I have no experience with LiFi, or any visible-light data transfer. I do have experience with infrared ALS. It works really well if:
- you have a herkin' emitter
- that you're facing
- in a room without sunlight
this thing is about 200 high-output infrared LEDs blasting their hearts out. You can't really use them in single-channel mode because you want redundancy so you either have two or you run it in dual-channel mode. It's good for about 4-5000 square feet (contrary to their assurances of more) which means it'll hit one medium-sized lecture hall. And it will work only if the receiver is literally under your chin, where it's basking in the light of this thing.
Wanna transmit data for tablets or laptops? Well, now we have to move it overhead. Which means we need a lot more of them. basically they'll be in the same place as light fixtures. And they're going to have to be on a network... the same as light fixtures. And they'll be pumping out more energy than your light fixtures because your light fixtures are also putting out a crapton of noise in that wavelength unless you filter it off, which gets really inefficient for infrared and completely implausible for red. So in the end, you have two sets of light fixtures, one for you and one for your computer, and the one for your computer uses more energy and costs more.
That's why nobody's really fucked around with it much until it becomes part of the light fixtures, I reckon. PWM the shit out of the lights and you won't even notice the flicker and if you have the bandwidth, you can even put multiple channels on the same carrier. Just in my perusal of "white LED switching speed" it seems like 100MHz is a good number... which is not fast. Lasers? Terahertz.