efficiency of dichroic reflectors

[Pawel Paron]

Does anybody know the numbers how much visible light is being wasted through
the rear of those cheap and popular dichroic MR16/MR11 bulbs? I'm using such
bulbs for my DIY high power bicycle lights, and I wonder if it's worth to
look for completely reflective, opaque reflectors (hard to find anything
usable for >20W bulbs, anything small and cheap is usually plastic, so those
MR16/11 fixtures are very attractive, but I doubt that they are most
efficient solution).

Regards
Pawel

 

[Steve Eckhardt]

Does anybody know the numbers how much visible light is being wasted through
the rear of those cheap and popular dichroic MR16/MR11 bulbs? I'm using such
bulbs for my DIY high power bicycle lights, and I wonder if it's worth to
look for completely reflective, opaque reflectors (hard to find anything
usable for >20W bulbs, anything small and cheap is usually plastic, so those
MR16/11 fixtures are very attractive, but I doubt that they are most
efficient solution).

Regards
Pawel

A reasonable "cold mirror" coating that reflects visible light and transmits
IR reflects an average of about 95% in the visible. Enhanced aluminum
coatings reflect about 94%, so you wouldn't be gaining much.

 

[Pawel Paron]

A reasonable "cold mirror" coating that reflects visible light and transmits
IR reflects an average of about 95% in the visible. Enhanced aluminum
coatings reflect about 94%, so you wouldn't be gaining much.

OK, thanks. So I'll stay with these MR bulbs, since they are most common and
cheap.

Regards
Pawel

 

[Mark Jongewaard]

OK, thanks. So I'll stay with these MR bulbs, since they are most common and
cheap.

Regards
Pawel

I worked on some MR-16 reflector designs for one of the main companies who
applies the thin film coatings to the glass reflectors. During the course
of that work we attempted to quantify the visible reflectance of the
coatings. There were difficulties with this but the net result was we
determined that the reflectance was in the mid to upper 80's. The process
of uniformly applying the thin film coatings into the particular reflector
geometries is difficult and as a result they aren't able to achieve what is
likely possible in more ideal geometric conditions using flat or at least
large and more open glass samples. This isn't such a problem for applying a
coating of just aluminum to make an opaque reflector, but it is for the
dichroic coatings in the MR-16's where they require many layers of specific
thicknesses. The bottom line is that they don't achieve the ideals that
might be expected in other situations (as quoted in the previous response).

Whether or not the bulbs will last in such a small reflector with an opaque
coating (not allowing the IR energy to pass through) is another question you
would need to consider if you pursued getting your own reflectors made.
Avoiding potential heat problems may be the reason why all of the existing
MR-16's are done the way they are.

Mark Jongewaard,
Lighting Technologies, Inc.