Welcome to the insanely complicated world of After Effects!
I'll try to answer your question simply, but as always, the answer is "it depends."
To get straight to the point, you often want to apply your desired effect to the layer you want to effect. Lightning is just a little different, in that if you don't see what you're looking for you just need to check the box that says "Composite on Original."
Perhaps you don't want to apply lightning to your footage because you want it to cover multiple items, so you would use a solid layer, in which case you already saw that no extra work is necessary to see the effect.
Adjustment layers are for affecting everything below them. A good example would be if you had a vignette or a general color correction you wanted to apply to multiple layers. Rather than being inefficient and applying the exact same effect to multiple layers, you apply it once to an adjustment layer and you're done. This also makes tweaking very easy. Imagine changing your mind about the feathering on your vignette and having to go through multiple photos or video clips to change a single parameter. Be careful with adjustment layers because you can't exclude layers from their effects—meaning, anything below the adjustment layer will take on the properties.
Shape layers are amazing, and not something I could do justice to by explaining in a sentence or two. To summarize, you can have shapes or paths and do amazing things with them. If you work with Illustrator artwork you can convert that art into editable shape layers in Ae, as well. This isn't a type of layer you want to add the lightning effect to in this case; you're much better suited with an a solid, adjustment layer, or the footage itself.
One more tip about adjustment layers: any layer can become an adjustment layer, so really they're just solids with the Adjustment switch selected. Check out the screenshot to see what I mean.
My question is, how do I know which kind of layer (and I note some effects work directly on a video layer directly) to use for each effect?
There is no distinction here. You are simply applying a wrong workflow and mixing up things. You are applying an animation preset, not an effect. A preset stores the state of effects and settings, not the effect itself. In turn, any effects used in the preset still have all their options intact and in case of the lightning effects this simply means you need to enable the "Render on Original" option. Other effects have similar settings. Any discussion beyond that is not necessary. You just need to learn and understand AE's rendering pipeline and how each effect works.
In general terms you want to use a new layer for each effect. Lightning does have the option to composite on original which would allow you to add lightening directly to a video layer. In the real world a lightning strike would also illuminate other things in the shot. Let's break down a frame from some video of a real lightning strike and see how many layers you would need to create the same shot in a video. I found this on YouTube.
Let's start by analyzing what we see. This is a scene with a tree in the foreground, some structures in the middle ground and in the background, the lightning bolt, the light from the bolt backlights the mushroom shaped structure in the left center of the frame, causes a lens flair in the center of the frame, side lights a bunch of other elements in the frame, causes the sky to glow, and puts highlights on some of the leaves. Fortunately lightning strikes happen very quickly so we don't have a lot of frames to worry about but we will need a lot of layers. Here's one approach Starting from the bottom:
- A couple of shape layers to act as reflections on the trees that are slightly blurred and applied using the ADD blend mode
- A copy of the original footage with the foreground tree rotoscoped to put above the glow created by the lightning flash
- A gradient layer masked to the counter of the ground to create the glow in the sky with a soft edge mask and applied using the Screen blend mode
- A hole out mask for the mid ground elements - everything but the tree that is between the camera and the lightning strike
- Semi transparent "glow" layer or layers to add lighting to the building and the other elements in the scene using blend modes and opacity
- A Central core for the lightning strike that can be created using a copy of the lightning strike that is blurred to be composited on top of the strike using the Add blend mode. To get this to work properly you may have to pre-compose several copies of the strike, set the blend mode of each copy to Add and increase the blur on each layer
- An animated ball of light where the strike actually hits the ground created with a blurred shape layer using the ADD blend mode
- An additional layer to simulate the light spreading on the ground using blurs and blend modes
- The actual lightning effect applied to a separate layer and composited using the ADD or screen blend mode
- The original footage
I have done thousands of visual effects shots in my life that simulate everything from lightning strikes and explosions to fires and car crashes, to gunshots and knife wounds. Many of them could have been done with one or two layers and a bunch of stacked effects, but most of the time it's faster and more efficient to just add a layer for each element you want to add to the scene and use masking, roto, and blend modes to make them work. Some of my composites have had a hundred or more layers.
I hope this helps. I would highly recommend spending some time over at Total Training or Lynda.com to get some training in compositing. I would also recommend anything written by my friends Chris and Trish Meyer. You'll also want to check out Pro Video Coalition and Video Copilot.
The biggest mistake a new user of After Effects can make is to jump right in and try and figure out how to do visual effects without spending some serious time studying and experimenting. I've been doing visual effects since we had to paint masks on glass plates we put in front of the camera and double expose film. This is an old science that is really not more than cutting out paper dolls and pasting them on a background.
Rick Gerard wrote:
Lightning does have the option to composite on original which would allow you to add lightening directly to a video layer.
Great write-up, Rick!
To your point, you're right, I should have specified. Lightning is an obsolete effect, and is categorized as such. Advanced Lightning has the Composite on Original option.
Many thanks for your input on this. I realise I have to acquire a significant amount of knowledge and skills to understand and make use of AE.
For some context, I’ve only ever used AE for extremely lightweight tasks, but I’m now investing the time to learn and use it properly. So I am learning from square one, but curiosity about functions AE is capable of (and the need to have a little playtime after serious studying) did make me dabble and experiment on the “what if I try this or that” route, hence the query regarding effects on layers.
Rick, your reply to my original question is inspiring. I doubt I have enough years left on this planet to come anywhere close to your level expertise, but I enjoy learning so will do my best. I have a subscription to Lynda.com which is useful, but I prefer good old fashioned books where possible.
Many thanks once again to you all for your contributions on this thread.