Imalent        
Results 1 to 11 of 11

Thread: "Frosted" vs clear projector lens?

  1. #1

    Default "Frosted" vs clear projector lens?

    I did a search but came up empty on the subject of "frosted" and clear projector lens. I'm curious as to the purpose of a translucent lens on a projector.

    The only site I found that touches on this subject is The Retrofit Source, but I'm a bit wary of their "information."

    Any comments? Is their information correct? What's the reasoning behind using translucent rather than clear lens? I'm guessing it has something to do with glare and light distribution...can anyone expound on that, if I'm correct? Is a clear lens a legal upgrade?

    https://www.theretrofitsource.com/bl...-clear-lenses/

    Most OEM projectors out there come standard with what is known as “fresnel” lenses. These projector lenses have circular lines molded into their surface, and are often produced with less than optically clear glass. So what? Well the fresnel lines and frosted/ translucent glass dim the output and soften the beam pattern so the projectors aren’t performing to their full potential. A true clear lens will help maximize the performance of the projector compared to the “detuned” stock lenses. Think of a projector just like any other original part on your car, of course there will always be an aftermarket performance/aesthetic upgrade available. Why doesn’t the car come with the most free flowing exhaust from the factory? Why aren’t the throw’s in the transmission shorter? The brakes stronger? The headlights brighter?

    Note that very few cars in the US domestic market come from the factory with clear lenses mounted on the projectors used inside their headlights; European vehicles are spec’d with clear lenses much more often. In fact, when retrofitting headlights started gaining in popularity several years ago, it was usually only possible to obtain clear lenses for a upgrade swap from “ECE” (Euro spec) headlights. (Thanks DOT!) Now, TRS offers a full line of 2.5″ and 3″ optically clear projector lenses for most projectors on the market. So whether you’re looking to enhance the output on the units you’ll be retrofitting, or the detuned factory projectors in your higher-end vehicle, we likely have an upgrade for your application.

  2. #2
    Moderator Alaric Darconville's Avatar
    Join Date
    Sep 2001
    Location
    Stillwater, America
    Posts
    4,544

    Default Re: "Frosted" vs clear projector lens?

    Fresnel lenses are used to save weight and material; you may have seen them in credit card sizes for a wallet magnifying lens. Lighthouses use them because traditional lens with the desired focal length would be prohibitively heavy.

    If it's part of the original design, then the manufacturer (ostensibly) knows what they are doing. The lens may have further modifications to it that are not immediately apparent (for example, a cylindric adjustment or multiple focal lengths) ; TRS' "clear" lenses may be completely wrong for the application. Changing the lens would surely ruin the performance of the lamp.

  3. #3

    Default Re: "Frosted" vs clear projector lens?

    TRS is wrong; fresnel lenses are not generally used in projector headlamps. There are projector lenses with a wide variety of patterns in the glass. Might be concentric rings (that doesn't make them fresnels!), might be various kinds of stippling, might be a partial or overall frosted texture. The purposes are to smooth out bright or dark artifacts in the beam, to reduce the cutoff gradient, and to control chromatic aberration (color fringe) at the top of the beam. Outfits like TRS, catering to idiots who think headlamps are fashion/style accessories, gobble up the BS about how sharper and sharper = better and better (false!) and textured lenses are "detuned" (false!) and reduce/dim the output (false!). These kinds of idiots spend money hand over fist to increase (worsen) the chromatic aberration because they think a blue or purple fringe is phat sick dope, yo.

  4. #4

    Default Re: "Frosted" vs clear projector lens?

    Quote Originally Posted by -Virgil- View Post
    chromatic aberration
    I hear this term a lot with regard to camera lenses. A lot of CA is bad. CA can be mitigated in software, but it's generally held that better photographic lenses don't need software CA correction.

    Now, does CA have any practical effect on driving?

  5. #5
    Moderator Alaric Darconville's Avatar
    Join Date
    Sep 2001
    Location
    Stillwater, America
    Posts
    4,544

    Default Re: "Frosted" vs clear projector lens?

    Quote Originally Posted by Ls400 View Post
    Now, does CA have any practical effect on driving?
    Chromatic aberration being, at its core, a focus problem, it sure does. When the components of white light do not focus correctly, the end result is a beam pattern that isn't quite right. Throw of the beam is affected.

    Then there's the other aspect, the color fringe. Probably some TRS fanboy would LOVE projecting rainbows everywhere, but that's not wise or safe (and could also land them in hot water for displaying red or blue light).

    Again, the manufacturer designed the complete lamp assembly, including a lens (Fresnel, aspheric, compound, frosted, unfrosted...). It works the way THEY made it. Dropping in the wrong lens (like a lens-shaped toy from TRS) is like popping out a lens from Grampa's bifocals and putting in a single vision lens- with the wrong diopter, even. Not wise.
    Last edited by Alaric Darconville; 10-05-2018 at 02:07 PM.

  6. #6

    Default Re: "Frosted" vs clear projector lens?

    Quote Originally Posted by Ls400 View Post
    does CA have any practical effect on driving?
    Headlamps are required to emit white light. Unofficially some allowance is made for minor color fringe, but a big deep-blue band above the cutoff means the lamp is emitting blue light. This makes the headlamp noncompliant and creates safety threats in traffic: bright blue flashes tend to make drivers do sudden things because they think "Oh, crap, it's the cops", and tend to make cops want to write tickets because only emergency vehicles are allowed to display blue light, let alone blue light that appears to flash.

    Also, in these nincompoops' crazed zeal for a razor-sharp cutoff with a blue fringe, they completely disregard (don't know/don't care) about the light distribution under the cutoff, which can be significantly altered by putting on a lens other than the intended one.

    Also, breaking open the headlamps to monkey around with the projectors causes all kinds of problems: water and dirt entry (very difficult to attain a good or lasting seal once the headlamps have been broken open, no matter how much "sealing compound" they might buy from TRS), wrong beam alignment (high beam relative to low beam), etc.
    Last edited by -Virgil-; 10-05-2018 at 06:50 PM.

  7. #7

    Default Re: "Frosted" vs clear projector lens?

    Quote Originally Posted by -Virgil- View Post

    Also, breaking open the headlamps to monkey around with the projectors causes all kinds of problems: water and dirt entry (very difficult to attain a good or lasting seal once the headlamps have been broken open, no matter how much "sealing compound" they might buy from TRS), wrong beam alignment (high beam relative to low beam), etc.
    Does this have anything to do with many recent headlamps being sealed with "permaseal"? It used to be that many headlights could be baked apart at about 200 degrees F, according to TRS. Now, many headlights aren't sealed with mod-friendly butyl rubber. Is this a deliberate design decision against retrofitters? Were butyl rubber sealed headlights prone to being baked apart in hot engine compartments?
    Last edited by Ls400; 10-05-2018 at 10:31 PM.

  8. #8
    *Flashaholic* idleprocess's Avatar
    Join Date
    Feb 2004
    Location
    dfw.tx.us
    Posts
    5,176

    Default Re: "Frosted" vs clear projector lens?

    Quote Originally Posted by Ls400 View Post
    Does this have anything to do with many recent headlamps being sealed with "permaseal"? It used to be that many headlights could be baked apart at about 200 degrees F, according to TRS. Now, many headlights aren't sealed with mod-friendly butyl rubber. Is this a deliberate design decision against retrofitters? Were butyl rubber sealed headlights prone to being baked apart in hot engine compartments?
    The "retrofit" market almost certainly isn't of any real interest to the OEMs. They design their parts around cost, performance, ease-of-installation concerns. The choice of one adhesive over the other likely due to performance or cost concerns; the more tenacious adhesive likely performs better for some designs or minimizes warranty issues.
    I apologize that this letter is so long; I did not have time to write a short letter

  9. #9

    Default Re: "Frosted" vs clear projector lens?

    idleprocess is right about the adhesive selection criteria. Headlamps have been sealed with single-use hot melts, with epoxies, with urethanes and with a variety of other substances for many years. That doesn't really matter to the question in this thread; baking a headlamp at 200 degrees causes damage and problems on its own, even before it's opened/ruined.

    Another reason for a projector lens to have some texture on it is to provide uplight for road signs. Retroreflection only happens if there's light to retroreflect, and contrary to the previously-mentioned idiots' sneering, ignorant babble about "squirrel finders", that uplight is important for safety. Those signs are there for a good reason, and drivers have to be able to read them clearly and at a long enough distance to take appropriate action, or else they wind up doing unsafe maneuvers because they don't see/can't read the sign until the last minute. It doesn't take a whole lot of light to light the signs, but there does have to be enough to do the job. Also contrary to common mythology, the US and UN ("ECE", "European", "E-code") headlamp standards both require about the same amount of uplight from the low beam. The UN standard actually requires slightly more/higher minimum. But the US standard allows a lot more (higher maximum).

  10. #10

    Default Re: "Frosted" vs clear projector lens?

    Quote Originally Posted by Alaric Darconville View Post
    Chromatic aberration being, at its core, a focus problem, it sure does. When the components of white light do not focus correctly, the end result is a beam pattern that isn't quite right. Throw of the beam is affected.
    CA indicates a focus problem, got it. Does a lack of CA therefore indicate correct focus, and thereby indicate that a bulb/light source/LED chip is a match for the optics? Or is there more to focus than just a lack of CA--can something be poorly focused, but not exhibit much CA?

  11. #11

    Default Re: "Frosted" vs clear projector lens?

    Quote Originally Posted by Ls400 View Post
    CA indicates a focus problem, got it.
    Chromatic aberration is not really a focus problem in the sense that most of us think of the word "focus". It's an effect arising from the physics of light. If you want to learn about chromatic aberration as applicable in projector headlamps, this is a very worthwhile purchase. A portion of its text:

    "Color Fringe in the Cutoff Line: Sharp cutoff contrasts are not projected color-neutrally by simple lenses. Instead, there are color fringes. This is due to the chromatic
    lens aberration which cannot be completely corrected with single lenses. Here, the red picture point is further away from the cutting plane of the lens, and the blue picture point is closer to it. What are striking and disturbing here are not so much the color effects of the cutoff line area on the roadway from the point of view of
    the driver, although that can be seen in extreme cases. Much more striking are the colors from the point of view of the oncoming driver when the cutoff line with its color spectra is at his eye level. Depending on the direction of sight and the observation distance, the light coming from the front opening of the headlamp appears
    yellow-red, purple, or blue-green. Because the two headlamps are generally adjusted somewhat differently, the oncomer sees the bright areas of the headlamp as different in color, or with one side neutral in color while the other is colored. Figure 9 shows what colorations arise at different distances and eye positions. As an
    example, we have selected an observation level for the eye somewhat above the axis at the distance G (focussing distance for the wavelength
    yellow-green). The eye then sees the light coming out of the lens as red to green at the top, green to blue at the bottom, which
    blends to a purple coloration. If the eye is further away in the axis at R, the light coming out appears red, above the axis blue-green,
    etc. etc. None of this can be reconciled with the demand for standardized signal images. The development of headlamp lenses must therefore be given the
    goal of preventing color effects to a large extent (...) On lenses that do not have adequate color correction,
    there is a dependence between the sharpness of the cutoff line and the color fringe. If the cutoff line is sharp, the color
    fringe is most likely to be blue to purple."

    Keep in mind this text was written in the mid-1980s when the only light sources contemplated were halogen.


    Does a lack of CA therefore indicate correct focus
    No.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •