This is relevant to your interests.
- A shadow is an interruption of light. Basically, if there is an object that could cast a shadow large enough for your PC to use (half their size) then you can use it. For HiPS, this is super easy because you just have to be within 10 feet of such a shadow. For SJ, it's effectively "object to object" since there's no real way to legitimately determine shadow length with time of day or whatever. So just try to get near and object that could conceivably cast a big enough shadow, for day time, and go hog wild at night time or in dark indoor areas - anything that isn't bright or well-lit, basically.
For lights, it's really simple. Don't HiPS or SJ directly beneath light sources. Most torches have a range of like 5 or 10 feet bright light, then it gets dimmer and is shadow for SJ purposes. When you're walking around with your PC, you can even see this difference - if you are in one of the dark tunnels that has a torch, enter into the range of the torch and you'll notice it gets bright immediately close to you, but everywhere else appears darker by contrast. Once you move away from the torch, everything becomes closer to the same level of contrast. So within the high contrast area - no SJ. Outside of it, go for it. Dark caves all the way.
Light effects, whether the spell or your gear, radiate from your PC and everything they are wearing while they are wearing or wielding it. As mentioned above, all gear carried/worn by the PC is considered a part of them for this. If they take off their gear and discard it on the ground, it stops glowing (unless the spell was cast directly on that object, or it is enchanted with Light, itself). Light cast on a PC is cast on the person itself unless otherwise specified for some reason.