Written records about the idea of seasonal fluctuations in well-being have existed since 400 bc. Research has shown that light therapy is beneficial in patients with seasonal affective disorder ^{Reference Eagles1} but most clinicians have little experience of using it as a treatment in their clinical practice. This practical book will help clinicians to understand both seasonal affective disorder and light therapy. It is well organised, each chapter beginning with a list of topics covered, and with tables, clinical examples and tips to facilitate a better understanding of the main concepts.

As it can be challenging to diagnose seasonal affective disorder, the authors begin with its definition and criteria to differentiate it from major depressive episode and other related conditions. The mechanism of light therapy is well explained and the advantages and disadvantages of various types of light devices are discussed. The book covers different conditions that light therapy can be used for as well as rare side-effects. It ends with information on rating scales that might be useful in patients with seasonal affective disorder, and online resources for further information.

Although it is difficult to obtain randomised control studies on a treatment such as light therapy, the authors mention meta-analyses that have shown that morning light therapy is a well-validated, evidence-based treatment for seasonal affective disorder. What I found interesting is that response to light therapy can be very rapid, with an immediate energising effect of bright light and improvement in depressive symptoms starting within a week. Light therapy could be a good treatment option in specific population groups, such as in pregnant women with depression, for whom a non-pharmacological treatment might be preferable.

Overall, this is a useful book for those who would like to better understand the practical applications of light therapy.