The Minimalist Light Meter is a project I've been working on for a while and I'm pretty excited to have finished. It's an ambient reflective light meter designed to be as simple and inexpensive to make as possible. It's completely open source. That is, the code, schematics and case design are all available under a GPL3 license. It's quite easy to make one yourself, if you are comfortable with soldering small surface mount components.
There are a few key design decisions that justify the ‘minimalist’ moniker:
The PCB is of the standard two-layer 1.6mm type. Components are only mounted on one side. PCBs like this can be manufactured at very low cost even in small quantities.
Touch-senstive pads are used rather than push buttons, reducing the component count.
The bottom side of the PCB is used as the front panel, making it possible to design the case as a single 3D-printed part.
LEDs are used to display readings rather than a display panel. This slightly reduces cost and significantly simplifies assembly and part sourcing.
Here's a photo of the top side of the board showing the components: