According to the datasheet you can't dim it to 0% when fed with PWM. Even when supplying a DC voltage it doesn't go down to absolute 0.
I think, that you make a design w/o math. Data sheet for driver says: 43.2 ~ 52.8VEven it's adjustable, I don't believe you can drop it to 8 x 3.5 = 28 V w/o consequences.My guess is, when you request (by pwm) to drop current below 25% driver become unstable, as it moved out of "normal" operation zone.This confirmed, why it's working with 10 leds, because 10 x 3.5 = 35 VSolution: edited:1) change driver for .... ooopss, eln-60-27 (good for 8 leds maximum) you can split diodes in a group of 4 leds, and use 2 drivers eln-60-122) add more leds in series, up to 52.8 / 3.5 = 15, minimum 43.2 / 2.8 = 15, again 15, now we know how they calculate their data sheet May be 10 would be o'k, but as you can see, there is no warranty.
Math is pretty simple:page 8 in documents for leds, shows charts V-A for different color leds.The range for blue led V = 2.8 ( I = 0 ) and V = 3.5 ( I = 1000 ma ).Multiplying this digits by number of leds you plan to connect in series, you will getminimum and maximum necessary voltage from power supply(driver).Using this info you can check in data-sheet for driver witch model best fits.
I've just read in a fish tank forum how they were able to solve the flash by turning off the power supply before the LEDs are dimmed to "0". I'll give this a try and check back in. Thanks for the help guys.