The ability to store the Sun’s energy for use at night is something our ancestors must have dreamed about. Fortunately for us, this dream is not only real, but it’s become the norm for humans everywhere. Solar panels have revolutionized light technology and have quite literally brought us out of darkness.
Solar lights are a simple solution for most homeowners. It’s easy to pop them in a place with plenty of sun and wait until the battery is fully charged. However, depending on your geographical location, the season, or the weather, sunlight levels may vary. In this case, you may need to be a bit resourceful when charging your lights.
In this article, we’ll explore how to charge your solar lights without sunlight so that you can get more use out of them. There are three main ways to approach the problem: using electricity, artificial light or indirect sunlight.
On This Page:
- How do Solar Lights work?
- The Basics of Solar Cells
- Charging your Solar Lights in Cloudy Weather
- 3 Ways to Make Sure you are Getting as Much Charge as Possible
- Can you charge a solar light with a flashlight?
- Can You Charge A Solar Panel With A UV Light?
How do Solar Lights work?
Before we dive into how to charge solar lights without the Sun, it’s important to first discuss how they work. Essentially, a solar light consists of a photovoltaic cell, a battery and a light all fixed together. There are several steps involved in the process of harvesting energy, converting it and then emitting it for use in a garden, emergency situation or pathway.
- Step 1: Light enters the photovoltaic cell and energy is collected in by the wiring of the mini solar panel. This electricity is then fed to the solar light’s battery.
- Step 2: The battery stores this energy as chemical energy during the daytime. The battery will then begin to provide it to the light when the battery is no longer being directly charged by the Sun.
- Step 3: The system lights up the LED bulbs which draw energy from the battery until it’s exhausted or daylight hours resume. LED is an obvious choice for solar lights due to their ultra-low energy usage.
The Basics of Solar Cells
The photovoltaic cells and amorphous cells used in solar panels can turn solar radiation into electricity. These cells are only able to effectively convert specific types of visible light into electrical energy. For example, infrared and ultraviolet (UV) light don’t contribute much to power production.
The most efficient form of visible light for power production is within the spectrum of violet to red, or the wavelengths of 380nm (violet) to 750nm (Red). You can either harvest this light naturally (using the Sun), or artificially (using other electric lights).
1. ELECTRICITY
This option is often the easiest as many solar lights come equipped with a power plug or USB connector. You can simply plug the light into the wall or an external power source and charge the battery, completely circumventing the solar panels altogether. In this way, the solar light functions just the same as a normal wired or battery-powered lamp.
Camping solar lights also often feature a DC car charger adapter. If you’re out in nature and don’t have access to a mainframe electrical system, this can be a real-life saver. However, if you’re planning on using solar lights while hiking or camping, always charge them beforehand. All it takes is one longer-than-expected hike or placing the light in a shaded spot to drain your battery.
2. ARTIFICIAL LIGHT
Solar panels are specifically designed to capture sunlight. However, the panels can still charge using other forms of visible light. Artificial light comes from many different sources, but on average, it is usually far less intense and effective when compared to natural sunlight.
While it may seem counterintuitive to charge an electric light with another electric light, there are some situations where this may be a benefit. For example, you can conserve energy by charging your solar lights inside your house while you go about your daily activities. Once the sun sets, you can simply place them back outside. Alternatively, you could charge your lights in a well-lit public place if you don’t have access to an electricity port or the Sun.
As far as ordinary household lighting goes, incandescent bulbs emit wavelengths that are the most similar to sunlight. Unfortunately, incandescent lights are becoming more and more uncommon as homeowners switch to more efficient LED bulbs. If you have an incandescent light in your home, try to place your solar panel as close to the light as you can.
The Importance of Lumens
Lumens are the measure of brightness. When charging a solar panel, you’ll want to pick an artificial light source that has the highest number of lumens as it will be the most intense. This intensity will ‘mimic’ the power of the Sun, helping to charge your solar panel as quickly and efficiently as possible
A rough way to estimate how many lumens a household bulb produces is to look at the wattage. Basically, a higher wattage equals more lumens. For reference, sunlight on a summer’s day measures out to about 10,000 lumens per square foot. The closer you can get to this number, the faster your solar lights will charge under your artificial light.
| Incandescent bulbs | Fluorescent bulbs | LED bulbs | |
| Lumens | Watts | Watts | Watts |
| 250 | 25 | 4-9 | 3 |
| 450 | 40 | 9-13 | 4-5 |
| 800 | 60 | 13-15 | 6-8 |
| 1,100 | 75 | 18-25 | 9-13 |
| 1,600 | 100 | 23-30 | 16-20 |
| 2,000 | 125 | 28-40 | 20-25 |
| 2,600 | 150 | 30-55 | 25-28 |
3. Indirect Sunlight
It may come as a surprise to learn that solar lights don’t actually need direct sunlight to charge. An indirect source can still provide some level of charge using your solar panels. If direct sunlight isn’t an option, a bright but shaded spot can work in a pinch.
One way to maximize efficiency with indirect sunlight is to place reflective surfaces or mirrors around your solar panels. These will help to direct more sunlight into your panels without having to physically move them. A mirror is the best choice, but a large, flat and white object can also work.
When using mirrors, pick some that are at least twice the size of your solar panels. This will ensure the panel is receiving as much sunlight as possible. It’s also recommended that you reposition the mirrors as the sun moves throughout the day.
Charging your Solar Lights in Cloudy Weather
It’s a cloudy and miserable day- there’s no way any sunlight is reaching your solar panels, right? No, not really. Regardless of the weather, quite a bit of sunlight can still manage to find its way to Earth’s surface.
When it’s cloudy outside, you can still get a decent or full charge for your solar lights depending on the size. On a particularly overcast day, solar panels are only around 20% as effective as they would be on sunny days. However, this is assuming there are no cloud breaks during the day, which is rare.
In inclement weather conditions, it’s recommended that you regularly dry your solar panels with a soft cloth. Precipitation can affect how much light your panels are receiving and may damage them if they aren’t fully sealed.
You should also angle your solar lights to face the sun directly as this will maximize your charging capabilities.
We have researched and tested the best outdoor solar lights. Here we talk about which outdoor solar lights rank the highest in different categories, in which numbers 2 and 4 perform the best on cloudy days.
3 Ways to Make Sure you are Getting as Much Charge as Possible
If you’re using your solar panels in sub-optimal conditions, like cloudy weather or with artificial light, you need to make sure that you’re harvesting every ounce of power available to you. After all, if you might be cutting it close on whether you’ll have light tonight, it’s best to do what you can to maximize your chances of a good charge.
1. Angle your lights
Angling your solar lights directly at the sun or artificial light source may give you that little bit extra to maximize your charge. While you may not always be able to move a fixed solar light that’s mounted to a wall or installed on a fence post, you should try to get creative as possible.
It’s important to note that the sun is at its strongest during midday. Keep this in mind when moving your solar panels as this can greatly affect how much your battery charges. If you put out your panels in the morning, don’t forget to reposition them in the afternoon and evening as well.
2. Keep your Lights at an Ambient Temperature
Temperature is another factor that affects the efficiency of photovoltaic cells. Extremely high temperatures are something that should be avoided at all costs as they can damage or decrease the efficiency of your solar panels.
Anything higher than 87 degrees Fahrenheit will result in a decrease in production of electricity. When installing your solar lights, avoid placing them on a dark surface as it will make the lights hotter during the day. If you’re using an indoor electric light to charge the panels, don’t place the solar light too close to the bulb as it will get too hot or pose a fire risk.
3. Keep your Solar Panels Clean
Removing any dirt or dust from your panels will help to ensure that light isn’t being blocked. A simple wipe with a bit of gentle soap, window cleaner, or some water will go a long way in terms of keeping your solar lights in good working condition.
Can you charge a solar light with a flashlight?
Yes, you can – artificial light (eg flashlight) is capable of charging your solar lights. The speed that the flashlight will charge the solar light depends on the brightness.
An average flashlight emits 100 lumens, so it will take much longer to charge your solar light as compared to being outside. As a comparison (in lumens), the average flashlight is 6.7% as powerful as a cloudy day and .1% as powerful as a sunny day!
So you don’t need sunlight for solar lights, but it definitely helps.
According to Philips (you know the lightbulb manufacturers):
Typical room illumination is 300-500 lumens, whereas outdoor light varies from 1500 lumens on a cloudy day to 100,000 lumens on a sunny day
https://www.usa.philips.com/c-f/XC000002361/what-is-lux
Read our related article, TOP 4 BEST Solar Flashlights For Emergency Use (Guide). We tested the best solar flashlights for emergencies!
Can You Charge A Solar Panel With A UV Light?
In theory, a small portion of the UVA band of light could charge a solar panel.
The UVA (315-400 nm) band of the UV light falls just within the Red visible light spectrum, it is possible that a small portion of that light could charge solar panels, but it would be significanlty inefficient. UV-A Blacklight with no filters on them are the only ones to use since they do not have a dark blue filter like other blacklight bulbs
Most UV light spectrum’s wavelengths fall below the spectrum that solar panels presently use. The UV spectrum covers the wavelength range 100-400 nm and as we’ve spoken in other parts of our article, The most efficient form of visible light for power production is within the spectrum of violet to red, or the wavelengths of 380nm (violet) to 750nm (Red).
