kerosene expenditure contributed to a decline in the total expenditure of treated households by 2 to 6% (reported in columns (q) and (r), respectively). This decrease in annual expenditure corresponds to approximately 21―63 USD. The products cost 39.6, 13.6, and 9.7 USD (based on the exchange rate at the end of October 2016) for S250, S10, and S2, respectively. Given product durability (at least five years with normal use) and the potential health benefits resulting from indoor air-quality improvement, solar lamps appear to be cost-effective and to increase household savings. These findings make us reasonably confident that treated households genuinely used the solar products.<sup>14</sup>

# **Educational inputs**

Given the rejection of the first possibility that might explain no positive treatment effects on educational achievement, this subsection checks the second possibility by investigating the impacts of solar products on students’ educational inputs in Table 5 and Table 6.

In Table 5, we first estimated the impact of solar products on students’ use of time, with or without baseline controls. Data on the daily time-use activities of our sample students were periodically collected from September 2013, using time diaries that our research team had asked each household to use to record their daily time-use activities. Using information drawn from these diaries increased the reliability of our analysis. However, a significant amount of time-use information was unavailable after April 2014, because of several happenings, including a change in the diary format and the training of those carrying out the survey (May and June), a school holiday for Ramadan (July), and floods that caused the temporary evacuation of (some) respondents to shelters (August). This natural disaster also made it difficult for teachers to ensure that students regularly filled out their time diaries, once school resumed in September. For these reasons, we could only use the time diary information gathered between September 2013 and April 2014; the relevant estimation results during this period are detailed in Table 5.

As the results in Table 5 show, our estimates reveal that, on average during the eight-month period, treated students significantly reallocated the amount of time used for home study, reducing daytime study by approximately 5―8 minutes each day, and increasing nighttime study by 20―25 minutes. The net effect of solar lanterns on study time at home was found to be statistically significant and positive. This net effect can be translated into an increase of 45―75 hours of home study time over eight months. In addition, comparing the treatment effects in columns (e) and (k) in Table 5 with the control mean reported at the bottom of these columns and columns (d) and (j), treated

> 14In Table S.12 in the supplemental appendix, we also attempted to assess treatment effects on a household’s willingness to buy solar products. The dependent variable takes one if the respondent is willing to buy each type of solar lantern. This variable measures subjective satisfaction; the corresponding information was collected during a follow-up survey. As the results in columns (a) and (e) show, treated households became more willing to buy solar lamps than those in the control group. We also estimated the willingness of both treatment and control group households, which showed an interest in purchasing solar products, to buy particular products in columns (b)―(d) and (f)―(i). Interestingly, treated households were mainly willing to purchase products they had used during the experiment. In other words, households that had received only one product (S250) generally wanted to purchase S250, whereas three-product users were willing to buy all three products. The increased satisfaction revealed by these exercises also confirms that the treated households genuinely used the solar products.

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