How to control the temperature of the LED lamp below 40 degrees?

When the area of the cooling aluminum shell is large enough, how to control the temperature of the 15W LED lantern within 40 degrees?
There are three points to this question that need to be clarified first:

1, what is the temperature difference with your environment, that is, the temperature rise.

If the ambient temperature is 40 degrees, it is impossible for you to reduce this temperature to within 40 degrees, and it is impossible for the heat dissipation of an infinite area to reduce the temperature of a heating body to lower than the ambient temperature.

The general calculation formula is 75 square meters of surface area 1W heat (is heat, not LED power), which can ensure that the majority of the heat emitted by the LED is dissipated. The choice of radiator depends on the positive resistance of the LED you are using, the voltage drop, and the current you are adding to the LED (if more than 350mA, the percentage of the increased heat generated as a percentage of the increased total power increases).

2, whether the power supply is built-in or external, whether the heat of the power supply should be calculated;

3, when the LED heat isolated in the lamp can also achieve a very low external temperature, such as the current domestic LED lamps, the use of the so-called ceramic radiator, so when testing the temperature rise of the lamp, not only to test the temperature rise of the lamp outside, more reference is the LED junction temperature