I have a lamp that has LED driver producing 35 V (actually lamp driver says 15 - 25 V, but I've measured 35 V). On the lamp I have 7 LEDs (originally 5 + 2 I've added) with heatsinks that have burned and replaced a couple of times now. All LEDs are connected in sequence.

LEDs specs:

• LED Emitter: 3W
• Output Lumens: 180-210 Lumens
• DC Forward Voltage (VF) : 3.6-3.8Vdc
• DC Forward Current (IF) : 700mA
• Color Temp: 6000~6500K (white)
• Beam Angle: 120 degrees
• LifeSpan Time : > 50,000 hours

So I've figured out:

$$R=\frac{V_{Driver}-V_{LED} \times 7}{I_{LED}} = \frac{35\ V-3.7\ V \times 7}{0.7\ A} = 13\ \Omega\ $$

which is nothing. At the same time my LEDs are burned down within a month.
What am I doing wrong?