The Infrared Light Sensor in Phasmophobia is triggered by a ghost's movement and will emit a light for a short time after being triggered. So far I've not found much use for this item. A few of them in a small room might provide some lighting, but that would depend on whether or not you're dealing with an active ghost. However, where a candle does provide light and protect sanity, it can be blow out where these sensors cannot.
I have experimented with these sensors a few times and I can say that I don't find them that useful. They are expensive and are another item that you can lose if something goes wrong. However, you should feel free to experiment with them as you wish. You never know, you may just find that for your play style they are quite useful.