Black has an LRV approaching 0% as it absorbs almost all light. In contrast, white has 100%. All other colours fall between these two numbers. The sheen level of the coating can also have an effect (Dulux LRVs are based on a low sheen finish).

Any light absorbed by a coating is converted to heat, so a colour with a low LRV will get hotter than a colour with a high LRV.

Some substrates are heat sensitive, and their suppliers have elected to specify restrictions on the tone of colours (LRV) that can be applied. This may restrict colour selection to LRVs of greater than 40% — which is really only a colour of mid-shade darkness.

A white undercoat can help greatly in reducing the heat build up in a substrate. As a rule, it's best to follow the supplier's LRV recommendations to avoid substrate movement, which can lead to warping, cracking and potentially leaking.