Translation:You find lamps and telephones inside.
Another correct solution includes use of the word 'can', which was not allowed earlier on in the course and it kept catching me out, and I presumed it was because there was no 'tud' or 'hat/het' in those sentences and it was important to for the course to differentiate this to the learner. Is it technically correct in this particular translation to use 'can'? Or is it an unintended inconsistency?
In Hungarian, "találsz" is the correct verb form to use if the lamps and telephones are certainly there. In English, you would start your sentence with "You can find" to express this.
In Hungarian, "találhatsz" would be used to express that one may find lamps and telephones inside, but the speaker isn't sure about their presence or the listener's ability to locate those objects.
Anyone know what's wrong with "You find the lamps and telephones inside"? Does "találsz" always include the idea of "can", or is there something special about this case?
"Találsz" in most of the cases is used as iRBiS' comment explains. But I think your sentence was incorrect because of the definite article, which is not present, nor implied in the Hungarian sentence.
Why is "You will find lamps and telephones inside" incorrect when it said találsz?
"you will find" is considered future tense in English; maybe that is why it didn't accept it as the Hungarian does not specify future.
On the other hand, I believe Hungarian does not use the future as much as English? So that may be a reasonable translation as well.
In which case, it would be merely one of many missing correct alternative translations; in that case, report the missing alternative.
However both can be right, it's more common to use a time word and the present tense to express future intent. If you say an exact date and/or time or even just imply that something will happen in the future, the verb can be in present tense. "I'll tell you later" can be translated as "Később elmondom" (the verb is in present tense, but you already know it will happen in the future (később=later)) as well as "Később el fogom mondani" (which is the clear future tense). Usually we use the latter the emphasise that the speaker has the intention to perform such an action.