The Ultimate Guide to Solar Lights and Solar Photovoltaic Lighting Systems

Solar photovoltaic lighting systems are simplified, low-power, off-grid photovoltaic systems gaining popularity in various applications for illuminating outdoor spots, including for security and safety reasons.

Probably you often hear or read questions such as “Are solar lights any good?” or “Are solar lights worth it?”

This article provides essential info on why solar lights are becoming more and more popular, and also:

  • How solar lights work?
  • What is a solar lighting system?
  • What is a solar light bulb?
  • Which solar lights are the best?
  • How solar lights work at night?
  • Will solar lights work in shade?
  • Why do solar lights need batteries?
  • Where are batteries in solar lights kept?

And more:

  • Are solar lights safe?
  • Will solar lights charge on a cloudy day?
  • Where is the solar light sensor hidden?
  • Why solar lights are preferred for outdoor use?
  • Can solar lights work indoors?
  • Can solar lights charge through windows?
  • Can solar lights work in winter?

Apart from providing detailed answers to these frequently asked questions, the article offers a short guide on what solar lights to buy and which solar garden lights are the best.

So, let’s get started!

Introduction to solar lights and solar photovoltaic (PV) lighting system

In solar lights and a solar photovoltaic (PV) lighting system, the solar energy is converted into electricity and stored in a battery used to power a bulb (usually LED one) during the evening and night hours.

Solar lighting systems are known for their high energy efficiency, high reliability, lack of maintenance, and substantial practical value.

LED lights are preferred due to their higher energy efficiency than traditional incandescent light bulbs – a LED lamp consumes five times less power to provide the same amount of useful light than a conventional incandescent bulb!

How are solar lights powered?

A PV panel receives solar irradiation throughout the sunny hours of the day and converts the solar energy into electrical energy stored in the battery.

In the evening, the battery starts discharging by rendering its stored power to the LED light source(s).

In solar lights, the controller acts more as an “intelligent controller” than a pure battery charge controller.

Apart from preventing the battery from overcharging and over-discharging, it takes care of providing the proper power to the light sources and adjusting their illuminance.

When the evening is near, the lights usually are turned on by a dark-detecting circuit (solar light sensor) that is often integrated with the controller itself.

As we mentioned before, in solar lighting systems, LED lights are frequently used, as they provide more brightness and higher energy efficiency than traditional light bulbs.

Here are some applications where solar lights are used:

  • Traffic lights and street lights
  • Park lawn and garden lights
  • Public transport billboards
  • Parking lots
  • Guarding remote properties and areas
  • Construction sites
  • Security or safety lighting of restricted-access areas
  • Temporary lighting needs or as backup lighting where wiring might be vulnerable due to possible theft or copper cables damage.

Why are solar lights good?

Solar lighting systems are becoming increasingly popular, as they:

  • Can operate as long as installed in a spot capable of receiving direct sunlight.
  • Are highly efficient – solar lights are a cost-effective solution if you need to have your garden fully illuminated at night.
  • Are easy to install. Solar lighting systems do not need trenching and installing cables, which makes them cost-effective immediately after buying them. With solar lights, you are not bound to the existing wiring and have the freedom to install them wherever you like and as many ones as you want. Installing a solar lighting system usually takes a couple of hours. To compare, installing traditional electrical lighting, where wiring can often be a challenge, takes days and even weeks. Also, with solar lighting, you need the minimum set of tools and equipment.
  • Are safer – they are not connected to the mains.
  • Are practically maintenance-free – you should only replace the battery once every 3-4 years or even more for lithium-ion batteries. The other components last much longer.
  • Are suitable for indoor (solar sheds or solar desks) and outdoor (illuminating home gardens and lanes, decorating home terraces or backyards, public parks, streets, parking lots, emergency lights, camping lights, traffic lights, etc.) applications.
  • If you have garden lights with a pointed base designed to be pushed into the ground, you can easily change their location if you are not happy with your garden or yard’s lighting configuration and install them in a sunnier place.
  • Can save you money and lower your electricity bills, as they are “connected” to an unlimited energy source rather than the local utility grid. Thus, a solar lighting system is not vulnerable to rising energy prices.
  • Are fully independent of the AC grid power – with solar lights, you have no blackouts.
  • Look aesthetically and come in a variety of shapes, sizes, colors, and designs.
  • Are environmentally friendly – as a renewable energy source, solar panels do reduce the global carbon footprint, recognized nowadays as a significant environmental problem.
  • Run automatically – due to the dark-detecting circuit (solar light sensor), no manual turning on/off is required.
  • Are resistant to adverse weather conditions – rain, snow, hail, fog. Also, they fit any kind of climate, whether hot or cold.
  • Have a long lifespan:
    • Solar panels last about 20 years,
    • A battery can last between 3 and 10 years,
    • A LED lighting source has a lifecycle of between 50,000 and 100,000 hours.
  • Solar kits sold online offer an additional 5V USB-socket for charging mobile phones and other USB-compatible devices.

When solar lights can be a challenge?

Unfortunately, solar lights are not as cheap as traditional lighting sources.

The main reason for the relatively high upfront cost is PV lighting systems’ price, which is still relatively high – between 10 and 20 dollars per light.

One of the main reasons is photovoltaic panels’ cost, which is steadily going down but not fast enough.

The higher cost of solar lights is also a result of the LED lighting sources and sealed batteries, which are more expensive than conventional light bulbs and lead-acid batteries.

If more costly lights (for example, halogen ones) or batteries (such as lithium-ion ones) are used, the price can go even higher.

Also, when installing a solar lighting system, here are some significant issues to consider:

  • The daily amount of sunlight in your area is essential. A solar light provides you with maximum efficiency as long as solar panel cells receive enough sunlight every day.
  • If a solar light is installed in a spot getting a low amount of sunlight, it is supposed to operate for a daily period shorter than recommended by the manufacturer.
  • Solar lights are rarely installed on roofs. Thus, they are much more prone to shading than traditional residential or mobile (RV or boat) solar panel systems. Shading dramatically reduces solar-generated electricity and poses a risk of regular undercharging the battery, thus worsening its performance and shortening its lifespan.
  • Some solar lights come as a single all-containing unit that needs to be mounted in an unobstructed and unshaded spot. Luckily, there are solar lighting systems offered as two separate units – the solar panel and the remaining items (the battery and the controller). In such a case, only the PV panel is supposed to be mounted in a sunny location.
  • Wind force might be a problem in windy regions. Therefore, it is vital to design the solar array’s mounting system to withstand the maximum expected wind speed in your area.

What are the major components of the solar lights and solar lightning systems?

Here is a simplified picture of a solar lighting system:

solar lights components diagram

Solar panels

The solar panel produces electricity even on a cloudy day. In such a case, however, the solar-generated electricity is less than on a bright sunny day.

The battery is sized to store electrical power for a couple of days without getting a full charge.

At night, the solar cells do not produce power.

The dark-detecting (solar light sensor) circuit turns on the LED light, which consumes the battery-stored electricity generated by the solar panel during the daytime.

The solar light sensor measures the amount of ambient illuminance and turns on the light once the illuminance has fallen below a certain level.

A PV panel for a solar lighting system differs from the traditional large solar panel, since it comprises four solar cells.

PV panel consist of solar cells connected in series to produce a higher voltage.

A single solar cell converts sunlight into electricity by generating current, which is called “photovoltaic effect”.

The amount of electricity depends on the solar light intensity, whether the location is exposed to direct sunlight, and how long it can access sunlight.

Solar Battery

Although being the least expensive option, flooded lead-acid batteries are avoided in solar lighting systems.

They are not maintenance-free and are risky to operate with, especially during transportation and handling.

For this reason, mostly sealed batteries are preferred.

A sealed battery is rechargeable and has to be replaced every couple of years.

 In a solar lighting system, the battery is the only component that needs to be replaced relatively often.

The solar panel and the electronics (the solar light sensor circuit and the controller) have a much longer lifespan. With a fully charged battery, a solar light can operate up for to 10 hours.

Every battery is sized based on “Days of Autonomy”.

This is the period the battery can stand without getting a full charge from the PV panel. It can be 3 to 5 days, depending on the typical number of cloudy days per month.

Nowadays, solar lights are typically powered by one of three possible different battery types.

Here is how solar light batteries can offer you various benefits or drawbacks, according to their kind:

  • Nickel Cadmium (NiCad or NiCd) – one of the oldest and the cheapest battery technology. NiCad batteries are known to stand extreme cold and heat. Over time, however, the battery utilizes less and less of its full capacity. This is the so-called “memory effect”. It should always be considered as the result is the battery end of life coming shorter than expected. The typical lifespan of NiCad batteries is about two years of operation.
  • Nickel Metal Hydride (NiMH) batteries last up to 40% longer than NiCad ones, but they are quite vulnerable to extreme temperatures, which can dramatically shorten their lifespan. Also, NiMH batteries are less susceptible to the memory effect.
  • Lithium-Ion (Li-Ion) batteries are the most expensive but also the most durable ones. They are known for their small size and lack of memory effect. Although the cost of such batteries is steadily going down, they present some risk due to their chemistry and production methods. Unfortunately, such volatility means is related to fire hazards. Nonetheless, all laptops and mobile phones today come with exactly li-ion batteries.

There is a diode between the photovoltaic panel and the battery, preventing the current from flowing from the battery to the PV panel at night.

The battery voltage (also known as “system voltage”) is typically 12V. 6V or 24V, however, are also possible.

Charge controller

The primary function of the charge controller is to prevent the battery from overcharging and over-discharging.

Also, it protects the solar panel at night by preventing the reverse current from flowing from the battery to the panel.

Finally, it regulates the voltage and current supplied to the LED light so that the latter cannot blow up.

The charge controller is supposed to act as an intelligent controller.

It manages all the three remaining components – the battery (by preventing overcharging and over-discharging), the photovoltaic panel, and the LED lighting (by performing light control and time control). Generally, 12V PWM charge controllers are preferred as a more cost-effective option.

Solar lighting source

Solar light bulbs or tubes are usually LED light sources. High-powered LEDs are cheaper, but their current rating is higher, and they also produce more heat than regular LEDs.

The daily period of operation can be between 6 and 10 hours, depending on the season. LED lights can last up to 10 years before they need to be replaced.

Also, LED light bulbs are reported to last up to 100,000 hours of operation.

The moment to change a solar component (whether the battery, the light, or the PV panel) has come when your light has dropped in performance and cannot maintain its usual illuminance at night.

Which solar-powered lights to select for your case?

Outdoor solar lights

Outdoor solar lights are divided into two main groups:

1) Solar lights for aesthetics and coziness – these look well in your garden or backyard, are suitable for gathering, etc. Usually, they have lower luminance since they are not intended to illuminate an area entirely.

2) Solar lights for security and safety – they are supposed to light up a spot during the whole night – construction sites, parking lots, front or back porches. Often they come with motion sensors.

The below list is an example that outdoor solar lights come in a great variety of sizes, designs, and intended use.

  • Solar string lights – used to illuminate and decorate porches, fences, trees, posts, etc.
  • Solar deck lights – for walls and stairs. They are a perfect solution given both cost-savings and aesthetics since you don’t need to lay wires along walls and stairs. Solar step lights are similar to solar deck lights.
  • Solar post lights – used for decoration and lighting up the outdoor environment, such as parks, gardens, streets, and driveways.
  • Solar fence lights – similar to solar post lights and solar porch lights. They usually come as “solar string lights.”
  • Solar umbrella lights – for your garden, deck, or balcony.
  • Solar lawn lights – come in a variety of shapes and colors for your garden or lawn.
  • Solar camping lights – sold as portable or foldable solar kits for use in remote outdoor areas.
  • Solar path lights – for walkways and garden lanes.
  • Solar spotlights – to be mounted near doors or driveways, and also in gardens.
  • Solar lighthouses – exceptionally modern for solar gardens, solar lawns, or yards. They are used both to illuminate and to decorate.
  • Solar lanterns – resembling solar post lights, but compact and portable. For this reason, they are convenient accessories not only for your household but also while camping away from your home. What is more, they are an individual PV panel system that is not a part of the mobile PV system and does not depend on your leisure battery.
  • Solar candles – can be regarded as a perfect replacement for traditional flame lights. Apart from looking lovely, they are also much safer than conventional candles. Also, unlike the latter, solar candles are ideal for outdoor mounting, where safety is a significant issue.
  • Solar spotlights – usually put at a height with the purpose to fully illuminate an area or a spot that should be lip up with for a particular purpose – parking lots, construction sites, etc. For such cases, you are likely to choose brighter lighting sources.
  • Solar floodlights – used to illuminate specific areas, often for security or safety reasons. In such cases, the mounting height, type, and light intensity of the lighting source are critical. Solar floodlights are often installed in areas with no electricity nearby.
  • Solar streets – a part of the local infrastructure in towns and cities. Although the initial investment is higher, you will have no electricity bills, no carbon footprints, and no maintenance. 
  • Solar parking lot lights – often a part of industrial infrastructure, where aesthetics is not such an important issue as in parks and gardens. Therefore, if you need, you can use a larger solar panel and hence a bigger battery.
  • Solar traffic lights – an ideal solution in natural disasters that might lead to power outages and traffic disturbances.
  • Solar emergency lights – suitable for areas where frequent power outages occur.

The brightness of a solar light depends on the battery charge, and the latter generally depends on how much direct sunlight the solar panel has received during the day.

How much of your area will be illuminated also depends on the solar panel’s quality and the lighting source itself. Solar panels and solar lights of higher quality cost more but provide you with more light and last longer.

Indoor solar lights

Indoor solar lights are similar to outdoor solar lights, as they are based on the same principle of operation and are offered in various shapes and designs.

Unlike the lighting source itself, however, the solar panel is located outdoors, usually on the top of the building.

  • Solar shed lights – typically located far from the house and are usually not well illuminated, often because homeowners are not eager to run lots of separate cables in the shed and install lights that make the monthly utility bills go up. Such lights can also be well combined with motion sensors to avoid installing a power switch that might be quite difficult to come across in the dark.
  • Solar desk lights – an ideal solution if you spend hours at a writing desk, as long as the illuminated light is in the milder part of the spectrum.

Why is color temperature critical?

Lighting color is measured in color temperature, according to Kelvin’s scale. The lowest end of the Kelvin spectrum is red (1,000K or the longest wavelengths), and the highest end is blue (10,000K or the shortest wavelengths).

The below table shows the most popular lighting sources’ color temperature, both natural and artificial ones.

High-pressure sodium bulb2,200K
Warm white seesmart LED2,700-3,200K
Incandescent light 100W2,800K
Halogen light 100W3,000K
Tungsten light3,200-3,400K
Quartz light3,200-3,500K
Fluorescent light3,000-4,000K
Natural white seesmart LED4,000-4,500K
Direct sunlight4,800K
Electronic flash5,000-5,500K
Average sunlight5,500-6,500K
Noon sunlight6,000-7,000K
Cloudy sky or shade6,500-8,000K
Cool white seesmart LED7,000-7,500K
Clear blue sky10,000K
Table of the color temperature of the most popular lightning sources

For outdoor applications, lights above 3,000K are typically used, often in the range of 5,000-7,000K.

The higher the number, the colder the color, since it is in the blue-white spectrum.

Also, it is well known that the human eye prefers warmer colors (i.e., the ones in the lower part of the scale), and for this reason, colors of temperature below 3,000K are ideal for indoor lighting purposes.

The warm colors of the spectrum make the environment look cozy and inviting. Light sources above 5,000K, however, are known to operate with much higher efficiency.

They might, however, not look as welcoming as the warm colors. Still, they offer another benefit – the effect is as though they affect our mood in a refreshing, stimulating, and energizing manner.

Which solar lights last the longest?

Now, this is kind of a tricky question.

We want to stress here that you are expected to take care of your solar lighting system to prolong its lifespan as much as possible.

As solar lights are traditionally located outdoors, you should be aware of the fact  that the degree of how clean solar lights  are play a significant role in the illuminance you get.

How to clean solar lights?

Also, you should know what to clean solar lights with.

Dust, dirt, mud, or bird droppings can significantly reduce the solar-generated electricity in any photovoltaic system.

In the case of solar lights, you will have lower illuminance than usual.

It would be best if you cleaned your solar lights with a damp towel (a paper one is also okay) by carefully wiping the surface to remove the dirt.

To remove more stubborn stains, you may use warm water and dish soap; a chemical detergent is not needed.

All this is valid for the solar panels as well.

As we already mentioned, photovoltaic panels and electronics have a longer lifecycle; the only components that are to be replaced or repaired are the battery and the lighting source.

Any lightbulb, even a LED one, can be easily removed by unscrewing the attaching mechanism.

The batteries can be either recharged or replaced.

When charging a battery or replacing it with a new one, above all, beware of the polarity – positive or negative terminal should be connected to the cabling marked as “+” or “-” respectively.

Also, never lift a battery by holding it by the terminals, and be careful not to short-circuit them.

How to fix solar lights?

Now, this depends on the specific problem you are experiencing.

For example, your illuminance might have deteriorated due to dirt and dust accumulated, whether on the PV panel or the lighting source.

Also, your battery might be near the end of its lifecycle.

For solar lights, this means 3 to 4 years.

Last but not least, you should have a look at the object surrounding the solar lighting system. If a shade-throwing obstacle has appeared nearby, the solar panel will not generate as much electricity as before.

The battery cannot be fully charged, which results in a reduced duration of daily illuminance.

You are supposed to remove the obstacle.

If you are having issues with one of your lights, check the battery and clean off the panels to see if that eliminates the problem before you go looking to purchase a new one.

Above all, you should only install your solar lights at a spot where they would be capable of receiving the maximum amount of direct sunlight during the brightest part of the day, i.e., throughout the sunniest hours.

Receiving direct sunlight for eight hours a day is enough to provide a full charge so that the lamp would illuminate all the evening.

Why solar lights stop working?

One of the reasons why solar lights stop working is the lack of enough direct sunlight.

A solar light battery needs 5-6 hours of sunlight daily to get charged.

If the solar light is placed in a shade or turns to be shaded by an obstacle – for example, building or trees, the battery cannot get sufficient charge, and the lamp might not be capable of operating all night long.

Another issue when solar lights stop working is if the battery has come to an end.

Each battery has its lifespan. Every couple of years, you should check the batteries and measure the battery voltage, mostly if a noticeable drop in the illuminance occurs.

It would be best if you did not wait until a solar light battery starts to leak and erode, as this might damage the other electric or electronic components located close to it.

Although often overlooked, the next possible reason for solar light failure is a faulty solar light sensor – the device that reacts to dark and turns the light on in the evening.

With a non-operational sensor, the light will not be able to differentiate between day and night. An easy way to diagnose the problem is to cover the sensor with your hand.

If it is okay, the lamp will turn on; otherwise, you should replace the sensor if no other issues are visible.

As a last resort, you should make sure that there is no street lamp or other lighting source in the closest proximity.

Otherwise, the light will never be able to turn on at night.

To cut a long story short, you will know how to repair solar lights if you know why they fail.

Most often, they stop working due to either dirty solar panels or dying batteries. So, you should take care of both the solar panels and the lights.

Are solar lights safe?

One of the reasons why solar lights are considered safe is that they operate in the 12V range.

You can find this voltage can be found everywhere around you. T

hese 12 volts are safe for people and are used in various toys or household devices.

Moreover, solar lights are much safer than any fire-operated appliances, such as candles or petrol lamps.

Another reason for feeling safe with solar lights is the lack of external wiring, which minimizes the risk of getting an electric shock or getting stumbled. Finally, solar lights are not prone to overheating, and this is a great advantage making them different from the standard incandescent bulbs. 

Can solar lights catch fire?

This is one of the frequently asked questions when discussing the solar light safe operation.

The truth is that solar lamps are exposed to the risk of catching fire, mostly when operated by lithium-ion batteries.

The latter contain lithium that is generally a highly reactive and combustive metal.

Combined with flammable organic solvents in each lithium battery cell, it can combust when exposed to heat.

However, the good news is that any lithium battery cannot do without a smart controller monitoring the state of charge and the other battery parameters.

 These also include the temperature.

Therefore, if a fault is detected, the battery controller will disconnect it from the other circuit component, thus preventing the hazard.

Even reputable battery manufacturers used to have problems with lithium batteries before things settled.

Unfortunately, placing a solar lamp somewhere in a heated environment is not the only possible source of problems.

Another issue might be a defective solar light bulb, causing the battery to overheat and get damaged.

For this reason, our advice to you is to avoid buying cheap solar light components, as they always bring the risk of fire.

Yes, although affordable, solar components are not cheap. However, keep in mind, that a low-priced solar system means low quality and unreliability, and this is valid not only for all the components but also for the way they’ve been assembled.

No matter how many positive reviews you see on, we do not recommend buying cheap solar light equipment produced by an unknown Chinese manufacturer.

Instead, it would help if you referred to a reputable solar light vendor.

 Remember, your lights are to be mounted outdoors and exposed to any adverse weather conditions.

Are solar lights waterproof?

Solar lights are exposed to a risk of water ingress, which poses a hazard for the circuitry, especially some sensitive electronic components.

However, if the solar light system is appropriately designed and manufactured, such a risk is minimized.

For this reason, it is essential to choose solar lights from a reputable manufacturer rather than plumping for the first cheap devices found online.

Respected solar lighting vendors always offer a fair warranty with their products, also covering damages resulting from water ingress.

If you ask, “When do solar lights work with water in?” the answer is “Never”.

Water penetrated inside the solar lamp due to a damaged or weakened sealant can prevent the light from operation.

Although solar lights are produced waterproof, sometimes they might not withstand heavy rainfalls, and the electric circuitry might get temporarily damaged.

If a solar lamp is filled with water, you should disassemble all the components, dry them off, and put them back together.

Although solar lights are designed for a large enough temperature range, you should avoid leaving them outdoors during severe winters with cold, snow, and ice.

No matter how well designed, exposing solar lights to extreme weather conditions, apart from posing the apparent risk of direct damaging, also shortens the lifespan of both the lighting system and its components. 

Can solar lights stay out in winter?

This question gives rise to other two ones – “Are solar lights any good in winter?” and “How do solar lights work in the winter?”

 Solar lights operate all year round, although summer has the highest number of sunny hours. On the other hand, there is sunlight even on cloudy days, even in winter.

It is well known that solar systems use the sun’s light to operate rather than the sun’s heat.

So, as night is the only time when PV panels cannot produce electricity, your battery will be charged, regardless of the weather.

On cloudy days, it is not likely to get a full charge, and therefore, your solar light will illuminate for fewer hours. However, low temperatures in winter can severely reduce the lifespan of your solar batteries (especially NiMH ones).

Considering also the risk of reduced illuminance, we recommend you dismantle your solar garden lights in winter and put them back in the ground in spring.

If now you have found the question “Will solar lights work in winter?” a bit pointless, please, do not forget that what also matters is under what conditions solar lights work in winter.

The first thing to do is change the orientation of the photovoltaic panel. Since the sun is lower in the sky and nearer the horizon in winter than in summer, the solar array needs a higher slope (tilt).

Next, you should avoid shadows.

Don’t forget that in winter, objects cast longer shadows.

Therefore, you are supposed to relocate your panels so that the solar panel performance, hence the light illuminance, is not impaired.

Remember, your task is to find a position where your panels get the maximum sunlight, regardless of the season.

In case of fewer Peak Sun Hours (PSH) per day, what also matters is the panel efficiency. For this reason, we advise you to choose crystalline photovoltaic panels rather than amorphous ones.

The proper tilt helps the solar panels get the maximum sunlight and get rid of the accumulated snow more easily.

If you live in the Northern hemisphere (e.g., the US, UK, Canada, Europe, India), your solar panels should face South, preferable at an angle of 60 degrees.

If you live in the Southern hemisphere (e.g., Australia, New Zealand, South Africa), the same tilt angle is valid, but the panels should be facing North.

If you live in a snowy area, the answer to the question “will solar lights charge in winter” depends on how often you clean the snow off the PV panels and lighting sources.

Can solar lights charge in the shade?

Solar lights can be charged by artificial light but not as efficiently as when exposed to direct sunlight.

The same is valid if you try to charge the battery in the shade. In other words, it takes much longer for the battery to get fully charged, since if not placed somewhere in the sun, the PV panel would generate less electricity.

You also have less solar-generated electricity on a cloudy day, as well as when your panel is covered with a thick layer of dirt or dust.

All these prevent the photovoltaic cells from operating normally and generating the maximum amps possible.

Can solar lights be charged indoors?

Such a question might seem somewhat weird – how on earth will SOLAR lights charge indoors with no sun shining at home?!

Yes, solar lights are typically intended for outdoor use, which means that they are supposed to be charged by the sun.

Sunlight is the most natural and efficient way to charge your solar lights’ batteries fast and easy.

However, this does not mean, that solar lights can never be charged by an artificial light indoors.

What do you think, will solar lights work indoors always with no problems?

Here lies the key to the kingdom.

The truth is that solar panels “get used to” artificial light, so our advice is to charge your solar lights indoors as a last resort only or, at least, just sporadically.

Though not energy-efficient per se, incandescent light bulbs should be preferred to LED or halogen lights, as they can charge the solar panel faster.

Can solar lights be charged with artificial light?

There are ways to charge your solar lights without direct sunlight, using artificial light.

You can do that by using a typical incandescent light bulb.

 Unfortunately, this is much less effective than getting a charge from the sun, so you should be prepared to wait longer.

How much longer depends on the wattage of the incandescent lamp – the brighter the bulb, the faster the charge. 100 watts are considered as a needed minimum.

 Indeed, this makes sense mostly for solar lights with smaller PV panels.

What also matters here is the distance between the artificial light and the solar panel.

You should place the panel close to the lamp – 20 inches (51 cm) are okay

. Otherwise, charging would take longer.

Apart from incandescent bulbs, you can also use LED or halogen lights to charge your solar panels.

If you use LED lights, usually this takes twice longer than using direct sunlight on a bright, sunny day.

The result is that your solar light would be capable of lighting your area for up to 8 hours.

You should also be aware that the UV part of the spectrum makes solar panels operate and charge the battery.

UV lamps, however, are not recommended for charging, as they generate more heat, which is not acceptable indoors.

 Furthermore, they pose a safety hazard for humans.

Nevertheless, incandescent, LED, or halogen lighting sources generate enough UV light capable of charging the solar panel, although taking longer.

As you know, solar panels can get charged even on cloudy days, where solar irradiation might be less than on a sunny day.

However, they can still be capable of making solar panels generate electricity.

Yes, the drop in charging efficiency is significant (between 50% and 70%), but the solar panel can still charge the battery.

Although less efficient than monocrystalline or polycrystalline solar panels, amorphous panels collect more light on cloudy days due to their nature.

Finally, every solar light battery is sized for certain days of autonomy (DoA, mentioned above) indicated in the technical specification sheet. “2 days of autonomy” mean that the battery can make the light illuminate even when the solar panel has not received a charge for two consecutive days.

Can solar lights charge through windows?

Solar lights use the electricity generated by solar panels.

These panels work best when exposed to direct sunlight, but they can also be charged through windows.

A solar panel gets the fastest and the best charge when placed on the window sill, thus directly facing the sun.

Unfortunately, if you have a tinted-glass window, this makes the charging process slower and less effective.

This is also valid for double and triple glazed windows – every layer of glass reduces the charging efficiency and requires longer for the battery to get a full charge.

The first reason for the reduced efficiency when charging a solar panel through a window is that a part of the sunlight is reflected by the glass and lost until it reaches the solar panel behind the window.

Another critical issue is the angle between the rays of the sun and the solar panel’s surface.

By the way, this is also valid for solar panels installed outdoors.

Always when a solar panel is mounted at a non-optimal angle, the solar-generated electricity decreases.

Are solar lights bad for wildlife?

It is alleged that most forms of artificial lighting, including LED and halogen light bulbs, affect wildlife.

Such disruptions might include, for example, disorientation of moths, blinding or attracting frogs, making garden birds singing before dawn, or disturbances in the breeding cycle of other animals.

Also, it is believed that artificial light pollution is the main reason why glow warms are so rare nowadays.

The truth, however, is that solar light cannot kill animals.

What is more, there are some ways to minimize the impact on wildlife. For example, you can position your garden solar lights relatively low, turn them off while not in use, or choose solar light bulbs emitting in softer colors, i.e., yellow or warm white rather than cold white or blueish.

Are solar lights bad for plants?

Lots of people planning to build a solar garden reasonably ask this question. Often outdoor solar lights are used to uplight garden trees – that is, to direct the lighting sources mounted on the ground upwards, thus illuminating the trees.

The light from the solar lighting sources is similar to the sunlight, since it is in the same visible spectrum but of less intensity.

Infrared (IR) and ultraviolet (UV) lights can be harmful, since they adversely affect photosynthesis, vital for all plants and trees. However, typical outdoor solar lighting systems radiate very little or no IR or UV spectrum at all, as they typically radiate in soft colors and are intended for what is called “mood lighting”.

Moreover, most LED light bulbs are designed to minimize IR or UV emissions as much as possible.

How to select the best solar lights for your garden or backyard?

Which solar lights are the brightest does not lead to a simple and straightforward answer, as there are a couple of factors intertwined:

  • Location. There is no such stuff as a “universal solar lighting solution” that can be applied anywhere, on any site worldwide. Solar irradiation varies geographically, and so does the solar panel yield and the solar-generated electricity.
  • The area you need to illuminate. For example, it is not the same business case if you want to install LED bulbs along your garden lanes or need a strong light source to ensure your parking lot or home entryway’s safety. Each case has its required light levels (see the lumen reference table below). What also matters is the size of the target area.
  • Light source operating profile. If you design a strip of LED lights for your garden lanes, they are only likely to run during the evening hours. Indeed, this is not applicable if you are to illuminate an area for safety/security reasons that is supposed to be lit up all night long.

Here are some steps we suggest upon buying a solar lighting system. This guide is universal, no matter whether you have already decided which solar lights would be the best match for your garden or backyard.

1) Surveying and analyzing your site

Above all, before starting with questions such as which solar garden lights or which solar security lights are the best, you should have a thorough look at your location.

The place to mount the solar panels should be directly accessible by sunlight. This is also valid for indoor lighting systems, where longer cables are to be run between the PV panels (that should be mounted on the roof) and the remaining components.

It is not necessary to mount the solar lights in a sunny place.

The area you will illuminate might be located in a full shade, which is okay as long as you mound your photovoltaic panels where they can be accessed by direct sunlight. Your lights will still operate in case of insufficient solar irradiance, but will shine less brightly than usual.

2) Finding what exactly you need.

This means including all the solar lights you need, specifying at least the type (LED, halogen, etc.) and each lighting source’s wattage.

Above all, you should search what illuminance is the most suitable for the area you are to light up.

For example, you won’t need a powerful light for your shed or your garden, but you are likely to need a much brighter lamp for your parking lot or the construction site of your holiday home that is being built.

During such an analysis, you can benefit from the following rules of thumb:

– 100 lumens are suitable for lighting up parking lots, construction spots, or commercial sites, where safety and security are often needed.

– 75 lumens are enough to illuminate an outdoor meeting, parties, or other group events, where lights are supposed to be neither intrusively bright nor teasingly dusky.

– 50 lumens are perfect for walkways, fences, driveways, backyards, gardens, lanes, and other relatively small locations. For these spots, solar lights are intended to add mood, color, and dimension rather than lighting up the area.

Here is a match between the above-recommended lumens and the wattage, depending on the lighting source type:

 Halogen lamp, WFluorescent lamp, WLED lamp, WHigh-pressure sodium vacuum lamp, WMercury vacuum lamp, W
100 lumens5210.82
75 lumens3.751.250.80.651.5
50 lumens2.50.850.60.41
The table about the connection between the wattage of lightning sources and recommended lumens

3) Searching and finding the highest quality solar lights

This means selecting your solar light vendor.

Again, similar to residential or RV solar panel systems, it is vital to determine whether the product can provide what is written in its specification and whether it is offered with a good warranty.

Like when you buy any of the solar components for either a grid-tied or an off-grid photovoltaic system, you expect to get the best value for the price.

As we usually do for various kinds of products, vendors, or services, you should search as much as you can for positive reviews that might be available online.

Solar lights in summary:

A solar lighting system:

  • Receives sunlight during the day and convert it into electricity,
  • Stores the electricity into a battery, and
  • Converts the battery-stored electricity into light and release it at night

The major components of a photovoltaic lighting system are the solar panel, the battery, the charge controller, and the lighting source. Solar lights offer a lot of benefits, which explains why they are gaining popularity in recent years despite the still relatively high upfront cost.

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How To Choose The Right Solar Lights

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Lacho Pop, MSE, holds a Master's Degree in Electronics and Automatics. He has more than 15 years of experience in the design and implementation of various sophisticated electronic, solar power, and telecommunication systems.  He authored and co-authored several practical solar books in the field of solar power and solar photovoltaics. All the books were well-received by the public. You can discover more about his bestselling solar books on Amazon on his profile page here: Lacho Pop, MSE Profile