1W Cool and Warm White LEDs

The 1W cool white (6000-6500K) and warm white (3000-3500K) LEDs are driven by 350mA.  The LEDs are mounted on 20mm Aluminum base heat sink plate. The forward voltages after the temperature stabilizes, which is quite warm are 3.18V and 3.04V respectively.  The difference could be due to that the two types are from different vendors.  The plates are hot, probably over 70C (cannot touch for more than 1-2 seconds).  The LEDs seem fairly tolerant of over current; it survives 1A current with the forward voltage at 4.2V.  That's why some of the cheap LED flashlight can get away with direct battery power with any electronics.

The image is taken with 1/2000s exposure with f/8.0; the center of LEDs are saturated.  If we take the measurements at the rims, the cool white LED has RGB composition of .60, .56, .77 and the warm LED .80, .56, .47 .

Here eight 1W cool white LEDs are mounted to a desklamp replacing a 12W fluorescent tube.  A 350mA constant current power supply module drives the 8 LEDs in series.



After some time, I had two LEDs in the lamp failed.  The faulty LED would started blinking; it shut itself off probably due to overheating then recovered after it cooled off.  The forward voltage of the faulty LED becomes much higher: starts off around 3.8V and would increase rather than decrease as it heats up until shutoff; it is still operable at lower current.  To increase the reliability of lamp, I made them into two parallel strings, so they operate at much lower current at the expense of lower brightness (but still plenty of light).