There are two European standards for professional use: EN 471 class 2 and the more demanding EN 471 class 3. The less demanding EN 1150 standard is for non professional use only, such as in sports. There are also closely corresponding American ANSI and Canadian standards, but they are quite irrelevant in the European market (though most professional products meet both EN 471 and Ansi, since they are so similar). I have no idea what the French law viz bicycling presupposes, but I would guess EN 1150. However, most professional gear meets at least EN 471 class 2, and ussually even class 3 (apart from many gilets and t shirts that are simply not large enough to meet class 3 requirements, but make do with class 2).
Instead of worrrying about what you can get away with, I think the smart thing to do is to get the best there is: EN 471 class 3. It does not cost any more, and it is designed for the most demanding situations for road side workers - that is precisely the gear a cyclist wants, I think.
The practical problem is that there really is hardly any cycling specific gear that meets these standards. There is clothing with a hi viz yellow colour, but nothing that also has reflective striping of the kind required by any of the standards. All you can hope for is a bit of piping and small reflective details.
The question is what to do, other than wear an EN 471 vest at all time. I have chosen to buy some hi viz yellow Brooks Nightlife running shirts, socks, and a jacket. As sports clothing I have been very happy with the stuff, and as long as you are riding in day time or at dusk, the dayglow colour is magnificently visible. The problem comes at night. Then the fluo colour no longer works, and you really need the reflective striping. Since that is also the colder time of day, the absence of such striping on my thin shirts does not really bother me: I will be wearing some jacket in any case. I have stuck some reflective stripes on my Goretex and Windstopper cycling jackets, and that does a decent job, even if it does not meet any standards. To really meet those standards, I either need to wear a professional workwear vest, or buy an EN 471 Goretex workwear raincoat. The bad news is that the latter really are rather heavy.
So I make do, in the absense of serious cycling specific clothing that meets EN 471 standards, not even class 2. The fact that there is none (at least that I know of), really is a disgrace.
Willem