A reader asks:

 I notice that the CET Store is now offering a 7500 lux light box for the general public as well as a professional model with the standard 10,000 lux. Is 7500 lux really enough? Will it significantly increase the length of time I need to sit in front of it? Is the research leaning towards the conclusion that 10,000 lux might be overkill?

Answer:

7,500 lux is definitely within the active therapeutic range. Two recent studies using CET’s new unit were not with SAD patients, however. In those studies, patients with non-seasonal chronic depression or antepartum depression (depression during pregnancy) used the unit for 45 minutes to one hour. In a new study, patients with non-seasonal bipolar disorder are using the unit for 30 minutes or less. We do not yet know the general timing requirements, which will surely vary widely among individuals. It stands to reason that, on average, 7,500 lux-users will need somewhat longer exposure. 10,000 lux is not overkill, unless it is used in longer sessions than are necessary.