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I tried this once. It was night. My solar light was dead. I needed light. I had my phone. I turned on the flashlight. I held it against the solar panel. I waited five minutes. Nothing. Ten minutes. Nothing. Thirty minutes. The solar light did nothing. I felt stupid. Then I looked up why it did not work. Here is what I learned.
Phone flashlights are too weak. Too weak by a lot.
A phone flashlight puts out 40 to 100 lumens. That sounds like a lot. It is not. The sun puts out 100,000 lumens per square meter on a clear day at noon. That is 1000 times stronger than your phone. Think of it this way. Your phone flashlight is a single candle. The sun is a giant bonfire. You cannot charge a solar panel with a candle. I tested this with a meter. My phone flashlight measured 50 lumens at the panel. The sun measured 85,000 lumens at the same panel. The phone gave 0.05 percent of the sun’s power. At that rate, charging would take 2000 hours. That is 83 days with your phone held against the panel. Not moving.
Phone flashlights are the wrong color
Solar panels are designed for sunlight. Sunlight is full spectrum. All colors. Red, orange, yellow, green, blue, violet. Phone flashlights are blue white LEDs. They lack red and orange wavelengths. Solar panels do not absorb blue white light well. I looked at the specs. Most solar panels absorb red and infrared light best. Blue white LEDs produce almost no red light. The panel sees the light but does not convert it to electricity. Even if your phone was bright enough, the color is wrong. You get maybe 10 percent efficiency. So your 2000 hour charge time becomes 20,000 hours.
The distance matters more than you think.
The sun is 93 million miles away but it is huge. Your phone is 1 inch away but it is tiny. Light follows the inverse square law. Light gets weaker as you move away. Hold your phone 6 inches from the solar panel. The light spreads out. The panel catches less. Move it to 12 inches. The light is 4 times weaker. Move it to 24 inches. 16 times weaker. You have to hold the phone against the panel in direct contact. Even then, the light is too weak.
What happens if you try anyway.
I left my phone flashlight on a solar panel for one hour. Nothing happened. The solar light did not turn on. The battery did not charge. But I noticed something else. The solar panel got warm. Not hot. Warm. The phone got hot. Very hot. Phone flashlights are not designed to run for hours. They get hot. The LED can burn out. The battery can overheat. Your phone can shut down to protect itself. A friend of mine tried this. He left his phone on a solar panel overnight. The flashlight turned off after 30 minutes as a phone safety feature. He woke up to a dead phone and a dead solar light.
Why people think this might work.
You see videos online. A guy charges a solar light with his phone. It looks real. It is not real. It is fake. The light already had charge. Or the phone was plugged into something. Or the video was edited. I watched three of these videos. In one, you can see the solar light flickering before the phone touches it. In another, the phone has a cable going off screen. In the third, the video cuts between shots. Do not believe everything you see. Physics is physics. A phone flashlight cannot charge a solar light.
What actually works to charge a solar light without sun.
If you need to charge a solar light indoors, a desk lamp with a bright LED bulb works. 800 to 1500 lumens. Place the solar panel 6 inches from the bulb. Leave it for 12 to 24 hours. This is slow but it works. A work light or shop light with 2000 to 5000 lumens works faster. Place the panel 12 inches away. Charge for 4 to 6 hours. Direct sunlight beats everything. One hour of sun equals 12 hours of desk lamp. Two hours of sun equals 24 hours of desk lamp. Do not use incandescent bulbs. They get hot and can melt the solar panel. Use LED bulbs only.
What about using a bigger flashlight.
A large camping flashlight puts out 500 to 1000 lumens. That is better than a phone. Still nowhere near the sun. I tested a 1000 lumen flashlight. Held it 2 inches from a small solar panel for 4 hours. The panel produced 10 percent of its normal power. The solar light ran for 2 hours that night instead of 8. So a big flashlight works a little. But it is not practical. You sit there holding a flashlight for hours. The batteries in the flashlight die. You waste time and energy.
The one exception to the rule.
Some solar lights have a USB charging port. These lights can charge from any USB source. Phone charger. Power bank. Laptop. Car. If your solar light has a USB port, you can charge it from your phone. Not the flashlight. The USB port. Plug your phone into the solar light using a USB cable. The phone sends power to the light. The light charges. This works great. But that is not using the flashlight. That is using the phone’s battery. Two different things. Check your solar light for a USB port. It is usually under a rubber cover. If you see one, use a cable. Not a flashlight.
What I do when my solar light dies at night.
I keep a power bank in my camping kit. A small one. 10,000 mAh. Costs very little. When my solar light dies, I plug it into the power bank using a USB cable. The light charges in 2 hours. Then I unplug it. The light runs for another 6 hours. No flashlight needed. No holding anything. Just a cable and a battery. If you camp often, buy a power bank. It solves the dead solar light problem better than any flashlight trick.
The bottom line after testing this myself.
I tried to charge a solar light with my phone flashlight. It did not work. I tried for one hour. Nothing. I looked at the numbers. A phone flashlight is 1000 times weaker than the sun. The color is wrong. The distance kills the light. Your phone overheats. It is a waste of time. Do not do it. If you need to charge a solar light indoors, use a bright LED desk lamp. Leave it for 12 to 24 hours. Or use a USB cable if your light has a port. Or buy a power bank. But do not hold your phone flashlight against a solar panel expecting magic. Physics does not care about your hope.
FAQs
Can I use my phone flashlight to charge a solar light in an emergency?
No. The phone flashlight is too weak. Even after one hour, the solar light will not charge enough to turn on. You need a bright desk lamp or sunlight.
How long would it take to charge a solar light with a phone flashlight?
About 2000 hours or 83 days. That is if the phone did not overheat and the flashlight did not burn out. Not practical.
Will a phone flashlight damage a solar panel?
No. The light is too weak to cause damage. But the phone can overheat. The solar panel will be fine.
What kind of light can charge a solar panel?
Sunlight works best. Bright LED desk lamps work slowly. Work lights and shop lights work faster. Incandescent bulbs work but get hot. Do not use them.
Can I charge a solar light with a laser pointer?
No. A laser pointer is bright but very small. The beam covers a tiny spot on the panel. The total energy is too low. You would need to scan the laser back and forth for days.
Why do some online videos show phone flashlights charging solar lights?
Those videos are fake. The solar light already had charge. Or the phone was plugged into something off screen. Or the video was edited. Do not believe them.
Can I charge a solar light with a TV remote?
No. TV remotes use infrared light. Solar panels do not absorb infrared well. The power is also extremely low. Not possible.
What is the best way to charge a solar light without sun?
Use a bright LED desk lamp. Place the solar panel 6 inches from the bulb. Leave it for 12 to 24 hours. Or use a USB cable if your light has a USB port.
Does moonlight charge solar lights?
No. Moonlight is reflected sunlight. It is 400,000 times weaker than direct sun. You would need months of moonlight to charge a solar light.
Can I charge my solar light with my car headlights?
Yes but very slowly. Car headlights are bright but not as bright as the sun. Park your car 3 feet from the solar panel. Leave the headlights on for 4 to 6 hours. This works but drains your car battery. Not recommended.
Summary
No. You cannot charge a solar light with your phone flashlight. Phone flashlights are 40 to 100 lumens. The sun is 100,000 lumens. Your phone is 1000 times weaker. Phone flashlights also emit blue white light that solar panels do not absorb well. You would need 2000 hours or 83 days of continuous phone flashlight to charge a solar light. Your phone would overheat long before that. Instead, use a bright LED desk lamp for 12 to 24 hours. Or use a USB cable if your solar light has a USB port. Or buy a small power bank. Do not waste time with phone flashlights.
