Compact, configurable photographic light surfaces (v2)

The single most important factor affecting the quality of any artistic or commercial photos is lighting. Unfortunately, the world conspires against photographers: point light sources, such as lightbulbs or on-camera flashes, tend to produce harsh and unflattering shadows and undesirable falloff patterns. To add insult to injury, professional lighting equipment that produces diffuse light with good color reproduction tends to be bulky, obscenely expensive, or both.

This page outlines a simple alternative: a compact and portable device that fits inside a drawer when not in use, offers remarkable flexibility, can be built without any exotic tools or skills, and costs around $100. And for once, it does not involve CNC machining!

1. Assembly process

The first step is to find three mirrored sheets of acrylic, dimensions around 25.6 x 25.6 cm, thickness around 3 mm. Local stores that carry advertising supplies should have them in stock. It's also possible to order online from TAP Plastics:

These sheets of plastic need to be populated with several banks of neutral white light-emitting diodes (color reproduction index of around 85). Each bank (A) consists of three LEDs connected in series. For more uniform lighting and lower price, it's possible to go with eight banks of Osram LCWJDSHFQFS5L7N1; for less soldering work, four banks of Cree MX6AWT-A1-0000-000CE5 will offer comparable luminosity.

Within each bank, LEDs are connected together with thick 20 AWG copper wire that doubles as a heat-sink. The banks are attached to the sheet of acrylic with temperature-resistant tape (B). When using 150 mA Osram LEDs, the banks are then connected in parallel pairs, and each pair is terminated with a 6.8 Ω wirewound resistor, rated for at least 5 watt (C). For 300 mA Cree LEDs, each bank should have a separate 6.8 Ω resistor.

Here's an initial test of the LED assembly at about 2% of maximum power:

The construction process described earlier repeats for each of the three mirrored acrylic sheets. It is also possible to add a smaller set of independently-operated, single-color LEDs to each panel; this will permit hues to be added to the resulting light with ease. Possible options:

Next, a sheet of translucent acrylic ("sign white 60%") - around 25 x 25 cm and 3 mm thick (A) - is attached to four strips of mirrored acrylic to form a box. Two of these strips measure 25 x 2.5 cm (B), and two measure 25.6 x 2.5 cm (C):

A four-conductor cable is routed through a drilled hole, and the mirrored panel is attached to the back of the box, with LEDs pointing to the inside. This completes the panel. Here are three panels running at 100% of their output power (3,600 lumens, sinking around 4 A):

With the single-color LEDs turned on in addition to the white ones, each of the panels gains a distinctive color tone:

To make it portable, the whole rig is coupled to a 12 V, 6 A power supply (example). The device can be operated with just a couple of switches rated for at least 5 A at 12 V DC; or can be coupled to several MOSFETs, resistors, and potentiometers to permit the luminosity to be adjusted by hand. (PWM control is more risky than linear regulation, because it may interfere with image capture at high shutter speeds.)

2. Sample results

As a quick comparison, here's a random electronic part photographed in very favorable conditions under a desk lamp:

Here's the same picture lit by two of the assembled light panels positioned on the sides (no light source overhead):

Lastly, this picture uses tinted lighting, mixing blue and red:

Of course, the panels can be moved around or even stacked arbitrarily, so the possibilities are much greater than that.

3. Contact

Questions? Comments? Ping me at lcamtuf@coredump.cx.

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