DIY 10-CREE LED Light

[jamesneo]

Hi,

My 2x 36WPL light (light now is slightly yellowish already) is due to change after Chinese New Year. I did some research and read up on items to purchase on the website as well as some of the information here. Here are some items that i want to purchase:
1) LED Driver– Waterproof 1A 30W Power Constant Current Source LED Driver (100~240V) x 1piece

2) Cree XR-E Q5 Emitter on Premium Star (228LM at 1A) x 08 pieces

What do you think? Total cost is around $80+ to replace the 2x36WPL tube (Assuming i spaced out the 4 LEDs at 12cm apart to replace 1 x 36W PL) .
Is 08 CREE LEDs enough or should i use 10??
Is the LED driver rating suitable?
I am not planning to use any 10W resistor. Is that alright?

Thanks and Happy Lunar New Year. Huat !!!

[iewnuj]

You might want to get a 700ma driver instead. Not worth driving the leds to their limits, since its not going to be much brighter and there will be less heat issues too.

[li_gangyi]

If there is enough demand, I can make PCBs that'll turn normal power supplies into constant current sources. PM me with your specific design (input voltage, amount of LEDs and required current) requirements and I'll churn them out. Great way to turn those useless laptop adapters into something useful xD.

Using a power supply and a fixed resistor to set the current is non ideal as slight variations in output voltage will result in changes to the current, as well as during initial turn on (PSU may overshoot). Differences in forward voltage drops across the LEDs themselves will change the operating current, calculations will get you into the ballpark (which is good enough for stuff running at say 20mA for indication purposes) , but not really ideal when you're running high power (overdriving them above design limits will cost you LED life, and $$$), best if you go this method is to verify you're running at a safe current with a multimeter after you've put everything together, the forward drop will actually vary with life and current (check the datasheet for nominal values).

Controlling LED junction temps are important as well, the temperature will affect colour, as well as overall lifetime. Best to run them at a nominal current to get more life and use a few more LEDs for the required brightness.