diff --git a/fhem/CHANGED b/fhem/CHANGED
index 102dbbd86..7b64d42de 100644
--- a/fhem/CHANGED
+++ b/fhem/CHANGED
@@ -1,5 +1,6 @@
 # Add changes at the top of the list. Keep it in ASCII, and 80-char wide.
 # Do not insert empty lines here, update check depends on it.
+  - bugfix:  51_I2C_TSL2561: correct lux calculation floatArithmetics case
   - feature: YAMAHA_AVR: add pointer to main zone in Internals for zone defs
   - change:  YAMAHA_AVR: DSP based models use command queue of main zone
              to execute commands for zone definitions 
diff --git a/fhem/FHEM/51_I2C_TSL2561.pm b/fhem/FHEM/51_I2C_TSL2561.pm
index b684c40fa..336552d55 100644
--- a/fhem/FHEM/51_I2C_TSL2561.pm
+++ b/fhem/FHEM/51_I2C_TSL2561.pm
@@ -1196,7 +1196,7 @@ sub I2C_TSL2561_CalculateLux($) {
     if ($hash->{tsl2561Package} == TSL2561_PACKAGE_CS) {
       #  CS package
       if ($ratio <= 0.52) {
-        $lux = 0.0315*$channel0 - 0.0593*$channel1*pow($ratio, 1.4);
+        $lux = 0.0315*$channel0 - 0.0593*$channel0*pow($ratio, 1.4);
       } elsif ($ratio <= 0.65) {
         $lux = 0.0229*$channel0 - 0.0291*$channel1;
       } elsif ($ratio <= 0.80) {
@@ -1209,7 +1209,7 @@ sub I2C_TSL2561_CalculateLux($) {
     } else {
       #  T, FN and CL package
       if ($ratio <= 0.50) {
-        $lux = 0.0304*$channel0 - 0.062*$channel1*pow($ratio, 1.4);
+        $lux = 0.0304*$channel0 - 0.062*$channel0*pow($ratio, 1.4);
       } elsif ($ratio <= 0.61) {
         $lux = 0.0224*$channel0 - 0.031*$channel1;
       } elsif ($ratio <= 0.80) {