LED Light Design thermal issues

vivitern

I traced the below circuit from one of the WiFi based LED downlight available in the market. This circuit works at 17V (Regulated Supply) and takes 450mA max. current if fully bright. Now I am going to replace the white LEDs with the one I will purchase from the market, but the problem is with every lot the forward voltage will change with their voltage group. I plan to add NTCDS serials Thermistors, datasheet:  http://www.kynix.com/uploadfiles/pdf8798/NTCDS3HG103GC3NB.pdf

Schematic :- 

Specs of LEDs which I will be using :-

• If (Forward Current) : 60mA(Typical) and 90mA (Max)

Forward Voltage Group :-

Graph :-

LED PCB :-

Questions :-

• What can be the thermal issues with New LEDs I will be using?

• Also How to deal with different voltage groups LEDs in the circuit?
  Because it's difficult to change the circuit every time for every
  lot.

• The forward voltage decreases with increase in temperature, so will
  hog more current? How to deal with that?

• Do I need any kind of limiting resistor with the LEDs string?

Priknr1

I think your are deeper in to electronic knowledge than 99% of the people on here.
This kind of question is more probably answered on a electronics forum like:
https://www.circuitsonline.net/