Lidar vs. LiDAR vs. LIDAR vs. LADAR: Letter Case Matters

How Did We Get Here?

Radio Detection and Ranging = radar
Light/Laser Detection and Ranging = lidar (LiDAR? LIDAR? LADAR?)

How did the spelling of these acronyms evolve/devolve? Collectively, the world develops colloquial words and phrases in professional and everyday jargon. At what point did the phrase ‘Light/Laser Detection And Ranging’ gain four acceptable versions of spelling: LiDAR (mixed case), lidar (all lowercase), LIDAR (all caps), and LADAR (all caps)? Lidar’s cousin acronym, radar, sheds light on the origins but not the divergent paths the spelling incurred. Eighty years ago RADAR popularity rose quickly as an important technology through regular and routine use, therefore lowercase radar became a legitimate word in the commonplace, much like SCUBA or LASER have today. Even military CARE packages have acronym origins. Common origins should lead to common spelling—but not here.

The n-gram model is a computational linguistics and probability model which attempts to predict the next item in a sequence, such as a word, syllable, or phrase in a sentence. Google’s Ngram Viewer charts, year by year, the twists and turns of cultural and professional trending vernacular within published literature utilizing this model. The Ngram Viewer can be an interesting tool to see how events affect trends. The Watergate scandal of 1972 shows an abrupt Ngram increase in 1972 as we would expect. The database records only go to 2008 because Google is busy scanning in our most recent literature, therefore events of 2009 to 2014 are nonexistent or just on the horizon, such as the iPad (which has no Ngrams). With ‘the vs. thee‘ argument we can see usage of ‘thee‘ has faded over time whereas ‘the‘ remained relatively steady in comparison. We can use the Ngram Viewer to search for various spellings for the same word too, such as lidar or LiDAR and U.S.A. or USA. The Google database is massive, having scanned millions of printed lit. The inclusion of text books and fiction alike, along with digital publications, allows insight into culture but also technologies. Please enjoy analyzing trends with the Google Ngram Viewer and see for yourself how common vernacular is evolving/devolving.

Figure 1 RADAR vs. RaDAR vs. radar (1930-2008, English) [i]figure1radar


The lowercase spelling for ‘RAdio Detection and Ranging’ was coined in 1939 by the U.S. military and the industry began using it as a standard immediately. We can see the spike in use around 1939 in Figure 1 above. Interesting to note the similar mixed case acronym for radar has never appeared in written text; “Ngrams not found: RaDAR.” This means no published literature in Google’s databases uses the mixed case spelled ‘RaDAR’ and only a small percentage have the all capitals versus the lowercase version.

Figure 2 lidar vs. LiDAR vs. LIDAR vs. LADAR (1950-2008, English)[ii]figure2lidar 


LIght Detection And Ranging’ (also with LAser for LADAR) had similar beginnings as RADAR, though the industry standard has taken on a variety of spellings in the last twenty years. As you can see in Figure 2 the mixed case use is gaining popularity whereas the lowercase version is diminishing. What purpose did the collective see by hyperbolizing a 50 year standard to a new one? Does ‘LiDAR’ look stronger, smarter, new-age, superior to its lowercase cousin? Is lidar and LIDAR the past, yet LiDAR the future?  The use of this technology (by any name) is becoming more prevalent, cheaper, and ultimately more important, therefore a standard should be solidified.
To add fuel to the fire and confusion to the community, LADAR is used primarily in Europe as a fourth possibility. LADAR is never found in all lowercase or mixed form, only all capital letters. LADAR changes the entire root origins because it is claimed the first letter stands for laser. Therefore, LAser replaces LIght. As to which is correct, laser or light? Written English leans toward light because laser includes the word light (laser: light amplification by stimulated emission of radiation) so an acronym would be ill-suited to include an acronym. The community seems to  be slowly fading LADAR usage out and never fading in a third acronym abbreviation, known as “Laser Infrared Detection and Ranging” (with only one all caps version).

What’s the Word?

With any written form, lidar, LiDAR, or all caps LIDAR, the versions are pronounced the same way. The pronunciation[iii] fits the same model radar gave us.

lī ‘– där =  “lī” as in lie  +  “där” as in dark
rā – där = “rā” as in ray + “där” as in dark

One word with multiple accepted spellings? That’s similar to a geographer allowing ‘GEOgraphy’ as an acceptable spelling. Google defines the origin of radar as an acronym, whereas the origin of lidar is a combination of “light+radar”. As that could be true, in reality the word ‘lidar’ is an acronym and should be treated in the same manner radar was/is/will be. As a collective group, the lidar community is steering the jargon to the newest of versions as a new standard however grammatically incorrect. It’s ultimately up to the user/writer to determine which spelling is best for the purpose of the document.

The DEM User’s Manual, 2nd edition[iv] remarks, “like radar and sonar, lidar is now commonly written in lower case” then proceeds to use lowercase lidar through the book. The manual is intended as an informative textbook relaying the physics, concepts, and history of elevation data collection and processing. To regard the word as a lowercase acronym shows awareness of the history and origins of lidar technology. The mixed case version shows up intermittently between 1979 and 1990 but gets a sudden bump in use around 1999. A widespread interest in lidar technology in the 21st century has led to a jumbling of uses, from the original acronym to the subsequent newest version, Figure 2 above. Interesting to note the large number of lidar references with a subsequent drop in lowercase references, which is unequal to the increase in references with different spellings, meaning the total references of all versions have dropped a bit (but only up to 2008, newer data may show a different inclination). Akin to radar, all capped LIDAR versions are an acceptable spelling, though unlike LiDAR, the mixed case RaDAR does not show up in literature. Both radar and lidar have all capped versions but have only appeared intermittently throughout the 20th century, with even less use in the 21st century. The two all capped versions of the acronym have been around just as long as the lowercase versions.

Final Thoughts

Figure 2 shows that lowercase lidar is not old news just yet and LADAR is the most obscure of all versions. Increases in popularity of the all capped and the mixed case versions (LIDAR and LiDAR) are beginning to battle for superiority in the 21st century as usage have only increases. The scientific community cannot decide on the correct way to phrase or spell this technology. Between the mixed case spellings of radar and lidar, even the origins of lidar are uncertain, whether ‘and’ should be capitalized, Figure 3. In reality, since each abbreviated word is an acronym, the common use should be all capital letters, akin to NASA or NATO. The ultimate answer to which is correct will be decided by the lidar community. The version that is used the most will inevitably become the victor.

Figure 3 LiDAR broken down into different versions (1960-2008) –  Light Detection and Ranging vs.  Light Detection And Ranging vs. Laser Detection and Ranging vs.  Laser Detection And Ranging (no Ngrams) [v]figure3and



  1. Thanks for your article. An interesting insight into how language happens.

    It just feels “to soon” in the life of the tech to go the same route as scuba, sonar and radar. And while my personal preference would be to use LiDAR (it just sounds “21st Century” to me), I think I’ll be going with Lidar, since that is the way our customer (Dept. of Energy) seems to spell it most often.


  2. Great to clear things up, thanks for the article! I am of the opposide opinion of Frank here, I think LiDAR (mixed case) is the worst of the alternatives, closely followed by LADAR and LIDAR. Currently writing an academic text and having “LIDAR” with all caps in every third sentence on every page really burns the eyes to look at. Will use the reasoning “like radar and sonar, lidar is now commonly written in lower case” and continiously use this in our article.


  3. The word lidar appears in the Oxford English dictionary as a portmanteau of light+radar. That effectively settles the question: that lidar is a distinct word, not an acronym. If you use an acronym in a publication it is because you are creating or selecting an acronym for the exact topic you are discussing. At that point, you can just make up your own acronym such as LMoT for laser mapping of terrain or LII for laser interferometry imaging. Why not? No need to juggle others’ acronyms. Or simply use the English word lidar rather than an acronym, and everybody knows what you mean.


  4. On the issue of what the truest and oldest origin is, the citation to Ring, James (1963). “The Laser in Astronomy” is often used to claim that the portmanteau-origin is the oldest. A few days ago I stumbled upon this site ( where they cite the use of LIDAR with the origin as an acronym: Middleton & Spilhaus, E.K. & A.F. (1953). Meteorological Instruments. University of Toronto Press. I have failed so far to find the full text to this citation, so I have not checked myself how Middleton & Spilhaus define their LIDAR notation.

    Anyway, in conclusion the acronym appears to predate the portmanteu by a whole decade! This is a setback for me, who supports the portmanteu-origin and lower-case school 😉


    • I completely agree that we should use the lower-case version and it’s interesting that there seems to be potential uncertainty about the origins. Instead of worrying about the exact origins, I prefer to take the view that it is similar to radar, which originated as an acronym and is now used as a word. I believe lidar is also sufficiently common that we should treat it the same way. Just my personal view though.


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