Need help with break beam sensors for an art installation
The optical link part of your break-beam project should use a turn-key solution so that attention can be diverted to coding.
Fortunately, the remote-control system we use for TV/Audio appliances is suited to your application:

works in daylight
copes well with varying environment.
has range greater than 2 meters.
uses &quot;safe&quot; infra-red light from a LED
the LED light source can be driven directly from a microcontroller I/O port.
the IR-remote light detector provides a digital signal to a microcontroller I/O port input pin.

Infrared remote receiver (pins are OUT, +Vcc, GND):

An infra-red LED can be driven with a logic signal (with a series-resistor) directly from a microcontroller I/O port.
This signalling system requires that LED be driven ON/OFF with a 40kHz signal. The IR-remote data sheet should show timing requirements. Requiring six separate beams complicates the problem, but encoding each channel with six unique code sequences provides a potential solution.
Since transmitted light from six LEDs can scatter from an unknown and changing environment, expect that each of six IR-remote receivers must discriminate between transmitted code sequences. A blocked beam would result in a code not being received.
The microcontroller would look for missing code sequences from six receivers.
These IR-remote receivers are very sensitive, and respond well to reflected light. Confining the LED transmitted beam divergence would help considerably to reduce the reflected-light problem. Many LEDs are encased in plastic with lens with small beam divergence, some to +/- 8 degrees. A tube shroud may help confine transmitted beam even more.
Most IR-remote receivers are designed to accept light from wide angles. You might be able to confine the received beam with a shrouding tube as well.
Your microcontroller will be kept busy looking for six received codes from each IR-remote receiver, but should be able to cope if coded efficiently. It might be wise to enable pull-up resistors to +Vdd on IR-remote output pins.
You might try a simple version first, with all six LEDs transmitting the six unique codes one after another, repeating continuously:



simulate this circuit &ndash; Schematic created using CircuitLab