English always writes its acronyms in capitals. Sure, there is a sprinkling of exceptions where they’re pronounceable and have escaped into widespread use (such as laser, radar, snafu and scuba) but they’re few and far between. Even LED and VAT haven’t got that far yet, though they may before long.
So don’t lowercase them. Here are a few good sources to look out for, with examples:
- computers and technology: LAN, WAN, ICT, SMS, HTML
- file types as a descriptor retain their status as an acronym, but not when you’re quoting the actual text as typed. So:
- a .jpg file is in JPG format
- a PDF file has the extension .pdf
- this includes compound words: Dutch can write led-lampje or usb-stick, but English still keeps the capitals for the acronym part
- btw => VAT
- TV, DJ, OK, X-ray retain their capitalization
- Dutch uses a lot of initial-capital acronyms for its laws (e.g. Wft, Wbsn-z, Wmo, Wwft). Don’t take that habit across into your English.
There are occasional cases that have clearly been designed to be pronounceable and you do regularly see those with only an initial capital: Unesco, Stasi, Concacaf. This is generally accepted but some editors will regard it as not really correct. Company names: stick with their own preference.
Prevalence: moderate. Dutch authors do seem largely to be aware of the issue, probably because it can be contentious in Dutch as well at times.
Frequency: high. Particularly in financial, legal and ICT texts.
Native: rarely. Filetypes sometimes, and ones that are designed to be pronounceable.