I'd like to make a solar panel that lights up an LED, not by charging a battery to power the LED, just live energy it is getting from the sun. I'm a real noob and need some advice. What panels should I pick, what specifications? I would like to make this work quite long but be easy to make. It's a normal single 2-3v (red,...,white) 5mm led that I'm thinking about

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    \$\begingroup\$ Check out the solar lights that exist, that will give you some circuit ideas. \$\endgroup\$ – Solar Mike Jan 1 at 14:11
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    \$\begingroup\$ I, however, slightly doubt the sensibility of this; when the sun is shining is exactly not the time when you need an LED to light up, usually. Also, you're really very much underdefining what you want to do: it makes kind of a difference whether you need a dim indicator LED to light up somewhere, or whether you want to illuminate a large room to a degree that would be workplace illumination. Start by writing down how much light you want, then try to figure out how much power the LEDs necessary to achieve that will need, then what amount and kind of solar panel you'll need for that. \$\endgroup\$ – Marcus Müller Jan 1 at 15:40
  • \$\begingroup\$ And be prepared to be disappointed about how much energy you get from the solar panels you can buy in DIY shops. (I was!) \$\endgroup\$ – Oldfart Jan 1 at 17:12
  • \$\begingroup\$ What LED specification - voklts, current, ... ? What application? || Panel - resistor - LED || R = V/I = (Vpanel - L_LED)/required_current.) Ppanel ~= 2 x PLED. \$\endgroup\$ – Russell McMahon Jan 1 at 20:36

Red LED's require only ~1.6-2.0 volts to light. The solar panels on "dollar store" solar-powered LED lights should produce about that voltage, at a few mA current. Just connect the two wires from the panel to the LED, observing polarity.

The current from the solar panel is so low that no dropping resistor is needed. Use a long wire, so the panel can be in the sun, and the LED in a dimly-lit room, since the LED will not be too bright.

If you know a prisoner in a deep dungeon, or a troglodyte such as Gollum, this would be useful to let her or him know when to count another day of confinement.

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    \$\begingroup\$ the sense of humour at the end.. I loved it. \$\endgroup\$ – muyustan Jan 2 at 0:32
  • \$\begingroup\$ Could I know the specs? I live in eastern Europe, so I'm probably going to buy the panels off the internet. \$\endgroup\$ – realnoob Jan 2 at 9:38
  • \$\begingroup\$ @realnoob I would guesstimate these specs: Voltage 3-4V or more (I think 6V is common), current 20 mA or more. And that's probably more than it really needs. As DrMoishe said, you do not need a very big solar panel! It should be quite small, and therefore cheap. \$\endgroup\$ – user253751 Jan 2 at 17:02
  • \$\begingroup\$ Could it be 120 mA? Is that too much? \$\endgroup\$ – realnoob Jan 2 at 17:07
  • \$\begingroup\$ If it's more than ~30 mA, you need to cover part of the cell in bright sun to prevent damage to the LED. Or just use it indoors, e.g. to see if the light inside the refrigerator really goes off when the door is closed. \$\endgroup\$ – DrMoishe Pippik Jan 2 at 17:18

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