each student’s time use for various activities (e.g., hours of playtime outside of school, study time at home, etc.) (see Figure S.3 in the supplemental appendix for a sample of the collected time diary). Teachers were held responsible for regularly checking these time diaries, which were periodically collected by our survey team. Furthermore, to facilitate accurate time keeping, we gave both the treatment and control students a wall clock and set of batteries.

After the implementation of the randomized control trial, we periodically visited the schools to collect the monthly time-use diaries. Moreover, one year after the baseline survey, we implemented a follow-up study of the same children and their households to construct a picture of any welfare and behavioral changes that had taken place over one year. During the follow-up phase, we could trace 852 of these households (i.e., 96% of the 882 original sample households), thus with the minimal rate of sample attrition; the rest had been lost due to attrition for reasons such as relocation or marriage. Furthermore, we collected the detailed annual examination scores of each student from our sample schools for both the 2013 and 2014 academic years.

To comply with ethical concerns, access to solar lights was provided for 16 months and was subject to withdrawal and re-distribution to our control households following the research. To ensure that this process went smoothly, we issued legal documentation to each treated household, describing the conditions for access to the solar lights, including information on proper use, product responsibility, prohibitive practices (e.g., renting or sub-leasing), and withdrawal requirements.<sup>4</sup> In this contract, we made the households responsible for product loss (e.g., theft), which might have encouraged no such cases occurring in our experiment in the end. However, in the case of product malfunctioning (e.g., defects), we replaced the product on verification of the malfunction by the sales unit. We believe that this process reduced the possibility of contaminated data from the product’s unintended use.

Note that the way a new technology is obtained (whether through free distribution or purchased from a market) may affect its use and resulting socio-economic impacts (Ashraf et al., 2010; Cohen and Dupas, 2010). Therefore, the findings of the current research project are limited by its experimental design and should be viewed with caution when considering the influence of provided solar lamps in general.<sup>56</sup>

> 4Relatedly, we began this research by approaching school headmasters and School Management Committees to explain the project details and obtain their verbal approval. Next, we visited households to confirm their eligibility and explain the survey and study design; before starting our baseline survey, we obtained their written (signed) consent. We went through the same steps to obtain the participants’ consent before conducting a follow-up survey. Information on the students’ academic performance was collected directly from the schools, once all of the parents and School Management Committees had approved this form of data collection. Our survey questionnaire adopted the standard income and expenditure modules used in the Bangladesh Bureau of Statistics (BBS) Household Income and Expenditure Survey.

> 5In this study, the solar lanterns were given for free to use for 16 months (cost-free leasing); people who pay to lease such lanterns may be influenced by the sunk cost effect to use them more intensively. However, Ashraf et al. (2010) and Cohen and Dupas (2010) provided no evidence to support such effects in the context of health-related products. In addition, charging non-zero prices for solar lamps or any other items may encourage those most committed to using the products to purchase them, while reducing the wastage that results from unused products. While the available evidence is mixed (e.g., Ashraf et al., 2010; Cohen and Dupas, 2010), Ashraf et al. (2010) makes the point that large up-front costs and the product’s ability to be extensively used for secondary purposes may facilitate such screening effects. While the market price of solar products may not be particularly high for most households, ultra-poor households may not be able to afford them. Given that solar lanterns can also function as cellular phone chargers, this modern technology might have been more intensively used (due to screening effects) if we had leased the lanterns at non-zero prices.

> 6A one-time free distribution of solar products may also affect users’ subsequent purchasing/adoption behavior by altering their reference points (i.e., anchoring effects) and/or the perceived product benefits (i.e., learning effects) (e.g., Dupas, 2014). Relatedly, a limited time lease may also encourage users to treat the technology carefully.

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