let us go a little bit deeper into driving leds with constant current drivers...
drivers of this kind have a working range, for this driver we see a min. voltage of 17V and a max Voltage of 26V.
leds on the other side have a Voltage drop called Vf* which depends on the current and temperatur.
the influence of the temperatur is about -8mV per 1°C.
If a led starts with a Vf of 2.4V at Room-temp.and heats up 20°C over it,
then the vf is now 2.24V.
for the current we have the following numbers
at 350mA the Vf of a red Leds is about 2.2V, at 700mA about 2.4V.
but there are also some on the market that needs higher voltage, mostly chinese ones.... weak ones or second choice in my êyes.
with all this numbers let as do an example with some weak ones
Vf for each red led is 2.6V at room temp, 10 of them 26V.
we are at the limit of the driver!, but with a little more Temp.(+20°C) we need only 22.4V and the drivers works as he should.
with 9 Leds each at 2.6V we need 23.6V and we are always in the working range of this driver.
*forward Voltage