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Light Reflectance Values (LRV) Colours and Heat Generation

The LRV of a colour is an indication of what the temperature of the paint surface and substrate should reach in direct sunlight.

Black, the most absorbing of visible light and the thermal infrared, has a LRV very close to 0.

White is the most reflective of visible light. It also reflects a lot of the invisible thermal infrared, and has a LRV of approx 100.

You can therefore understand that dark colours do get very hot; lighter colours obviously the opposite.

We know that colours in the mid range of LRV 50 can absorb enough light and thermal IR to be (ambient conditions 22c) around 50/60c, which is hot enough for many substrates including wood.

We also know that as clouds pass over, temperatures on the surface can change rapidly. This rapid change in temperature does cause the paint film and the substrate to suffer stresses which can be reduced by a more reflective colour.

There are new pigment technologies around for paint colours that are more reflective of the visible and less absorbing of the invisible thermal infrared. Be careful when using these colours because the difference between a standard colour and the new pigment technology for heat generated can be very little.

As a guide, use colours on timber for exterior direct contact with the sun at LRV >50

Recommended links for LRV Colours and Heat Generation