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ExpaLight

ExpaLight is a red LED flashlight powered by a supercapacitor, designed especially for astronomical observations. The project originated for use during observation nights at summer astronomical schools at the observatory. Thanks to its robust and open-source design, ExpaLight is suitable for both amateur and professional users.

Technical Parameters

Parameter	Value
Stored energy	350 J
Light duration	~10 h
Charging time	< 50 s (typ.), max. 2 min
Charging indication	Green LED off at 80% voltage
Charging interface	MicroUSB, ≤500 mA
Housing	3D-printed PLA, durable, water-resistant
Light Source	High-efficiency red LED

Key Features

• Supercapacitor energy storage (350 J)
• Light duration: up to 10 hours
• Fast charging: typically under 50 seconds, max. 2 minutes from full discharge
• Charging indication: green LED turns off at ~80% voltage
• Durable 3D-printed housing, mechanically and water resistant
• High-efficiency red LED, optimized for dark adaptation of the human eye
• No batteries needed, USB charging (microUSB)
• Open-source and repairable

ExpaLight remains an active project despite repository inactivity. The design was made to withstand years of usage.

Product manual – Czech version

Why red light?

Astronomers use red light because it preserves the dark adaptation of the human eye, making it ideal for observing the night sky.

Usage

• Can be placed horizontally (ideal for writing into observation logs)
• Can stand vertically with LED up or down
• Can be recharged while in use
• Works even when permanently connected to a charger

Maintenance

• Clean with cloth and mild soapy water
• Do not wash under running water or immerse in liquids
• Avoid abrasive tools to prevent scratching the housing

Frequently Asked Questions

Do I need to switch it off? No. The flashlight has no mechanical switch. It shines until fully discharged, then you recharge it via USB.

Why this shape? The hexagonal body prevents rolling, ensures stable positioning on surfaces, and supports versatile use (e.g. headlamp attachment in future).

Can I leave it charging permanently? Yes. The electronics are designed to handle permanent connection safely.

What happens if it is fully discharged? Nothing. Unlike battery-based lamps, the supercapacitor can be fully discharged without degradation.

Can I use a mobile charger? Yes. Any standard microUSB charger (5V, ≤500 mA) or USB port will work. Some smart chargers may fail due to low current draw — in that case, use another charger.

Availability

You can purchase ExpaLight at Tindie or contact us directly at [email protected].

Contributions

ExpaLight is an open-source hardware project. Suggestions and improvements are welcome! Please open an issue in the GitHub tracker.