Skip to 4:37. A green laser is emitted in the demonstration.
In real life, it's a somewhat majestic bright blue light - clearly visible on an empty wash (Auto Optimal Wash+). I put on an empty wash (I stopped it 5 minutes in because there was nothing to wash) to see if I could spot the sensor in action. The machine didn't disappoint!
About half way into the Auto programme, the machine calculates the turbidity again to determine the soil level. Either that or the machine takes around 45 seconds then to calculate an average reading when it displays 'Detecting Stains'.
There are 4 different levels of soiling the machine can detect:
1) Low soiling - Immediately starts rinsing to save time and energy - Only tends to happen when washing items that need freshening up.
2) Normal soiling - No change to wash time and number of rinses.
3) Heavy soiling - Adds 10 minutes on to the wash time and adds an extra rinse.
4) Very heavy soiling - Adds 30 minutes to the wash time, adds additional detergent and water, increases temperature to around 45⁰C as supposed to 40⁰C, does around 3-5 reheats to maintain the temperature throughout, and adds an extra rinse.
The energy consumption varies significantly. For a lightly soiled delicate load the machine uses 600W of energy. For a very heavily soiled 6-7kg load, it uses 2000W.
Overall, the programme does a good job, but there is a downside. There is no hygiene/60⁰C option which would've been useful for bedding and towels. I'm only saying that because BSH group machines with auto dosing all have a turbidity sensor which is active on pretty much all programmes.