I see lots of vehicles that use the front turn signals as DRLs. Have these been designed any differently than their non DRL counterparts?
Turn signals originally intended for use as DRLs are designed to produce at least 500 candela axial intensity, which is the same minimum axial intensity as turn signals located within 4" of a low beam headlamp or a lamp providing the daytime running light function.
I can't seem to find any actual regulation on the use or design of DRLs.
US Federal Motor Vehicle Safety Standard 108 and Canadian Motor Vehicle Safety Standard 108 contain those requirements. Some provisions may be referenced to SAE J2087.
I know that turn signals have to meet certain photometric requirements, but do DRLs?
The design, construction, performance, durability, installation, and electrical hookup are specified in detail for most exterior light functions, even those that are not legally mandatory, such as DRLs in the USA.
I would like to make mine into DRLs if it is legal
Yes, it is generally legal to do so. There's a module available
here to add that function properly to a vehicle originally not equipped. It works well in most cases, but ask the vendor about your particular application; there are some vehicles with front turn signals that won't tolerate the extra heat of steady-lit operation. There are also some turn signals -- especially on very old cars -- that are too dim to provide much of an effective DRL function. Sometimes they can be improved by various techniques; other times it's best to consider an alternate way of adding a DRL function.
