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Can anyone explain the dark zone?

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  • Can anyone explain the dark zone?

    So, can anyone explain to why these aftermarket projectors (no matter how I place the bulbs/shim in the projector) creates a dark spot when the projectors overlap. To my recollection, the highest point of the slope should go right across without any change of intensity but from what I have seen in my setup and all over across the net that the DS projector tends to be "dimmer" than the PS so it never blends in together and leaves a "dark spot" right in the middle.

    You can see these images also on TRS that it's not a misplacement of the hotspot because they're technically the professionals on this... seems to be a norm that everyone over looks. It bothers me till this day unfortunately, and I don't want to put the low arc from the PS lined up with the high arc of the DS... I tried it once and it felt too high...


    Believe me, I'm not complaining on the total light output, I'm happy with that, just wanted to see if there was some sort of explanation why this occurs on these projectors and not OEM.

    Here are some examples from my car.




    ...and this is from the net...


    even though this dude says even brightness it's mainly below and not at the cutoff.... dunno, this is probably just me wanting perfection. LMK please.

  • #2
    Its normal. The reason for this is there is decline in illumination along the cutoff as it extends outward to the right. This would not be as noticeable if you only had one projector, obviously, but because it blends into the right side projector, there is an abrupt increase in light, making it more obvious to the eye. This will always be the case. Its just that in some images on the internet, some lamps have more light along the edge than others making it LESS noticeable. Or too much camera exposure will hide that dead spot.

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    • #3
      H1 projectors?

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      • #4
        Originally posted by evo77 View Post
        Its normal. The reason for this is there is decline in illumination along the cutoff as it extends outward to the right. This would not be as noticeable if you only had one projector, obviously, but because it blends into the right side projector, there is an abrupt increase in light, making it more obvious to the eye. This will always be the case. Its just that in some images on the internet, some lamps have more light along the edge than others making it LESS noticeable. Or too much camera exposure will hide that dead spot.
        Thank you evo, just wanted to make sure this was normal. (An unfortunate normal)

        Originally posted by niZmO_Man View Post
        H1 projectors?
        Mini D2S 4.0 Projectors

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        • #5
          One thing to keep in mind, is that the beam pattern "radiates" from the projector outwards. If the beam is designed to maintain intensity along that "dark zone", it also means that the projector would be expending a lot of its limited light to the side and less to the lane straight ahead.

          If you look at isolux patterns (example here courtesy of rallylights), a low beam needs to have high enough intensity near the hotspot (around dead center) to be able to reach that far (to the right of the illustration).



          If the design eliminates the dark zone, then, the isolux might look more like a foglight pattern:


          With the same light source, this means a weaker hotspot, and shorter distance reach. It means at freeway speed, you won't be able to see objects ahead as early as you would with the low beam pattern before.

          To make things worse, because low beams must also not blind oncoming traffic, the solution in current day projectors is to introduce a low beam shield. This blocks off light that would have been directed towards oncoming traffic. That is why the first isolux above (for RHT, or commonly LHD) has a lower reach on the left side of the road. If the design expends more energy to fill this "dark zone", for a left-right symmetrical reflector bowl (and generally radially symmetrical lens), this means that there is also extra light directed in a region that is blocked by the shield. That would reduce its total output. Conversely, the unit will need brighter bulbs to compensate for the higher fractional loss.
          Jul 2012 ROTM (3-way quad headlight) ; Sep 2015 ROTM (custom muli-lens 7" fogs)

          3-way quad wiring; foreground limiter; squirrel finder;

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          • #6
            I do understand as to why a LHD vehicle will produce more light towards the right side of the road more so from the left side. Mainly to not blind oncoming traffic and to illuminate the right shoulder for pedestrians/curbs/signs and it's the furthest area away from the drivers where they cannot see properly. I recently checked out a YouTube link evo had in his sig which stated that it is good to have something similar in that dark zone so the slower vehicle you might have in front of you doesn't get blind either. Being that technology is progressing to a more automatic motorized style head lighting system where projectors move and image sensors are installed to view objects in front of the car so blinding becomes a thing of the past.

            Every now and then the so called dark zone/spot catches my eye on a car or wall and it does bother me that it's not a flat, evenly spread light source I do understand the possibilities of the design and safety that went into designing the type of pattern on these projectors, unlike OEM which virtually don't have that dark spotting. Obviously, if the hot spot is generating underneath the arced step and as it illuminates outward towards the edges while meeting the other projector and overlapping over it's hot spot you can drastically see the difference in intensity.

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            • #7
              Originally posted by }{yBr!D^ View Post
              Every now and then the so called dark zone/spot catches my eye on a car or wall and it does bother me that it's not a flat, evenly spread light source I do understand the possibilities of the design and safety that went into designing the type of pattern on these projectors, unlike OEM which virtually don't have that dark spotting.
              Both OE and a lot of the better aftermarket HID projectors employ the same functional design, in that the dual ellipsoid reflector bowl has multiple facets that optimize light distribution. For that area to not be dark, it means that the hotspot has to have a very strange and wide design that would use up a lot of the quota that would've been used towards the dead center area.

              The typically clearer aftermarket lens affects the distribution a little bit (relative to fresnel, dimpled, & other OE patterns on the lens), but will not materially change this.

              Here's an OE example, from a Ford Kuga in the UK. It happens to be halogen, but the general points above hold equally for halogen and HID -powered projectors. Note the dark spot is also there. I took these pictures in light of this thread.


              Jul 2012 ROTM (3-way quad headlight) ; Sep 2015 ROTM (custom muli-lens 7" fogs)

              3-way quad wiring; foreground limiter; squirrel finder;

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