Learn French: Les colons ont moins de radiations dans la serre. - The colonists have less radiation in the greenhouse.

In French, expressions of quantity like moins (less/fewer), plus (more), and beaucoup (a lot) are followed by the preposition de without a definite article. Even though radiations is plural, the rule applies, so it must be moins de radiations.

Why is radiations plural in the French sentence but singular in the English translation?

In English, the word radiation is usually an uncountable noun, meaning it does not take a plural form. In French, however, it is perfectly normal to use the plural les radiations to refer to actual physical emissions or rays, especially in medical, scientific, or sci-fi contexts.

If I wanted to say 'The colonists have less radiation there' instead of 'in the greenhouse', which pronoun would I use?

You would use the pronoun y. Because dans la serre indicates a location introduced by a preposition other than de, y is the correct choice to replace it. The sentence would become Les colons y ont moins de radiations.