Some plants produce sun leaves in direct sun and shade leaves where the leaves are shaded by others. Sun leaves become thicker than shade leaves because they develop longer palisade cells or an additional layer of palisade cells.

Lindleys plant is sun burnt because lack of sun control. When you look at it you can see the plants leaves outline on other leaves. A way to prevent this is to hardening off the plant. This is when you slowly introduce the plant to the sun. For example you can put it out for 30 minutes one day, 40 the next and so on.