Didier Fourcot Apr 18, 2016:

@Tony and asker The most prevalent reason to install "diffuseurs" in France on LED luminaires is the Inserm study: point LED sources are found dangerous for the eye:
http://www.quechoisir.org/equipement-de-la-maison/bricolage-...
http://www.consoglobe.com/ampoules-led-nocives-sante-4531-cg

Tony M Apr 18, 2016:

@ Asker #3 Note that all this is becoming more important because of the advent of LED light sources.
Normally, with traditional sources like fluoresecnt tubes, CFL lamps, etc. the source is already partly diffused by the technology itself; hence the aim is to use as little diffusion as possible, in order to let as much light through as possible and hence improve lumious efficiency.
However, LED light sources are relatively tiny pinpricks of light, and (except for deliberate special effects) are normally disagreeable to the eye and produce unwanted glare. Hence quite a large amount of diffusion is needed, in order to make the light source appear as large and diffuse and more-or-less even as possible. But the heavier the diffusion, the greater the light loss, and hence, the lower the overall efficiency — this is why currently lumnaires usually have 2 specifications for luminous efficiency: one, the actual efficiency of the actual light source, and the other, the efficiency of the luminaore a a whole.
Hence why manufacturers seek to find lexical ways to dsecribe the different degrees of diffusion, which are otherwise difficult to illustrate.

Tony M Apr 18, 2016:

@ Asker #2 Note too that SOME manufacturers make a specific distinction in EN between just 'opal' and 'opaline' — they all seek to explain the different degrees of diffusion, and many different terms are used. So there might be a fine distinction being made here between different grades of diffusion — with little if any reference to the kind of 'opalescent' effects traditionally associated with these terms.
However, once again, it may simply be inaccurate use of the term in your source text, in which case you would indeed need to consider it as being simply 'opal', as some answerers have already suggested.
So it would help to check the provenance of this "English" text, and also look at your wider context to see if these technical distinctions are being deliberately made or not (and I personally suspect NOT!)

Tony M Apr 18, 2016:

@ Asker I have quite some doubts about the authenticity of the EN in your source text; I fell pretty sure it is either already translated (from NL?) or was written by a non-native speaker of EN. the key clue to this is the incorrect use of 'actual', which in En does NOT have the meaning clearly intended here that would be 'actuel' in FR! In most contexts, 'actual' in En means 'réel' in FR, and the meaning they are looking for here is that of 'current' or 'present'.
This doubt about the provenance in turns casts a doubt upon the technical accuracy of the rest of your terms!
'optic' is not all that common in EN for luminaires (not least beacause it is found more commonly in EN in the plural, like so many other FR words in '-ique, cf. logistique > logistics) — and strictly speaking/u> ought only to be used when it has some specific effect directing the light, for example, lensed or prismatic; otherwise, it is simply a 'diffuser' ('diffuseur') — which seems the much more likely explanation here, since it is unusual for 'optics' to be diffusing, which tends to defeat the object!