LEDCard: The Pocketable Ring Light

How many times have you found yourself fumbling about with lighting while trying to get a clear up-close shot of an object? Although smartphones come with pretty nice cameras these days, properly lighting an object and taking impressive macro shots isn’t exactly their strong suit. This is where [MisterHW]’s LEDCard is a very welcome companion. Not only does it provide a credit card sized ring light, it also allows for a molded acrylic lens to be inserted for high-quality macro shots.

The project in its current iteration consists out of a single PCB with rechargeable Li-ion coin cells (LIR2430) and a USB-powered charge controller. After charging the LEDCard (or inserting freshly charged Li-ion coin cells), a single button press will light up the SMD LEDs via the LM3410 LED driver IC. Press the ON button gently (half-press) for medium brightness and fully for full intensity. Finally, pressing the TEST button with the LEDs lit performs a battery level test that turns the LEDs off if the battery is ok. If they stay lit, it’s time to recharge the LEDCard.

As [MisterHW] points out, the LEDCard being compact enough to carry around with you wherever you go makes it suitable as an emergency flashlight as well. It’s also not the final iteration of the design. Future (incremental) improvements include a diffuser for the ring light and more. Even so, in its current state LEDCard is already a proven design.

17 thoughts on “LEDCard: The Pocketable Ring Light

  1. Now, level up by putting a polarizing filter over the LEDs, and another over the lens, rotated 90 degrees to block specular reflection: It entirely blocks the direct reflection from the LEDs, and dramatically reduces glare and hotspots, and increases contrast.

    The camera lens filter is easy as the lens filter. For the LEDs, a phone LCD polarizer works very well.

    I use this setup for my bench inspection camera/microscope. It’s amazing.

      1. Yes, you lose 75% of the light: The polarizer over the LEDs absorbs 50%. Reflection from an average matte target is randomly polarized, so the camera lens filter absorbs half of that.

        My ringlight uses 12 3-watt 300-lumen LEDs, but I run them at a total of 6 watts. After the polarizer I get 150 lumens out, or 1000 lux at my 30-cm working distance. It’s plenty bright.

      1. I’ve described it a few times in these pages before. If you want a tidy paint-by-number guide I’m afraid you’ll have to fill in the blanks yourself — I built it 7 years ago, I didn’t document it for clicks at the time, and even though it’s still a daily driver on my bench, I’m not going to take it apart now.

    1. It still blows my mind that light recycling reflective polarizers used in TFT panel backlights (e.g. https://www.3m.com/3M/en_US/p/d/eebgdar000005/) as well as they do. These would certainly be preferable to plain old polarizer films. As far as I know, they even accept a wider solid angle of scattered light rays as opposed to e.g. polarizing prisms, but that’s where the problems start:
      Can’t stack the polarizer right on top of LEDs without e.g. lenticular film (one-way light transmitting/reflective, CN105334554A, as scattering the light with the LED package and phosphor will reduce efficiency and change the spectrum). And then this light recycling setup also doesn’t do a good job as a diffusor.
      One could switch to a thin flexible PCB and adhere it to a metal, carbon fiber composite or FR4 stiffener, with apertures cut for the components, which would recover the thickness previously lost to the substrate, so a more elaborate light management system can be added on top.
      Don’t think there is an existing market for ultra high efficiency polarized ring lights so far, though.

      1. Jeri Ellsworth did a nice piece on efficient polarizers. If you’re starved for photons or power budget, it’s worth pursuing. Running off wall power, the most you have to worry about is heat dissipation, and isn’t worth the headache of getting the rest of the optical system sorted out.

        But the most important thing is the polarizer must be the very last thing in the optical path as the light leaves the ringlight. *Anything* in the path after that point generally mucks up the polarization: Plastic rotates the polarization randomly enough to ruin the blackout effect. Even high-quality glass has enough imperfections to be visible. Even dust on the front scatters enough to reduce the contrast. It’s amazingly sensitive.

        1. One may be able to sacrifice a bit of the extinction ratio for convenience though – e.g. Scotch tape is famously birefringent(1) but doesn’t interfere when taped down parallel or perpendicular to the linear polarization.

          Btw. – unlike the “30-cm working distance” scenario, 3-5 cm front focal length turns the ring light in a dark field illuminator of sorts, which can help suppress specular reflections otherwise subject to polarization-dependent suppression, which is an “ok” compromise at least in some circumstances.

          [1] https://www.nature.com/articles/pj201252 (see Fig.1; I think Scotch tape has the fast axis perpendicular to the strip, anecdotally reported as Δn = 0.0077 ± 0.0003)

  2. I think it would take two steady hands, one to hold the phone/camera and the other to hold the ring card at the proper distance to focus its lens, all while viewing the subject through the display.

    1. Place the LEDs and any polarising filters in a plastic add-on phone case. Leads go to copper (or aluminium) plates.
      Now your PCB needs only have the power supply, making it much smaller. Push the PCB against the back of the phone case with one hand, look at the screen to aim, tap shutter button with other hand.

  3. BTW clip on ring lights showed up at Dollar Tree, I picked one up to screw with for next time I’m doing macro shots, not expecting much, but might be better than nothing. Also check out your local liquidation stores for sets of clip on “As seen on TV” sets of macro lenses going cheap.

  4. Since front camera’s on smartphone have become a lot better, they might feature a special mode where the screen would be set to all white instead of showing the picture of the camera. That would work as a simple ring light i guess. Problem is you won’t see anymore how the lens is aimed (although if you got all the apple gear you can use your apple watch for that).

    1. As a compromise, you could use a high brightness low contrast viewfinder image on the front screen as illuminator for front camera images. So you have an impression of the image and still light.

    2. “they might feature a special mode where the screen would be set to all white instead of showing the picture of the camera”

      That’s already a feature of the stock Android camera app.

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