Ya büyüteci ya da morötesi ışığı kullanacağız.

It means either ... or ....

So:

• ya büyüteci ya da morötesi ışığı = either the magnifying glass or the ultraviolet light

A very common pattern in Turkish is:

• ya X ya da Y = either X or Y

You may also see:

• ya X ya Y
• X ya da Y

But ya X ya da Y is a very standard, clear form.

You do not always need the full pair, but this full pattern is very common.

Possible variants include:

• Ya büyüteci ya da morötesi ışığı kullanacağız.
• Ya büyüteci ya morötesi ışığı kullanacağız.
• Büyüteci ya da morötesi ışığı kullanacağız.

The full version with ya ... ya da ... sounds especially clear and natural when you want to emphasize a choice between two options.

Because büyüteç is receiving the accusative ending.

Base noun:

• büyüteç = magnifying glass

With the accusative:

• büyüteci

This happens because of a sound change. When some Turkish nouns ending in ç, k, p, t take a vowel-initial ending, the final consonant often softens:

• ç → c
• k → ğ / g
• p → b
• t → d

So:

• büyüteç + -(y)i → büyüteci

The final ç changes to c before the vowel of the ending.

This is another common consonant softening pattern.

Base noun:

• ışık = light

With the accusative ending:

• ışığı

What happens:

• ışık + -(y)ı
• final k softens to ğ
• result: ışığı

So this is similar to:

• renk → rengi
• çocuk → çocuğu
• kitap → kitabı

This kind of change is extremely common in Turkish.

Because they are direct objects, and in this sentence they are treated as specific/definite options.

The verb kullanmak means to use, and it takes a direct object. In Turkish, a specific direct object often gets the accusative ending.

Here, the speaker is talking about specific things:

• the magnifying glass
• the ultraviolet light

So Turkish marks them as specific objects:

• büyüteci
• morötesi ışığı

Compare:

• Bir büyüteç kullanacağız. = We will use a magnifying glass.
  (non-specific, usually no accusative)
• Büyüteci kullanacağız. = We will use the / that magnifying glass.
  (specific, accusative)

In your sentence, both alternatives are specific, so both appear in the accusative.

Kullanacağız comes from the verb kullanmak = to use.

It breaks down like this:

• kullan- = verb stem, use
• -acak / -ecek = future tense marker
• -ız / -iz / -uz / -üz = we

So:

• kullanacağız = we will use

The exact form changes because of vowel harmony and sound changes, which is why you get -acağız here rather than a simpler-looking form.

Because Turkish normally puts the main verb at the end.

A very typical Turkish sentence pattern is:

• Subject + object + verb

So this sentence follows a normal Turkish order:

• Ya büyüteci ya da morötesi ışığı kullanacağız.

Literally, the structure is more like:

• Either the magnifying glass or the ultraviolet light we-will-use.

This verb-final order is one of the biggest differences from English.

Yes, Turkish word order is flexible, but not all changes sound equally natural in every context.

For example, you could also say:

• Ya morötesi ışığı ya da büyüteci kullanacağız.

This simply switches the order of the two choices.

You can also move elements around for emphasis, but the most neutral version usually keeps the verb at the end and keeps the ya ... ya da ... pair together.

So for learners, the safest pattern is:

• Ya X ya da Y kullanacağız.

Often, yes.

Both can mean or.

For example:

• büyüteci ya da morötesi ışığı
• büyüteci veya morötesi ışığı

Both are possible.

However:

• ya da is very common in everyday speech
• veya can sound a bit more formal or written, depending on context

Also, in the pattern either ... or ..., Turkish very often uses ya ... ya da ..., not veya in exactly the same way.

So in this sentence, ya ... ya da ... is the most natural choice.

Morötesi means ultraviolet.

It is built from:

• mor = purple / violet
• ötesi = beyond, the beyond of

So literally it is something like:

• beyond violet

That matches the idea of ultraviolet in English.

In morötesi ışığı, the word morötesi describes ışık:

• morötesi ışık = ultraviolet light
• morötesi ışığı = the ultraviolet light / ultraviolet light as a specific object

This word can be tricky for English speakers.

A few points:

• ı is not the English i
  • it is a back, unrounded vowel
  • roughly like a dull uh sound, but shorter and tighter
• ş = sh
• ğ usually is not pronounced as a strong consonant in modern Turkish
  • it often lengthens or smooths the vowel before it

So ışığı is approximately:

• uh-shuh-uh
• with the middle and final vowels flowing together smoothly

It is better not to pronounce ğ like a hard g. In most standard Turkish pronunciation, that would sound wrong.

Yes. Turkish often leaves out subject pronouns when the verb already shows the person.

The ending in kullanacağız already tells you the subject is we.

So Turkish does not need to say:

• Biz ya büyüteci ya da morötesi ışığı kullanacağız.

It can say simply:

• Ya büyüteci ya da morötesi ışığı kullanacağız.

The we is built into the verb.

It strongly suggests only one of the two.

That is the point of ya ... ya da ...:

• either X or Y

So the meaning is that the speaker is choosing between two alternatives, not planning to use both.

If Turkish wanted to say both, it would use a different structure, such as:

• Hem büyüteci hem de morötesi ışığı kullanacağız.
  = We will use both the magnifying glass and the ultraviolet light.