Why are Surefire reflectors rough?

I thought I'd make this a new topic even though its related to another recent post.

When I compare the Surefire reflectors to other reflectors (like the Stealthlite 4AA), they are rough. The Stealthlite 4AA is actually quite smooth.

At first one might think that a perfectly smooth reflector would be the best. But it seems this is not the case, judging by the excellent beam made by both my E2 and 9P.

Does this produce smoother edges on the brightest central part of the beam and help to remove rings?

Another question I've had for a long time is how is a slightly rough reflector made? Sand blasting? Chrome plating?

Or perhaps the slight roughness is just a feature of chrome plated Al?

Your comments are welcome.

Sean

Pwell. I also came up with this brilliant observation. The good people at CPF set me straight. We are NOT the first to find this. (Hope is eternal). The reflector is what I call orange peel. Surefire calls it something else(?). I sure wish other companys would use it. Seems to me that it does cut out dark rings.
....dana....

The rough coating is called "stippling", and in SF's case it's done by metal vapor deposition of the reflector. (it's mentioned on the box that the light comes in)

While I do not know what variant of the process SF uses, the most common form of metallic vapor deposition is by placing a sacrificial filament of the desired metal in a vacuum chamber and passing a very high current of electricity through it.

At the correct temperature, the filamnet will boil. (All things will boil at certain temperatures and pressures, metal is no exception.)

The filament material evaporates and is then deposited onto the target. Stippling can be created by varying such process parameters
as pressure, the species of gas that is introduced into the vacuum chamber after the atomosphere is removed, and applying another current to the target to be coated.

There are other methods for vapor deposition
also, I don't know which one SF uses. The stippling "smooths" the beam before it is collected at the focal point of the reflector. Think of the stippling as many additional tiny reflectors that smooth the beam.

MVD is more involved than this, I'm only giving the basics here, but I hope it helps.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>At first one might think that a perfectly smooth reflector would be the best. But it seems this is not the case, judging by the excellent beam made by both my E2 and 9P.

Does this produce smoother edges on the brightest central part of the beam and help to remove rings? <HR></BLOCKQUOTE>

Yes, you are quite correct in your assumption. The "roughed up" reflector surface prevents the appearance of fine rings - the same way a faceted reflector does. A smooth reflector can be thought of as a curved mirror - the curved reflection of the filament in the bulb itself creates a circular line or ring in the beam.

A texturized or faceted reflector will not reflect in this manner, instead creating lots of little tiny reflections of the filament that overlap - resulting in the appearance of a smooth circle of light.

Even Eveready has figured this out as seen in their "Superbright" el cheapo line of household lights (about $3 ea.) - the reflector is 1/2 faceted (near the bulb) to create a smoother beam. Sam's Choice WalMart brand cheapie lights (about $5) have fully faceted reflectors. Not many other brands use this simple technology to smooth out the beam, and the results can be very nice (as you can see in the Surefires).

Eveready even makes a headlamp with the 1/2 faceting that is FOCUSABLE - this is the first time I have ever heard of faceting used in a focusable lamp - I'm very curious as to how well this works - it should do very nicely.

Maglight would be smart to facet or texturize their reflectors as well - good lights, but poor beam quality.

EDIT: Gman: Your post wasn't there a second ago. You're too quick for me! Sorry for the overlap.

Really, the smooth reflector gives a spot or "focused" beam and the dimpled reflector is creates a wider beam. Most Focusable flashlights have a smooth reflector so that they can have a better spot beam where needed. An example is the Princeton Surge against the Ultrastinger. The Surge beam is wider (it is focusable btw) than the Ultrastinger - in focused position on both, the Ultrastingers beam is much tighter than the Surge at distance. The dimples make the beam wider, and also makes for a better beam in the wide focus position.

In the end, smooth reflector is better for spot and dimple is better beam in wide (which is when the spider wens come out.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by pwell:
At first one might think that a perfectly smooth reflector would be the best.<HR></BLOCKQUOTE>

The reason is simple: If you have a perfect point light source, a smooth reflector will do the job perfectly. But when the light source (the filament) is large in relation to the reflector you will get an unpleasant light distribution.
Good spot light reflectors are usually larger in relation to the filament, so a smooth one will bring acceptable results.

Wow, thanks for the great responses from everyone.

The process of metal vapour deposition is also used in the manufacture of semiconductors, which I'm kind of familiar with. So I understand what you are talking about. If one where to make their own "stippling" the most expensive part would be a vacuum I suppose.

Vacuums are also used by Amateur rocket people who make their own rocket propellants, and there have been a lot of inovations by individuals to make them cheap. It would be intersting to see the relationship between the level of stippling and the amount of smoothing of the beam.

I guess we can say that "faceting" is like stippling, except that each of the discreet reflectors are much bigger.

I guess Surefire have fine tunned their level of stippling. Maybe they have patented it. I know they have even patented some flashlights.

Sean