Affected/Effected

"Affect", in the example you've given, means to influence or produce an effect on something. In normal usage it is always a verb; it has a noun meaning only as a term used in psychology.

In contrast, "effect" is most often used as a noun. It means the result of an action.

It is easy to see why confusion can arise: when an action affects something, it produces an effect. When wondering which to use, remember that "affect", in normal usage, is always a verb. "Effect" can be a noun or a verb but is usually a noun. As a verb, it means to bring about or accomplish something, as in:

We've effected the design changes as requested. (we've made the changes)
In recent years, the government has effected major improvements to the health care system. (the improvements were successfully implemented)

It is "effect" -- not "affect" -- that frequently appears in compound nouns, prepositional phrases, and phrasal verbs. Examples:

personal effects
special effects
Doppler effect
greenhouse effect
come into effect
bring into effect
for effect
give effect to
in effect
take effect
to the effect that
to that effect

What about:

Epilepsy may be affected/effected by strobe lighting

By selecting the general term epilepsy to stand for two more specific ideas, you seem to be trying to make it appear that affect and effect somehow mean the same thing.  But the mere fact that two different words can be placed in the same position in a sentence proves nothing about synonymy, witness:  What a beautiful cat/dog you have!  or I would like to write/read a book.

Disambiguating the two uses conflated in your one sentence shows more clearly what the difference is between the two verbs affect and effect.

A person with epilepsy may be affected (influenced) (to have a seizure) by strobe lighting.

An episode of epilepsy (a seizure) may be effected (caused to come about) by strobe lighting.

CJ

concerning: "What he thought would be [affected/effected] looks like what will be [affected/effected]."

Just to clarify, the reason both sentences can mean the same thing is that the subject is unspecified.

In one case the subject is what is being influenced, and in the other the subject is the influence itself.

When affected is used the literal meaning would be something like: "What [thing] he thought would be [influenced]..."

When effected is used the literal meaning would be something like "What [influence] he thought would be [brought about/accomplished/put into operation]..."


Looking strictly at the dictionary definitions from several dictionaries it seems the most memorable rules to use instead of the "accepted" rules would have to be something similar to the following:

1) Use affect[ed] when referencing a mental state (usually an emotion attachment).
2) Use effect[ed] when referencing a change or influence (including the change from non-existence to existence).

Under the old rules, affect[ed] has two meanings, one of which logically conflicts with the meaning of effect[ed], so these new rules essentially just remove the conflict, and leave both words with a single meaning.

I personally will no longer use the old rules, they seem very ridiculous to me.  After all, nothing is accomplished without influence, and there is no influence without accomplishment, If we really mean "influence" or "accomplish", or any other word representing a shade of the meaning of change, we can use those words instead.