Although light therapy is effective in the treatment of seasonal affective disorder (SAD) 
, or Major Depressive Disorder with a Seasonal Pattern, as well as for non-seasonal depression 
, data suggest that only about 41% (24 out of 59) of SAD patients treated successfully with light therapy (LT) report regularly using the treatment in follow-up studies 
. In another study combining LT and cognitive behavioral therapy (CBT), only 12% (4 out of 34) of individuals with SAD originally treated with LT alone (n
19) or LT plus CBT (n
15) used LT during the following winter 
. These data suggest that the choice to use light therapy is itself a target for intervention. In the present study, we aimed to test whether certain motivational and social cognitive processes may help explain the decision to utilize LT.
Two separate issues exist, 1) LT use during the acute treatment phase, and 2) LT use in subsequent winters. However, similar factors may be associated with LT use in both instances. Among those using LT, only 53% of all those with SAD and 43% of moderate to severe cases meet remission criteria after LT 
. A more recent light therapy trial found higher remission rates, ranging from 46% to 79%, depending on the stringency of remission criteria 
. These remission rates compare favorably to remission rates for antidepressant medications, which ranged from 43% to 62% in recent meta-analyses and pooled analyses 
. Maximizing remission rates may require higher rates of adherence to LT prescriptions. Adherence to LT in SAD is lower than hoped, about 41%–60% 
when treatment dropouts are included, and this incomplete adherence may explain the incomplete remission rates. The general literature on medication and medical treatment compliance suggests dose-taking compliance declines as the number of daily doses increases 
, and depression symptoms are associated with noncompliance 
. Light therapy requires approximately 30–45 minutes a day, which represents a significant time commitment. Factors associated with light therapy use and adherence could be clinically relevant if such factors could be manipulated to help improve treatment outcomes.
In the one study to date assessing possible explanations for not using light therapy, 59 patients originally treated with light therapy were reassessed approximately 9 years later 
. Among the 56% (n
33 out of 59) who had discontinued using light therapy, 14% (n
8) reported they had not had sufficient symptoms, leaving 44% of individuals who did have sufficient symptoms to warrant treatment but chose not to use light therapy. Those individuals reported inconvenience and/or perceived ineffectiveness as reasons for not using light therapy despite having experienced improvement during initial light therapy treatment. To examine further which factors predict light therapy use, we reviewed research on treatment adherence in depression and other similar health conditions in which treatment requires a time commitment.
The Transtheoretical Model 
, and Social Cognitive Theory 
both describe variables that have been identified as important predictors of compliance with treatments such as continuous positive airway pressure (CPAP) treatment for obstructive sleep apnea, a treatment requiring nightly use of a CPAP mask and machine somewhat similar to the daily use required for light therapy 
. Factors such as self-efficacy and depression symptoms have also been associated with adherence to treatments for depression. The Theory of Planned Behavior hypothesizes that tangible barriers (e.g., access to care), illness barriers (e.g., depression symptoms, concerns about treatment), and psychological barriers (e.g., self-efficacy, stigma) are modifiable and, therefore, targets of interventions to improve adherence to medication treatment of depression 
. An intervention based on this model that incorporates motivational interviewing, problem solving, and psychoeducation has shown a significant increase in adherence to medications in older adults with depression from baseline across 24 weeks compared to treatment as usual 
Although different in their mechanisms of efficacy, homework within the context of psychotherapy has similar duration and daily frequency demands as light therapy. A recent meta-analysis of 23 studies on homework found that homework compliance had a small to medium effect (r
.26) on treatment outcome 
. Individuals with more severe or longer-lasting symptoms comply less with homework 
. Variables including motivation, readiness to change, and necessary skills are correlated with homework compliance and treatment outcome in cognitive behavioral therapy for depression 
The above data on factors associated with adherence to either homework in psychotherapy or medication treatment for depression utilize constructs from multiple theories of behavior change. Fishbein et al. (2001) 
proposed an integration of social cognition, health belief, and other models and focused on eight shared variables including intention to change behavior, environmental barriers, skills, outcome expectations or attitudes, norms, self-standards, emotion, and self-efficacy. The Fishbein et al. (2001) 
report focused on AIDS-related health behaviors that may have a similar burden of daily frequency and duration as light therapy. Neimeyer and colleagues (2008) 
recently reviewed theoretical models appropriate for predicting homework compliance in psychotherapy and found that willingness, as well as motivation and stage of change predicted homework compliance.
Aims of the Study
We hypothesize that the aforementioned variables such as social support, self-efficacy, and treatment credibility will predict use of LT in individuals with SAD or non-seasonal depression. Therefore, the present study sought to collect preliminary data using an anonymous web survey of individuals self-identifying as having been previously diagnosed with a disorder for which light therapy is indicated as a treatment. Specifically, we hypothesize that the decision to use LT in the previous winter would be associated with cognitive, behavioral, and social variables including self-efficacy, outcome expectations, social support, processes of change, knowledge and the degree of perceived treatment credibility. We further hypothesized that LT non-use would be associated with higher frequency of self-reported depression symptoms in the previous winter.