What is the red light mean on my Stihl 066 - Garden

Here is a copy from an article i was reading

It features a "red light" on the right hand side above the tuning screws which illuminates at a set RPM to assist in tuning the high speed mixture screw, which is great when using the saw out in the field as no tachometer is required to give the saw a quick tune before commencing work. It allows peace of mind knowing that your saw is always tuned correctly and not running a lean mixture which causes damage very quickly. Incorporated with this "red light" system is a rev limiter, so even if the saw is tuned incorrectly it will not allow the saw to over-rev due to a lean out condition and blow up the saw!!