Introduction: How to Convert an Outdoor Solar Light to an Inside Night Light

About: I am a retired analytical chemist living with my wife Cynthia in Cornwall, south west England. I have held the UK radio amateur call sign G3PPT since 1961. I have been interested in computing since the days …

Garden Solar lights have been with us for some years now and many must have wondered if these could be made to operate indoors and used for nightlight duty. The mechanical structure of these items has not hitherto been conducive to such use and the light levels inside a dwelling are usually far too low to meaningfully charge the storage battery. However there is a unit now being sold under the description "Crackle Ball Hanging Lights" which are very compact being free of the usual earth stake. This article shows how these can be made to function indoors by the simple expedient of having the unit inside the room whilst a duplicate solar cell is connected in parallel and placed in a window facing outside. There is an added advantage in that the existing solar cell turns off the unit when there is artificial light thus saving battery power.

You will need fine cutters and pliers and a small soldering iron as the modification whilst simple electronically is very fiddly.

In addition you will need wires fine enough to wedge under where the globe enters the assembly as shown in the picture above and I used two cores of four cored telephone cable.

Lastly you will need a 2 Volt Solar Cell. These are available from on line sources and I used a 2 Volt 100mA encapsulated unit from:

Alternatively you can use an item salvaged from an old garden light but it must be a 2 Volt item.

Step 1: The Solar Light Before Modification

The first picture shows the unmodified unit. A glass globe with a crackle finish acts as a light diffuser and this snaps via a bayonet fitting into a structure which contains the electronics and a 2 Volt solar cell on the top and above it all is a hook for hanging the unit up. As it stands, the unit can be charged during the day on an inside window sill and be brought inside to work at night giving a good idea of what you can expect from the unit.

The second picture shows the globe removed exposing some of the assembly underneath. The On/Off switch is exposed and the LED pokes through from below. The two screws that fix this plate to the assembly underneath have already been removed.

The third picture shows the plate lifted out exposing the nickel/metal hydride battery and the usual minimal electronics associated with a solar garden light. There is much on the internet explaining in greater detail how these things work. The blue (negative) and red (positive) wires run from the back of the photocell to the small printed circuit board and the constructor may find it helpful to mark the area where the red wires are connected with a red marker. Our duplicate solar cell will be connected in parallel to the on board photocell.

Step 2: Modification (Part 1)

We need a fine wire connection to bring in the power from our external solar cell and connect it in parallel to the solar cell in our garden light. Here I have used telephone connector cable which consists of four single cored wires in a PVC sheath. In this case the sheath is white and this colour is important for aesthetic reasons, (see later.) Here we use two of the four wires namely the blue with white ring and the orange with white ring as our negative and positive connectors respectively--polarity is important. The unwanted wires are snipped back to the sheath and the picture shows how the wanted wires are fed through the hole where the LED protrudes ready to be connected into the circuitry behind.

Step 3: Modification (Part 2)

The picture shows where the existing solar cell was disconnected and the external wires poked into the vacant holes before soldering. I have highlighted these with a white circle. Originally, I was going to leave the internal solar cell disconnected but then realised that this would have sacrificed the ability of the internal solar cell to turn off the circuit in ambient artificial light. After this I reconnected the internal solar cell to these two solder pads and I would now recommend that you simply connect the external solar cell at these points on the soldered side leaving the internal solar cell untouched.

Step 4: Re-assembly

The unit may now be re-assembled in reverse but this time squeezing in the thin connecting wires under the globe bayonet fixing which should produce an effect similar to the picture above. In this case the other end of the wire has been affixed to the 2 Volt external solar cell with the cable length chosen for the particular deployment in the next step. Your own cable length will depend on the application but watch out for the electrical resistance if you try to make this too long with fine wire.

Step 5: Deployment Part 1

The unit may be deployed anywhere that has access to an outside window which receives adequate daylight and an inside requirement for a modest nightlight with the two being connectable by a modest cable run. A child's bedroom nightlight is a prime candidate, an adult bedroom helping older folks not to walk into things, outside sheds and privies--the list is endless. The deployment in our bathroom illustrates the points raised.

The 2 Volt solar cell was affixed in the bottom corner of a double glazed window using 'glue dots'. The first picture shows this from the outside and the second picture from the inside. The third picture shows the 'glue dots' which are sticky in the extreme but it remains to be seen if they make for a permanent solution

Step 6: Deployment Part 2

The picture above shows the business end of the assembly. The light has been hung from a small hook screwed into the underside of the window sill and the cable leads to the solar cell which sits discreetly out of view behind the curtains. The cable is held in place with more glue dots. The aforementioned need for the connecting cable to be white is apparent!--one side of our partnership does not allow just any old thing to be put up.

In short, it works! The unit switches on when it is dark outside or when a light is switched on inside and then off again at dawn. With night vision it is amazing how much light is given off by these units and enables nocturnal night-time visits to the bathroom to be free from incident and loss of that night vision.

Step 7: Some Last Thoughts

There have to be some caveats.

Do not expect a searchlight, however you can see if the unit gives enough light for your purpose by charging it up outside and then deploying it inside to try. Whether this type of light can perform all night, 365 nights per year depends on where in the world you are. Here in the south-west of England our winter days drop down to 8 hours in length and we may have complete cloud cover with drizzle for days on end with correspondingly low energy in what daylight we do get. Recourse to a 'Plan B' may be needed to provide 100% coverage but it surely will not be as simple and cheap to execute as this one.

For a child's nightlight something more junior friendly might be appropriate and there is an example in the picture above of something that would convert. This one was bought a couple of years ago when they were being sold off and do not seem to be available now although you may find them on market stalls, however perusal of a current catalogue shows a 'Solar Stone Owl Light' with two LED eyes and this would make something that a child would truly treasure. They would convert in the same way as shown in the article. There is a vast amount of this sort of material available and it is a constantly changing market.

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