There are 2 important reason that LED must be driven by constant current not by constant voltage
If ambient temperature changes which is inevitable while charging LED, the LED ‘s VF-IF curve shifts towards left.
Under constant voltage driving, the input current will increase wattage and generate more heat which only deteriorate the junction temperature.
Along the length of linear fixture , input volt will drop. Whether or not human eye notices the brightness a,b,c,d
There is inconsistency in brightness while LED receives different current level. Eventually the life time of a, b, c and d is different from one another.
The working habit of previous page still applies here. Probably you have seen tape light with a lot of defect. Main reason can be non constant current input..