The light sensor will be able to cope better than the touch sensoras a counter, even if the speed of the  conveyor is increased.

Sensors

Sensors are devices that are used to measure or detect a specific response or movement and to convert this information into a signal that can be interpreted and processed by an observer, another instrument or a computer. A sensor can collect data and convert it by many means and methods. Sensors are actually transducers, devices that help to convert energy from one form into another.

There are many types of sensors that do not depend on electronics means to convert and interpret data. The thermometer is one such example. The expanding mercury in the thermometer will detect thermal energy. The kinetic energy in the mercury atoms will cause the mercury in the thermometer to expand or contract accordingly. The mercury level will rise up or down to indicate the temperature.

Modern day sensors can be found everywhere around us. Our cars have fuel gauges to detect petrol levels, thermostats to monitor engine temperatures, speedometers to show the speed, reverse sensors and car alarms. Sensors are also used to detect light, touch, temperature, proximity and are used in thousands of applications.
 

The hypothesis that the light sensor will be more effective even with a faster conveyor belt is proven to be correct. The light sensor did not require physical contact with the sensor whereas the touch sensor required physical contact for detection. This resulted in greater friction between the boxes and the sensor and as the speed of the conveyor increased, causing the boxes end up being displaced.

Sensors can be found everywhere around us. When we turn on the air conditioner, the thermostat detects and regulates the temperature in the room. Street lights also have a light sensor where the lights automatically switch on at night and automatically switch off in the mornings. There are also many sensors within a car which help to detect engine temperature, unclosed doors and fuel levels.
 

Try to repeat the experiment by using other sensors like a proximity sensor.

The experiment can also be done by increasing or reducing the space between the boxes.