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Can I Charge a Solar Light with a Lamp? Or Direct Sunlight Only?

When we use solar lights, we always consider the placement of the solar panels. From the instruction manual of every solar product, we can see that professionals always mention that the solar panel must be placed in a position that can receive direct sunlight.

direct sunlight
direct sunlight is the best energy source for solar lights

But, even if we place the solar light in the position with the most sunshine, we can’t control the weather. For example, on a cloudy day with thick clouds, or in winter when the sunshine time is very short, will the solar light not work properly?? What are the requirements of lights exactly to charge a solar light?

In extreme cases, as stupid as it sounds and no one would do it, can we charge a solar light with a lamp?

Well, it’s not that simple.

Cloudy days
How can we do for the solar lights in cloudy days

How is solar energy converted into electrical energy?

Let's first understand the process of converting solar energy into electricity. The solar panel converts solar energy into electricity using the photovoltaic effect. This is a process in which light energy from the sun is absorbed by semiconductor materials (like silicon), creating free electrons and positive holes. The specific process is, that the photons contained in the light provide energy to the electron, and when the electron absorbs enough energy, it can become a free electron to generate an electric current. The free electrons are then carried through wires to a battery where they can be stored or an external circuit where they can be used to power various devices, including lights.


So, what happens if you try to charge the solar light with a normal lamp? Well, it won’t work. The reason is that the light produced by lamps is not powerful enough to generate electricity. The solar panel on a solar light is designed to work with sunlight, which is far more than 100 times brighter than indoor lighting. So if you try to charge the light with a normal lamp, the battery will not get enough power to store and release electrons from its surface. The same is true for solar panels on homes.

no power
if you try to charge the light with a normal lamp, the battery will not get enough power to store and release electrons from its surface

So how do we measure the intensity of light?

Which light is powerful enough to generate a large number of free electrons for the solar light to function properly?

Here we first introduce two concepts, lux and lumens.

Lux & Lumen
Lux & Lumen

1. Lux, Lux is a standardized unit of measurement of light level intensity, which is commonly referred to as "illuminance" or "illumination". We can use the lux to compare the energy of light. A measurement of 1 lux is equal to the illumination of a one-meter square surface that is one meter away from a single candle.

2.Lumen is a measure of the total quantity of visible light emitted by a source per unit of time.

Relation between lux and lumen
Relation between lux and lumen

The relation between lux and lumen is Lux = Lumen/ Area. In other words, when the size remains the same, the light intensity is proportional to the lumen. At the peak of the luminous efficiency function (555 nm), 1 lumen is 4.09*10¹⁵ photons/s. As we mentioned above, the photons provide energy to the electron. So we can say, if the size of the solar panel remains the same, when the lux of the environment is larger, there will be more photons that can provide energy for the electrons and generate current. As a result, the current will be higher, and it will take less time to fully charge the battery.

Next, let's look at lux in different environments.

Lux in different light conditions
data from greenbusinesslight

The amount of light that comes from the sunshine can range from a few thousand lux to a few hundred lux, depending on the time of day and the weather. Artificial interior lighting, in comparison, has significantly lower lux levels, often 1000 lux or less.

lux in different light conditions indoor
data from greenbusinesslight

In general, the higher the lux level is, the faster you can charge your battery. For example, a sunny day on the beach can have around 100,000 lux, while an overcast day in the city might only have 1,000 lux. The difference in light intensity can affect how quickly your solar panel will charge your device.

Now, back to the question posed at the beginning of this article, can we charge a solar light with a lamp?

According to the chart data, the lux of direct sunlight is 32,000 to 100,000, while the lux of indoor lighting is about 500 when we refer to the office lux. That is, when the size of the solar panel receiving the light remains the same, the photons received in direct sunlight are 64 to 200 times more than those received in office light. So if you can handle a fairly long charge, you can use a desk lamp to charge a solar product, but I bet you'll lose patience in the process.

How many hours do I still need to wait for?

Then, do solar lights work in the shade?

Shades in the Garden
Shades in the Garden

The lux in the shadow is close to the lux of sunrise and sunset. From the chart, we can see that the lux of sunrise and sunset is about 400, which is less than the lux of office lights, and the charging speed is slower. Therefore, we also do not recommend charging solar lights in the shade.

However, what if I want to use solar lighting indoors? How to charge solar lights indoors?

There are two types of solar lights on the market, solar light with a built-in solar panel and solar light with an external solar panel.

The first type of solar light requires direct exposure to sunlight, which means it can't be used indoors unless there is a window that receives direct sunlight.

The second type of solar light has an external solar panel that can be easily moved. This means you can charge the light indoors if you can put the solar panel under direct sunlight, for example, on a patio or balcony.

OK, now, you know how to charge the solar lights indoor and the feasibility of charging them under a lamp.

Then, how many charging hours do solar lights need?

How many hours does it take to charge the solar lights

The answer is, it depends. When the power of the light-emitting device is the same, the amount of light a solar light can produce is dependent on the battery capacity. The battery capacity is fixed, but this value will gradually decrease over time. Without considering the loss of battery capacity, to measure the charging time, it is mainly to compare the amount of current per unit time. The greater the amount of current per unit time, the shorter the charging time required. Therefore, if we want to increase the efficiency of charging, we can use larger solar panels, which can receive more photons per unit of time; also, place the solar panels in direct sunlight as much as possible.

Hope everyone can get some knowledge from this article. If you want to know more about solar lights, please check our other blog posts about more principles of solar lights and solar light decoration ideas.

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