lu vs lux, What's the Difference?

Which to use

“lu” and “lux” are a confusable English pair: similar on the page, but distinct in meaning, check the gloss before you choose.

#12,273
“lu” frequency rank: #18,878
“lux” frequency rank: 31151
confusion score

Side-by-Side Comparison

Feature	lu	lux
Definition	Archaic form of loo (“card game”).	In the International System of Units, the derived unit of illuminance or illumination; one lumen per square metre. Symbol: lx

Where the eye mixes lu and lux

Muted = shared; highlighted = the visual trap. They share 2 letters in sequence.

2 ch

3 ch

lux

Look-alike desk: lu vs lux

A purely visual mix-up. lu (/luː/) and lux (/lʌks/) are said differently, so reading them aloud is the quickest way to catch the wrong one. On the page they stay close: they differ by 1 extra letter(s) - “lu” sits inside “lux”. Our composite confusion score for this pair is 31151, derived from the frequency rank of both members and their visual similarity.

lu is recorded at frequency rank #12,273, classified as anoun, pronounced /luː/. lux is at rank #18,878, tagged as anoun, pronounced /lʌks/.

Glosses for this pair are partially populated in our dataset, but the full side-by-side definitions above should still guide you to the right choice.

With a confusion score of 31151, this pair ranks #348,578 of 530,003 scored English confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of lu vs lux

Shared letters: lu. Private to "lu": -. Private to "lux": x.

"lu" · 2 letters · shape CV · "lux" · 3 letters · shape CVC

Frequently Asked Questions

Is swapping "lu" for "lux" ever safe?

No. They are said differently (/luː/ versus /lʌks/) and carry different meanings; reading the sentence aloud is usually enough to catch the wrong one.

Frequency check: "lu" vs "lux" - which ranks higher?

"lu" is the more common of the two: it sits at frequency rank #12,273 in our English list, against #18,878 for "lux". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

After this comparison

Eye-level mix-up between "lu" and "lux" is sorted above. Next: full entries or other pairs that share a letter shape.

Full dictionary entry for "lu" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "lux" - compare definitions side by side with the headword page. Word entry
This pair ranks #348,578 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
"lu" and "lux" also get mixed up with nearby pairs, the highest-scored neighbour is "LSC vs lux". Nearby pair

Confusion rank #348,578 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.