Solar study lamp for a camp: cost, safety and repairability
An NGO orders 2,000 solar study lamps for a temporary school in a camp. The target retail price is $8, the lamp must last three years, and it must be safe for children aged 8–12. The current design uses three AAA NiMH cells, a 0.5 W LED, a 1 W PV panel, a push switch, and a two-part ABS body. After six months, field returns show: 18% switch failure, 12% battery over-discharge, 9% LED flicker, 7% body cracks after a 1 m drop, and 4% corroded USB sockets. Children often share lamps and leave them on the floor. The NGO wants a revised design that is repairable, uses no lithium, and can be built by a local assembler. The buyer is pressing for a lower price, and the supplier suggests removing the USB socket and using a cheaper switch.
1. Rank the failures using severity and frequency. Explain which two you would address first and why.
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Use risk = frequency × severity. Switch failure is highest at 18%; it can leave the lamp unusable and, if the switch short-circuits, may overheat. Battery over-discharge is 12%; it shortens life and may prevent recharging, directly defeating the three-year requirement. LED flicker at 9% is annoying and may cause eye strain. Body cracks at 7% are a safety issue because of sharp edges or small parts, but they are less frequent. USB corrosion at 4% is lower frequency but can block charging.
Address the switch and battery first because together they account for 30% of returns and both defeat the basic function and the three-year life. Body cracks should be next because of child safety. Do not treat the USB socket as a simple cost item: if it is the only charging route, removing it may make the lamp unusable with available chargers.
2. Propose design changes for the two priority failures and explain how you would evaluate them against the $8 cost target and three-year life.
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For the switch, replace the push switch with a sealed rotary or membrane switch rated for 100,000 cycles and at least IP54, and add strain relief so the wires are not pulled. For the battery, use three AA NiMH cells with a low-voltage cut-off at about 3.0 V and a resettable fuse, or a small charge controller that prevents over-discharge. Keep the cells replaceable through a coin-opened door rather than sealed in.
Evaluate with a cost breakdown: the switch may add $0.20 and the controller $0.35, so savings must come from simplifying the body or packaging, not from safety. Tests should include 100,000 switch cycles, 500 charge/discharge cycles to 80% capacity, ten 1 m drops, and a six-month field trial with 50 lamps. Acceptance: less than 2% failure and at least four hours of light after three years. This connects the design change to both the price constraint and the life requirement.
3. Discuss the ethical issue in the supplier’s suggestion to remove the USB socket and fit a cheaper switch. Refer to product evaluation and planned obsolescence.
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Removing the USB socket and fitting a cheaper switch shifts cost from the manufacturer to the user and the environment. If the switch fails, the lamp becomes waste; if the socket is the only charging route, removing it may make the lamp unusable with the chargers people already have. That is a form of planned obsolescence and conflicts with the three-year life and repairability requirements.
Ethical evaluation should consider duty of care to children, honest claims, life-cycle cost and e-waste. A better response is to keep a protected charging input, design for repair, publish a spare-parts list, and test the cheaper switch to destruction before accepting it. If the $8 target cannot be met safely, the NGO should renegotiate the specification rather than silently degrade the product. Product evaluation must include who bears the risk, not only the unit cost.