just warm enough, still warmer than chinese black box led units. so again why should anyone want to pay a high price for something which is 99% asian manufactured ( capacitors, resistors, leds, etc). other than to have bragging rights. i will tell you, people want the bragging rights of having a name on the product it is really that simple. aquarium products are not the only place you will see this behavior, you will also see it in guitar amplifiers, effect pedals, keyboards, home stereos, televisions, and everything else. personally i have had better luck with the no name chinese stuff, people tout warranty of companies but here is the thing if you never need the warranty or the product fails after warranty expires anyway what good is paying a lot of money on brand x with wqarranty vs brand y without? i have had several danner mag drive pumps fail in under 6 months but i had an old jebao that is now on its 4th owner and still working as good as the day it was new.
anyway, back on subject. if the light or PSU is getting warm to the point of being hot there is a problem with it, an led fixture power supply should get no warmer than a laptop power supply or wall charge plug, if it does there is something wrong and electrical componants are getting warmer than they should be, i have cheap wall power supplies from like 2000 that have been plugged in 24/7 since the day they were bought and they feel cold to the touch and that is when they are actually in use. another point i would like to make on the subject is this, i have a 1600 watt PSU in my PC that is running high end parts ( threadripper, rtx 2080, and enough rgb to enduce seizures LOL) and this monster is cool to touch ( and yes it runs 24/7) and i run a system stress test every few days especially in the summer and it still runs cool to the touch. so again if the psu is running warm there is a problem with the circuit design or componants. i mean i cant actually compare the led unit you guys have to anythign as i do not have your lights and i personally dont own a kessil ( nor do i want one).
i have read things from other kessil owners claiming their lights "warm" was similar to that of a T5HO and in some cases a low wattage metal halide and that should NEVER happen from an led.