Electronic markers for finding your way in the dark.
BUILD TIME: A few hours (each)
DIFFICULTY RATING: Intermediate
Part hack-athon, part scratch build, we present several alternatives to chemical light sticks for marking paths, hazards, or items in temporary situations.
Have you ever been camping and tripped headlong over your tent pegs or guy ropes, or led a group of people through the dark like a school group on an astronomy night? Have you had someone (or yourself) trip over your camera tripod set up at a lookout or foreshore for a long-exposure night shot? There are a variety of situations where there is a need to mark an item or pathway for people who may not be familiar with the safe route by memory.
The traditional solution has been chemical light sticks. These do have their advantages but in some situations, we can come up with something better. Chemical light sticks are self-contained, so there is no need to carry batteries or worry about the batteries having gone flat while the product has been on the shelf. They are reasonably bright and come in a range of colours that can be used to colour code things, like green for a safe path and red for hazards like steps or guy ropes.
However, they are single-use, and a new one is needed every night. That’s ok for a single outing like the school stargazing night, but not great for a two-week camping trip. They also generate a waste problem, which presents ethical issues for many people. The chemicals in them are not exceedingly toxic, but some of them are not biodegradable or environmentally compatible, either; and that’s without the plastic case considered! They also have a shelf-life, after which results are not guaranteed.
Instead, we have pursued a few different options for reusable versions. To suit different people and different situations, we have come up with a design that modifies a commercially-available battery-operated LED light stick; another which is USB-powered and runs from a power bank; another which is fully self-contained and recharges from USB; and another which takes a removable Lithium-ion battery and, therefore, has less circuitry inside. All of them have the potential to be customised, both in colour, brightness, and shape in the cases of the scratch-built versions.
There is quite a lot of text dedicated to explaining our thinking here. There isn't very much to this project electronically. While this may be a bit boring for some, its point is to help you understand the thinking if you want to make changes. It's ok if you want to do exactly what we did, but if you wonder why or want to do anything different, knowing the process or reasons for decisions can help you avoid mistakes or missing things out. We also discovered a lot about the details of how LEDs throw their light!
There are several commercial options already available, and these will suit some people. However, they have caveats. Few are particularly bright, with many not even as bright as a traditional chemical light stick. In most cases, they also use a set of three alkaline button batteries, like LR44 or smaller. These end up being quite expensive to replace in any quantity unless super-cheap and consequently very poor quality online bulk lots are used. The exception we have found so far is a Coleman branded product available at Bunnings, which runs on a single AAA battery. Others have some cool features, like the ground stake option we found at everythingglows.com.au.
They’re very cheap, so you would probably dispose of them rather than replace the batteries, which takes us back to the waste and sustainability issue. We did like the format, and it would suit certain situations. However, it is not bright from a distance, and the good functionality of the ground stake with its long, thin light source does not, in our consideration, offset the disposable nature. It’s still a cool product!
MODIFYING A COMMERCIAL PRODUCT
The Coleman version is the product we decided to modify. It still uses disposable batteries, but it has some advantages. You can use it for longer than a standard lightstick off a single battery. It has a flashing mode, and a torch as well. It is possible to recycle AAA batteries if you can find a collection point, too, which helps form the waste-management point of view.
As-is, the product is available in red, green, yellow, and blue light. The torch section is the same white light for all. The LEDs fitted to these products tend to cast a bright spot on the end and a bright ring around the bottom, but the rest of the surface seems to miss much of the light. This is actually somewhat typical of the LEDs used. The lenses on the high-brightness water-clear LEDs often result in this pattern with little recourse to any manufacturers to do anything about it.
Our project involved three goals: Firstly, to increase the brightness on one example as a track marker, visible from a distance. Secondly, to alter one example to be quite dim, so as to serve as a marker for a camera tripod, visible up close but not from far away, and not throwing light that may leak into the shot. Thirdly, to alter the LED in the torch section to provide night vision-friendly red light.
The entire electronic section of the torch is removable for battery replacement. Doing so reveals quite a complex circuit board. It has an entire LED power supply onboard, which steps up the 1.5V from the AAA battery to a voltage high enough to drive the forward voltage of the LEDs. We measured 2.99V for the coloured LED, which could not be disconnected without desoldering. The torch LED is on its own circuit board with spring contacts. It was measured at 4.08V at the contacts without the LED connected, and 2.89V with the LED assembly in contact, running at 21mA.
This told us that we could comfortably use standard high-brightness LEDs in the 2V to 3V, 20mA to 30mA range, which made the low-brightness versions easy. It also made the high-brightness versions easier, but still eliminated the use of some extreme high-brightness through-hole LEDs, which can draw up to 100mA in some cases, like parts of the Cree range.
Besides brightness, the main factor in LED choice was light dispersion. The original LEDs threw quite a bright ring around the lower quarter or so of the white plastic case, then a bright spot at the top of the tube. The rest was appreciably darker. All LEDs have a light dispersion pattern with brighter and darker regions even within the stated viewing angle, but it is more noticeable in some than others. The viewing angle itself also plays into this. 5mm resin-cased T1¾ LEDs typically have viewing angles from 10° to 30°. However, always check the datasheets. This figure can be the angular distance between a line straight out from the centre of the LED, and the point where the light level reaches 50% of the peak brightness. However, we have found some manufacturers and some retailers quote the figure meaning the total angular distance between the 50% brightness point on one side, and the same on the other. You could have two LEDs, one quoted as 15° and another quoted as 30°, with dispersion patterns that look exactly the same.
We did explore options for altering that pattern. For example, diffused LEDs have a much more consistent light pattern, so we tried sanding the outsides of the case, and we tried painting with a thin, fine coat of white spray paint. Both options produced a difference but neither was really satisfactory. Of course, the chances of success were never terribly high, but it was worth a try. Diffused LEDs have a case that is made of translucent resin rather than clear. Dispersion is a process that occurs constantly along the light path from the LED die to the edge of the case, rather than on the outside as it is with sanding or painting. We also tried filing flat the top of an LED case, but this also produced a result that was, while a greater difference than the other attempts, even less satisfactory: The difference was bigger, but the light pattern was vastly wrong.
In the end, we decided not to modify the LEDs. Instead, we bought a few each of several different varieties and tested them inside the case of the commercial light stick, looking for which one gave the best pattern of light. The ideal situation is to have light spread as far up the sides as possible, so there is not one intense band and a lot of unused space.
The commercial light sticks are available in red, green, blue, and yellow. Replacing the stock LEDs with our own opened up some possibilities, but the end-use purpose of the light sticks really dictated the colour of LED we chose. Few people have not at least seen a film scene where some military force is using red light at night. Quite often, this is a navy ship at battle stations, or a headquarters unit directing operations.
There is a reason for this, and it is the same reason red light is used in astronomical observatories and photographic darkrooms, for those who remember what those are. The human eye takes around seven minutes to adjust from red light to darkness, while from white light, it takes around forty minutes. Studies and sources vary on the times, but the point does not change. In the military situation, people need to function if power fails due to battle damage, while in observatories and darkrooms, the lights need to be turned off and operations take place in darkness. Red light has another advantage in that it is less noticeable from peripheral vision.
By contrast, green light is very noticeable. The human eye is around ten times as sensitive to green light as to red light. It is very noticeable to the brain, as well. Blue light is not far behind on these fronts. Green light is generally not noticeable to animals at night, and so is a popular choice for wildlife observation. Blue light bounces less off smoke and vapour clouds. Light sticks will not be used for these tasks, but the principles may be a factor. For example, the green markers might be good to light a path if you are leading people on an observation of nocturnal wildlife: They won’t disturb the animals as much.
As an aside, military ground forces now tend to use green light at night. While more noticeable to the unaided eye than the traditional red torch, the reason is the prevalence of cheap ex-Soviet night vision devices among even unsophisticated and irregular forces, and these work on Infrared light, with a significant spill into the red part of the spectrum. Red torches are to these devices what a lighthouse is to a ship at sea. There have been other science-driven changes too, and it is less common to see red light in military applications. It does, however, remain in the civilian applications we listed, as the needs vary.
The upshot of all this is that you have to consider the end use of your light stick before choosing a colour. For the light sticks we converted to be used for marking tripod legs during night photography, we chose red, and at a lower than stock brightness as well. For the light sticks we modified for leading a group of school-aged youth group kids through the bush for an astronomy night, we chose green for the path markers and blue for trip hazard markers, as both are visible from further away. We used red closer to the observation area for eye adaption. You may wish to use another colour, even white, depending on your needs. We really wanted a yellow-green light like the chemical light sticks, but there are few LEDs made in this colour.
MODIFYING THE STOCK ELECTRONICS
With the LEDs decided, we set about removing the old ones. When it comes to the red photography lightsticks, we wanted to alter the white torch end as well. A brighter red light here would provide a useful torch that still preserved night vision. A vacuum desoldering station will really make life a lot easier with this task.
From the front of the board, the spring contacts have to be desoldered. A hot iron helps, otherwise, the nearby plastic melts as the contact slowly heats up, sinking the heat away from the joint. With these cleanly desoldered, they can be gently prized out from the back. This will release the circuit board from the plastic frame, and allow desoldering of the LED. After inserting your LED of choice, just reverse the process.
Getting the light stick LED out is much easier than getting the new one in. The legs join to the very end of the PCB. Even without a vacuum desoldering tool, this one is fairly easy. Be sure to clean the pads as much as possible, however, or getting the replacement LED in will be even harder. Desoldering complete, slide off the white cap and the LED can be pulled out with a pair of pliers: The legs will pull through the assembly and follow.
Getting the new LED in takes patience. First, the legs have to be bent at 90°, in the right direction so that they will feed through the space and come out at the top with the correct polarity. Once through the hole in the front of the case, turn it over and use tweezers or a probe to manipulate the legs toward the holes in the PCB. Keep a bit of pressure on while you do, and keep it gentle until the legs are through the holes and slightly protruding above the surface of the PCB. Then, you can turn it back over and pull on each side a little at a time alternately until the LED is seated on the front of the assembly, and solder the legs down.
After this, you can gently reassemble the various components. Make sure the different pieces of the torch end are oriented correctly, and be careful of raised solder joints or protruding legs at the light stick end as it is installed. Turn it on and test it, to hopefully see a much brighter or dimmer light than the stock one. We made three dim red ones to mark the legs of a tripod, and two much brighter red ones as the leading two marks at the end of the track into the astronomy observation area for the kids. The dim photography ones would be used for the final stretch. We have also made a group of green and blue ones, but all of these are brighter than stock. They also mostly have modified torch LEDs of whatever colour the light stick is. Some are the brightest we could find, others are low-intensity for preserving night sight.
For our own scratch-built versions, we have three options, but all are variations of the same core design. The light stick end is the same in each case. The differences are in the power supply. One has a USB plug protruding out of it for attaching to a USB power bank. Another has a 5V DC-DC converter and a removable 14500-sized lithium battery which sits in a AA battery holder and can be recharged externally with the appropriate charger. You could also carry spare charged batteries but we don’t see a major need.
|1 x USB A Plug||USB||PP0790||-||ADA1827|
|1 x USB C Socket OR USB C Socket Breakout||LiPo||PS0930||P1315||ADA4090|
|1 x 5V DC-DC Converter Module||LiPo/14500||XC4512||Z6366||-|
|1 x 3.7V Lithium USB Charger Module||LiPo||XC4502||Z6388||ADA1904|
|1 x 3.3V DC-DC Converter Module, Optional*||LiPo/14500/USB||From LEDsales, part 3V3_CP_REG|
|1 x 3.7V 300-400mAh Lithium Battery||LiPo||-||-||PAKR-A0317|
|1 x Micro Slide Switch #||LiPo/14500||From LEDsales, part DPDT_SLIDE||-|
|1 x 14500 Lithium Battery||14500||SB2300||S4979||-|
|1 x AA Battery Holder||14500||PH9203||S5026||-|
|1 x Resistor to match specific LEDs||LiPo/14500/SUB||-||-||-|
|1 x LED Of Choice and Resistor To Match|
Additional Parts: See text for details of LED Choices for each version, and the modified commercial options.
* This can replace the 5V DC-DC Converter for LEDs with a forward voltage of 3V or less.
The final version has an internal lithium battery, a charging module, and a DC-DC converter module for a stable 5V output.
All three power options have a common light element: A conical diffuser above a very shallow conical holder for a 5mm LED. We chose a cone to make best use of the light spread pattern from the LED, after experimenting with a variety of other shapes. We tried parabolas, cones, and truncated cones, all of different diameters and slopes. We even tried plain cylinders, but the cone proved the most effective. While we have provided the 3D print files, the cone is a separate print because you may need to change it to suit your LED. We found different heights, giving a different angle to the sides for the same base diameter, give differing results with different LEDs because of their light distribution patterns.
The cone mounts on a base which has a reverse conical surface for the LED to mount in. This reverse cone can be covered in foil or silver paint to help reflect some of that very intense, almost horizontal, band of light that most high-brightness LEDs emit. It will never be a mirror, but it helps use some of this light. You can choose whether or not to bother with this.
3D Printed Parts Required: USB Housing, Diffuser Base, and a diffuser of choice.
Below this section is where things differ. One version has the housing for a USB plug mounted here, with the electronics being no more than an LED and its resistor.
The resistor can be calculated precisely if you want maximum brightness, from the forward voltage and current specifications for your specific LED. However, in most cases the voltage or current needs to reduce an appreciable amount for the brightness to visibly differ. So, you can generally get away with the 150Ω resistor often used for LEDs on 5V. After soldering the appropriate resistor for the chosen LED to one of its legs, the LED can be mounted in the USB plug. Solder the leads onto the correct terminals! Don’t be like us and solder from the back of the connector while looking at a diagram showing the front, then wonder why you get no light. The photograph is the correct wiring.
After we corrected this, we used hot melt glue to flood the electrical connections and isolate them from the metal USB plug body. After that, the assembly is slid into the 3D-printed housing and glued into place, before the dispersion element base is glued on top. Now, you can slide on a disperser of choice, and install the USB plug into a redundant power bank of the sort often provided as promotional items or common before phones became so thirsty.
14500 Battery Version
3D Printed Parts Required: 14500 Housing, 14500 Cover, Diffuser Base, and a diffuser of choice.
This version has a bit more to fit in it. In addition to the AA-sized 14500 lithium battery, a 3.7V to 5V converter needs to fit as well. It may seem inefficient to convert up to 5V then reduce with a resistor for the LED. However, the LED needs a resistor for current-limiting no matter what, and using the converter not only gives a very stable voltage for the life of the battery, it also stops the battery being discharged to the point of self-damage. We used a 3.3V DC-DC converter from LEDsales for our original build, which can step up or down using a charge pump configuration. It was great, but some high-brightness LEDs have a forward voltage of 3.5V, so we went with the 5V option.
The step-up converter used is intended for Arduino projects and has a USB socket on one end. This is removed, first by cutting through the mounting tabs and connecting tabs with side cutters. Not doing so can result in damage to the pads and tracks of the PCB, as the solder often extends underneath the frame and desoldering may not be complete when you pull off the socket. We thought we had desoldered our first one, then levered off the plug to find it took several PCB tracks with it. Once that job is done, you can trim off some of the front of the PCB if you wish. Some of the section under the USB socket is there only for the support of the socket.
The converter gets glued into the case above a single AA-size battery holder. We chose this instead of sourcing battery terminals and making our own integrated holder, because terminals are not the easiest thing to come by over the retail counter. You may find them online but the converter, battery, and holder are all on-the-shelf items at the major electronic parts retailers. We used a tiny slide switch from LEDsales but Jaycar, Altronics, and some online retailers have small slide switches too, just not this small.
Solder the battery wires to their respective terminals on the converter, but break out the positive wire to the switch before continuing to the converter. Solder the appropriate resistor to the LED, then attach light-duty hookup wire to the legs. Heat shrink or otherwise insulate the bare metal. Glue the base into the housing, and solder the LED wires to the output of the converter. Glue the converter, battery holder and the switch into their places, and the LED into the disperser base. The base is a separate part, common to the other designs.
The whole assembly is protected by a sliding cover. This doesn’t have a latch, as we found friction was enough. Because of printer tolerances, you may need to file the channels on your print, or yours may be too loose.
Internal LiPo Version
3D Printed Parts: LiPo Case, Diffuser Base, LiPo Lid, Diffuser of Choice
The final design utilises an internal Lithium Polymer battery, charger, and DC-DC converter. The original intention was to have these set up as a bank with a charging station. However, finding connectors which suited that and were easy to use, effectively ‘foolproof’, was not easy. Many similar arrangements, such as those to charge fleets of two-way radios, or workplace torches, often use custom cradles with spring-loaded contacts or magnetic locks. Neither was as easy to implement as it should have been. Accordingly, our design is charged from a USB-C socket, meaning a phone charger can be used. This can be a mains plugpack, in-car charger, or power bank.
Additionally, the USB-C socket is offset, so you could add key tabs to the base, design a cradle to take them, and mount USB-C plugs in the base. We will probably do exactly this when time allows, with a custom PCB to both mount and support the plugs, and distribute power to them. For now, however, we’re just charging these with any of the many phone chargers we have lying around.
As with the other designs, the base for the diffuser elements is separate. The housing is a rectangle with space for a 400mAh LiPo battery, battery charging module, DC-DC converter module, and a slide switch. A base is glued into this as a cover, and this has a cut-out for the USB socket, which is also glued in. The USB-C socket deserves special mention. It has more pins than many of us are used to for USB: There are nine in total on each side of the internal tab. They are mirrored so that the plug can go in either way and the connections are still correct. Only two are for power, and top and bottom contacts of the tab come to a common pin for each, so eighteen contacts turn into nine pins.
Desolder the USB plug, the same as for the 14500 version. Trim the board, to leave room for the switch. This version uses two positions of the switch: The battery goes to the common, with one position going to the DC-DC converter (the ‘On’ position) and the other going to the charger module (the ‘Charge’ position).
The grounds for the DC-DC module, charger, and battery are all common. The switch can cope with the connections, but the less wiring in the small space, the better. We laid the charger horizontally across the battery and the cut-down DC-DC module vertically on top of that. We used hot melt glue to both join and insulate. While LiPo batteries get hot during charging, if they get hot enough to melt hot melt glue, the PLA printed housing will soften, too.
With the connections wired on the bench, we can add the resistor and LED to the DC-DC converter, and glue the diffuser base to the LED. This way, everything can be slid inside the housing, and the diffuser base glued in after. This minimises the amount of wire involved, and the same applies to the USB-C Socket. That can glue into its place when the other components are home, and then the lid can be lightly glued on.
Now all that is needed is to plug in a USB-C cable to charge it. By having the charger facing outward with the DC-DC module under it, we can see the charging indicator LEDs through the printed walls. That is, assuming you printed in white or natural, as we did. If you use black, or a solid colour, this may not be the case. As with the others, you can attach a diffuser of choice.
WHY A CONE?
We chose a cone as the shape for the diffuser element after trying quite a few different shapes. Regular chemical light sticks are typically straight-sided for smaller sizes, and a slight taper for larger sizes. However, the light is emitted by a chemical reaction which occurs along the whole length of the light stick. The shape of the tube is based on manufacturing and end-use practicalities.
With our light, the shape is dictated by the need to scatter the light from a point source with a radiation angle. While a straight cylinder or slightly tapered truncated cone like the 150mm chemical light sticks does work, it is inefficient. There is minimal light along the tube, dark spots in places, and a very bright point on the top face or near the top. The idea of the cone is that the light radiating at a somewhat narrow angle from the LED will strike the cone along its length, and even at the top, the light is scattered for side-on visibility.
There is no reason to use a cone besides this optimisation. You could experiment with any shape you like, from a sphere, to a pyramid, to a double helix. We made a few other shapes just for fun. Having said that, think of your end use:
By diffusing the light from a longer surface, you increase the visibility in some conditions. While in a broad open space, the brightest light is the easiest to see, the same cannot be said through foliage or any other barrier. A long light has more chance of being seen and not hidden from a certain angle by something as small as a single leaf.
WHY A 5MM LED?
We also experimented with 5050 surface mount LEDs, along with Superflux-style through-hole square LEDs. Both of these have wide viewing angles. However, they resulted in a bright band toward the bottom of the dispersion element (the cone) and had little brightness going on further up.
We hypothesise that this is due to the light’s relatively even distribution across this wide arc, meaning that only a small amount of the radiant light interacts with the majority of the cone. Most of the light interacts with the closest parts of the cone. If you want to use spheres for your dispersion element, 5050 LEDs may work very well.
There are also choices to be made here. You can use white or natural filament for the diffuser and a coloured LED, which most of ours use. However, you can use a white LED and any coloured filament you like, as long as it transmits some light. This was particularly useful when we wanted a bright ‘fluorescent’ coloured light. We couldn’t find a ‘chartreuse’ or ‘safety vest’ yellow, but we found something close in Sunlu’s ‘Noctilucent Yellow’. This is a very vibrant yellow with a faint green tinge, and a tiny amount of phosphorescence. So faint that at first, we didn’t even realise there was any. However, in total darkness after a bright light, the glow is visible. We are currently looking for an orange of the same ‘fluoro’ colour that some safety vests and shirts are made from.
The parts presented can all be used as-is, or as a basis to modify for your own use. For example, you may wish to enlarge the 14500 build to take an 18650. One change we would make ourselves if we were to build more of the LiPo version is to use a USB-C breakout instead of a bare socket. They are much easier to wire and a few pins snapped off our sockets.
The housings can all be printed with as many shells, as much infill, in whatever layer thickness you like. We used three shells, 20% infill (not that there was much of it) and a 0.3mm layer thickness, printed in PLA.
However, the diffusers and diffuser base are different. The diffuser base should be printed in a 0.1mm layer height or less if you want to paint or foil it as a reflector. This will mean a much smoother default surface, which will sand easily. The shell count and infill are still up to you. We used three shells and 20% infill.
The diffusers are the hardest part. We found that the best way is to have a solid rather than hollow model, and print with one shell, 0% infill, and no solid bottom layers. This gave us the smoothest and thinnest prints. Our printer did not like printing such narrow models in vase/spiral mode. The other advantage of printing this way is that you can also print with two shells. This is a stronger print with less light transmission as the trade-off, but it might suit some filaments and applications ok. We have several diffusers for download. One is a straight tube, one a tall cone, one short, and one in the middle. These will each give differing performance with different LEDs, so you may have to try them to find out which works best for you.
Additionally, we have one last part not discussed elsewhere. There is a part called a ‘Balloon Base’, which is just that: It is designed to go over the Diffuser Base, and has to be glued on for air sealing. Then, a balloon is partly or fully inflated and placed over the base, which is wide enough to elastic-seal the balloon. This gives a round shape visible from many angles even through foliage which may hide a narrow light. It is designed for use with wide-angle or 5050 LEDs. We were going to print a sphere, but they don’t cope well with low shell counts and 0% infill!
Finally, we included some items not part of the builds themselves: These are bases that accept each light style, and allow them to be turned into a ground stake with the addition of some strong wire like a coat hanger. We also have in mind using hook and loop (Velcro) cable ties to attach these to guy ropes or tree branches where necessary.
REAL WORLD TESTING
No project is complete without an in-situ test. Luckily, it is the perfect time of year for fireflies where DIYODE is based. Accordingly, we took all of the light stick options to the youth group that one of the staff is involved in. With the facility hosting the group having a patch of the right kind of bushland nearby, with built paths and dirt tracks through it, we had a perfect test bed. Green lights showed the paths to take, red was used for trip hazards like step edges or tree roots, and blue was used for junctions or points of interest. Then, the teenagers were briefed on the situation, with the colours explained repeatedly.
The walk was a success, with no injuries or lost teenagers reported. More importantly, no paperwork was generated besides the pre-event hazard assessment and control plan. There are other problems taking a bunch of teenagers into a dark place, so we made sure leaders were spread around, but none were called on for navigational help or to deal with any illicit substances. The first part of that, and the feedback from the teenagers, suggests the lights were a success.
We will find out later when we take them for an astronomy night further away from the city lights and along a longer bush path.61a0a04dc672e0020f89a351