Can you provide more detail? Did you study this or watch an episode of Bill Nye. I'm honestly curious to know more about IR light.
No, it was my hobby to build and construct lasers and similar so i did quite some learnings.
The IR that is being thrown into your face is like a led light. It cannot be more powerful then the back led, because the heatsink is too small and simply cant be much more brighter then the back LED. Because the light being scattered over your face like a flashlight, there is no damage done. (just like you can easily watch the back led of the device, even though its not comfortable)
Furthermore, the dot projector is even more weaker. Here is a image of a kaleidoscope of a laser:
https://www.lucklaser.com/images/50mw-Green-Laser-Pointer-Kaleidoscope (2).jpg
These laser pens (wich already have a WAY bigger heatsink then in the iphone x) have maximum 200mW of power(rare though) wich is definatly harmful to the eyes, but thats ONLY if the single dot, all power combined would hit your eyes. Looking at how many dots it projects, how much power is lost by the glass in the kaleidoscope, i'd estimate every dot that hits your eyes is maximum around 0,5mW. Thats perfectly save, and thats for one of those pens. (5mW is considered save for selling at stores, >5mw is forbidden to sell in most of the world)
Because the tiny size of the iphone and the heatsink, the iphone x simply cannot be powerful enough to be 200mW. Maybe, because it runs for a smaller period of time, it can achieve ~20mW maximum, i'd say. It will then run alot of dots over your screen to measure you, just like the kaleidoscope does. So the total power that can hit your eyes because those dots and cause damage is nihil. Zero. More arguments can be made that this unlock method doesnt affect battery life much, wich makes me believe the total power of the front IR lights are even less then that 20mw.
Apple doesn't have to come up with technical details about what they use because it's not remotely possible to damage your eyes with the power used in the iPhone X leds/laser.
Tldr:
It's simply not possible with the size of the module to do any damage to your eyes. Not remotely.