In practical terms how are IR lights rated? Since IR light is not visable it can’t be tested using a Lux meter. All of the IR light ratings I have found are shown in MW. Are IR lights rated in MW using a standard electrical equation? Power supply would be a known voltage 3v or 6v. And the resistance of the LED should be a measurable value. Does that give you the MW rating?

if you are looking for application use, the ir output of an led is measured in radient intensity of mW/sr.

practically, you see no one use that, and you see a mW or W output derived from the forward voltage x current.

this doesn't mean much anymore, as newer ir led's have better efficiency and higher output, but gives people an idea of what kind of quantitative output to expect

IR LEDs are measured in radiant intensity (example, 1000mW of radiant intensity). You would need a good Light Intensity Meter that can measure radiant  intensity from the source. The amount of energy  going to the IR source isn’t going to help you much because most diodes and LEDs will require different amounts of current to produce the same amount of energy.

Edit,
cm beat me to it.

Thank you for the explanation. I was trying to figure how the advertised ratings were calculated. And trying to figure out why the cheap IR lights don’t advertise any ratings. I assume they don’t want to invest in the equipment to test thier products. Or the test would prove to be poor output ratings compared to other options.

This is very true.

LEDs don't have a static resistance to a voltage, or rather, their resistance changes quite a bit and isn't that predictable, so they recommend using a constant current driver in these applications.

Some power is dissipated as heat, and some as light. Negligible amounts would be dissipated as magnetic field.

Power is measured in mW/Sr - A Steradian (SR) is a conical surface taken on the inside of a hollow sphere - It's a "two dimensional" angle.
https://en.wikipedia.org/wiki/Steradian

However light intensity can vary quite a bit, and the reflector and other aspects such as the lens are critical to a good design if your objective is to illuminate things at a distance. Other objectives might be to eliminate or minimize side lobes - that is, the area around the main beam where the light source is very visible, but the light that arrives on-target isn't bright.

You can use a normal lux meter to measure IR light, if you know the sensitivity distribution of the sensor. My laser meter has a mW scale output, but there's a graph to provide a typical co-efficient that it should be multiplied by in case the light isn't at an optimal wavelength, and this is used to provide an estimate of an IR laser's power.

A single measurement in mW doesn't measure the beam width so won't provide a lot of information about how much light arrives on the objective.

If you don't have a scale, then assuming you can calibrate one, you can use a normal lux meter in many cases.

David