorbed, it becomes sensible heat in the slab or sheet.

Infrared also plays a second role. Surfaces emit long-wave infrared when warm, which is how a cool roof sheds heat at night. That’s why thermal emittance matters alongside reflectance.

How These Rays Combine to Heat a Building

Solar radiation and building temperature are linked through three steps:

1. Radiation strikes the roof or wall.
2. The surface absorbs a share, depending on reflectance.
3. Absorbed energy conducts inward and raises indoor temperature.

On a dark RCC roof, surface temperatures reach 60 to 70°C in Indian summer. A reflective coating with an SRI of 109 can reduce that by around 18 to 20°C on concrete.

How Heat-Reflective Coatings Respond to Each Band

Heat-reflective coatings treat each band differently:

• UV: reflected or absorbed by stabilisers in the binder to protect the film.
• Visible: partly reflected, depending on colour.
• Infrared: strongly reflected by engineered pigments, the main cooling mechanism.

Panache Green’s coatings are formulated to reflect a large share of infrared, with reported solar reflectance of 0.87 and emissivity of 0.86 for Cool Tops Premium.

Why This Matters for Specification

Most product brochures talk about “heat reflection” without saying which band they mean. A coating can perform well in the visible range and poorly in the infrared, and the roof will still run hot. Panache Green asks for spectral reflectance data when a consultant wants to dig deeper, and we share the test method used. It’s a small question, but it separates marketing language from engineering evidence.

Practical Implications

• Do not choose roof coatings by colour alone.
• Ask for reflectance across the full spectrum, not just visible.
• Prioritise UV-resistant topcoats for long service life.
• Consider walls too: east and west facades receive intense, low-angle sun.

For west walls, Panache Green’s Cool Wrap reports SRI of 107 and a surface temperature reduction of 10 to 15°C.

A Simple Way to Picture It

Think of sunlight as a mixed delivery. UV is the abrasive part that wears materials down. Visible light is the part you notice. Infrared is the quiet heat load that nobody sees but every roof feels. Panache Green builds its coating systems to handle all three, which is why the stack includes a primer, a reflective layer and a protective top coat.

Common Misconceptions

• “Heat is the same as light.” In reality, much of the heat arrives as invisible infrared.
• “Dark colours always mean hot.” Cool pigments can break this rule.
• “UV causes heat.” UV mostly causes degradation, with only about 5% of the energy.

Understanding UV IR and visible radiation helps architects choose materials that last and keep spaces comfortable.

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