XML Heat differences Neutral vs Cool White?

I have recently swapped my XML T6 Cool White on a aluminum 20mm star with a T5 Neutral White on a aluminum 20mm star and it seems to get noticeably hot faster. The voltage was kept constant(same battery) with the same current(tail cap measurement). I'm just wondering if it's normal for this? or is there something wrong with my T5? The pcb board seems to have the same thickness.

Unless both leds have the exact same forward voltage you can not compare them when run from a battery.
In general the neutral ones are less efficient and thus run hotter.
Are the stars the same?

They are not the same, I ordered the XML pre-soldered to the board. They're about same size and thickness, 20mm aluminum star board, but just ordered them from different places. The T6 is from DX and the T5 is from Ledgroupbuy, although my initial assumption is that aluminum used in the T5 is more pure therefore better thermal conductivity? but I'm just a bit curious since there's around a 30-40%(estimated from touch) increased in heat from about the same voltage and current (only swapped the star with everything else constant). I would assume that the Vf is the same if not very close since they are both XML's.

if one is better heatsinked than the other, it will feel hotter. What thermal paste did you use?

jorn said:

if one is better heatsinked than the other, it will feel hotter. What thermal paste did you use?

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That is my guess too. You did a better job with the heat sink when swapping the cool to the neutral.

Swapped led's on my stubby quark turbo (single rcr), and my Itp H01 headlamp today. Both now got a hi cri xp-g and they both feel hotter then they were. Used artic silver thermal addesive and a lot of pressure, so i expeted that.

I can't remember the type of Thermal Paste I used, since I don't have it here atm, but it was some generic brand and I did mod the first Cool White star too.

jorn said:

if one is better heatsinked than the other, it will feel hotter. What thermal paste did you use?

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Maybe I didn't put enough thermal paste with the Neutral? LOL. For the Cool White, I actually put a little too much on, since it was oozing out a little bit. But as far as contact I believe it should be around the same, since the base of the reflector actually presses fairly tight on to the board.

liteFOB said:

Maybe I didn't put enough thermal paste with the Neutral? LOL. . . . .

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If the LED is generating the same amount of heat and you increase the Thermal Resistance, then the body will be at the same temperature, but the LED chip will rise to a higher temperature. The ability of the torch to dissipate heat to the atmosphere depends ONLY on the torch body.

IF THIS IS DIRECT DRIVE ? and the LED chip operates at a higher temperature, the LED voltage will reduce, causing a significant increase in current, and therefore heat output.

tre said:

That is my guess too. You did a better job with the heat sink when swapping the cool to the neutral.

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This is my guess as well. I switched an emitter/star out on a light and was generous with the thermal paste, it seemed to get hotter then the stock version.

liteFOB said:

Maybe I didn't put enough thermal paste with the Neutral? LOL. For the Cool White, I actually put a little too much on, since it was oozing out a little bit. But as far as contact I believe it should be around the same, since the base of the reflector actually presses fairly tight on to the board.

Click to expand...

Maybe you used too much or too little on the cool white version, or it wasn't clamped as well. From my understanding too much paste can be bad as well as too little paste. If the body of the light is getting hotter that is a good thing, it means you are drawing more heat away from the LED. If the body of the light is cold then heat is not being drawn away from the LED and the LED will age prematurely if driven hard.