activities, durable and nondurable assets, and debts and savings.

# **Experiment and survey**

Once we had completed the baseline household survey, we organized a public lottery to randomly allocate to the eligible students access to the use of solar lights in two different bundles of products for 16 months (September 2013 to December 2014). The first treatment bundle (Treatment A) contained all the d.light solar products, i.e., the S250 (solar lantern with mobile recharging), the S10 (general solar lantern with no cellular recharging facility), and the S2 (simple solar lantern), altogether providing approximately 164 lumens of lighting capacity at top brightness settings. The second treatment bundle (Treatment B) contained only the S250 solar lantern, providing lighting capacity of 110 lumens at the maximum brightness setting. By differentiating the treatment intensity, we are able to explore whether the provision of smaller lanterns had any additional impacts, such as facilitating and ensuring intended use of the main product by the targeted children. For example, other members of the treated households may have wanted the solar lanterns for their own use (for example, to facilitate cooking), which may have reduced the impact of the solar lanterns on the targeted students. Hence, bundling additional solar products may have reduced the probability of such alternative unintended usage by other household members and siblings.

We held public lotteries, at each sample school, in the presence of parents, teachers, and village elites. Students and their parents drew a lottery by themselves and were classified into one of the following three groups accordingly: (1) Treatment A, (2) Treatment B, and (3) the control group that did not receive any solar lantern. The randomization was separately implemented at each school for each grade, so that the ratio of Treatment A, Treatment B, and the control groups was maintained at approximately 5:4:9 for each grade at each school. By allowing each household to join the lottery only once, we avoided the possibility that siblings from the same household would be simultaneously in the treatment and control groups. After the public lottery, there were 248 students in Treatment A, 198 students in Treatment B, and 436 students in the control group (see also Table S.1 in the supplemental appendix). In our experiment, no treated students refused to use the offered solar products.

To effectively recharge the solar products, obstructions to sunlight (e.g., walls, trees) needed to be avoided. Furthermore, the tilt angle of the panel was also important for adequately recharging the lanterns under sunlight. To facilitate proper maintenance and the correct recharging practice, a product manager of a local selling agency was invited to the study site to train our enumerators, who in turn instructed the survey respondents and their children. Moreover, to ensure that these sets of instructions were readily available to our sample households, we provided each of them with a detailed pictorial manual. This manual contained elaborate information on the adequate use/maintenance and recharge techniques of the solar lanterns. It also included a detailed time diary for maintaining hourly records of 8