Přímé sluneční světlo není rozptýlené světlo.

A word-by-word breakdown is:

• přímé = direct
• sluneční = solar, of the sun
• světlo = light
• není = is not
• rozptýlené = diffused, scattered, dispersed
• světlo = light

So the structure is basically:

• Přímé sluneční světlo = direct sunlight
• není = is not
• rozptýlené světlo = diffused light

Because both adjectives describe the noun světlo:

• přímé tells you what kind of light it is: direct
• sluneční tells you where it comes from / what it is related to: sunlight / of the sun

So přímé sluneční světlo means direct sunlight.

This is normal in Czech. Multiple adjectives can come before a noun just like in English.

Because Czech adjectives have different declension patterns.

• přímé and rozptýlené follow the common adjective pattern where the neuter singular nominative ending is -é
• sluneční belongs to a different adjective type, often called the soft pattern, where the nominative singular form is -í

All three adjectives still agree with světlo, which is:

• neuter
• singular
• nominative

So even though the endings look different, they are all grammatically matching světlo.

Both instances of světlo are in the nominative singular.

• Přímé sluneční světlo is the subject
• rozptýlené světlo is the predicate noun phrase after není

The adjectives match that same case, number, and gender.

So the whole sentence is built with nominative forms.

Yes. Není is the negative form of je:

• je = is
• není = is not

In Czech, this is not normally made by putting a separate word like not after the verb. Instead, the negation is built into the verb form itself.

So:

• To je světlo. = That is light.
• To není světlo. = That is not light.

Because Czech does not have articles.

So světlo can mean things like:

• light
• the light
• sometimes a light

The exact meaning depends on context.

In this sentence, the statement is general and classificatory, so English also naturally uses bare nouns: Direct sunlight is not diffused light.

Yes, you could say Přímé sluneční světlo není rozptýlené, and it would mean:

• Direct sunlight is not diffused

That is grammatical and natural.

But repeating světlo changes the focus slightly:

• není rozptýlené = says it is not diffused
• není rozptýlené světlo = says it is not diffused light

So the full version sounds a bit more like a definition or classification, not just a description of a property.

Because sluneční and slunný/slunné do not mean the same thing.

• sluneční = of the sun, solar
• slunný = sunny, sun-filled, having a lot of sun

So:

• sluneční světlo = sunlight
• slunný den = a sunny day
• slunný pokoj = a sunny room

Using slunné světlo would sound odd or would at least not be the normal way to say sunlight.

This is a good grammar question.

After být and nebýt, Czech can sometimes use either:

• nominative
• or instrumental

But in simple statements of identity, classification, or definition, the nominative is very common and natural.

So here:

• není rozptýlené světlo = a straightforward classification statement

The instrumental version není rozptýleným světlem is not impossible, but it sounds more marked and is not the most neutral choice here.

For a learner, the safest understanding is:

• this sentence uses the normal nominative predicate structure

Czech word order is flexible, but the given order is the most neutral here.

Přímé sluneční světlo není rozptýlené světlo presents:

• the topic first: direct sunlight
• the new information second: is not diffused light

You could reverse the two noun phrases:

• Rozptýlené světlo není přímé sluneční světlo

That would also be grammatical, but the emphasis changes. Now the sentence starts from diffused light instead.

So the original order is natural if the topic is direct sunlight.

Two tricky parts are:

• ř in přímé
• ě in světlo

Helpful approximations:

• přímé sounds roughly like pzhree-meh, but the ř is a special Czech sound that combines something like r and zh
• světlo is roughly svyet-lo

A few more pronunciation notes:

• Czech stress is normally on the first syllable of each word
• í is a long vowel, so pří- is longer than a short i
• ě often creates a ye / je-type effect after certain consonants, so světlo is not pronounced like plain svetlo

If you want a practical learner approximation, say:

• PŘÍ-mé SLU-neč-ní SVĚ-tlo NE-ní ROZ-pty-le-né SVĚ-tlo

That will get you fairly close.