Tail light brightness (bulb wattage)

Discussion in 'Workshop Forum' started by dcioccarelli, Dec 1, 2019.

  1. Hi all,

    I just wanted to confirm that the correct bulb for the tail lights is indeed the (smaller) 5W bulb (with a BA15S connector) and NOT the larger 21W bulb (used for the brake lights)? See below (5W bulb on the left).


    I'd never noticed, and just recently realised that I have the same bulbs installed for both the tail lights and brake lights. I can't be the only one, however, as after disassembling some of my spare tail light assemblies (of which I have many ), they also configured in the same way. The tail light itself does stipulate 5W:


    The reason I ask (other than curiosity) is that I'm attempting to make some LED tail lights (using COB panels rather than replacement bulbs, as I'm not impressed how these work). It is important that, on one hand, the tail lights are bright enough but, on the other, not so bright that the difference between the overall brightness of the tail lights and the brake lights is too small (i.e. so people didn't notice the brake lights).

    I'm currently experimenting with a configuration that uses 3 COB panels: two are used at reduced brightness for the tail lights:


    ... and all three are used at full brightness for the brake lights:


    I also took the opportunity to swap the orientation so that the brake light is the uppermost light (not the lower light as per the standard configuration). I think this is safer these days as modern are so high.

    The reason for the brightness question is that I'm empirically setting the tail light brightness by comparing to a tail light with a normal (incandescent) bulb. During the testing, I realised that the housing I was using had a 21W bulb installed for the tail light.

    I wonder how many other people are doing the same? That said, even when running 21W bulbs for both tail lights and brake lights, there is still a noticeable difference when the brake light is illuminated thanks to the way the reflectors are set up. Also, a 5W bulb does seem a bit weak these days, where most modern cars use LED tail lights which do seem to be much brighter overall.

    Thanks for any input!

    Last edited: Dec 1, 2019
    davejake likes this.
  2. toddr124

    toddr124 Hagerstown, MD

    Hagerstown, MD
    You want bright lights? Try using LEDs. Super bright tail and brake lights. There are some that are direct fit. Only blinkers are hard to change. You need a new blinker unit.
  3. dragonsgate

    dragonsgate True Classic

    My first LED's were similar to what you are doing. At the time there was not many choices so made my own boards.
    It wasn't too long after I got the tail lights project finished replacement bulbs were showing up on the market and I discovered Superbright LED's
    With Super bright I eventually got all the lights on my X except head lights converted to LED.
    In my opinion the replacement LED's are adequate but nowhere near what you have.

    After I finished switching the lights on the X I started on my 1970 FJ40.
    I didn't like the looks of the 1157 replacement on the front park/turn lights so adapted the panel type.
    I used the LED flasher on the Toy but like the hyper flash on the X19.
    From what I read, DOT set the flash speed for cars from 60 to 160 flashes per minute.
    The X lights flash at 140 with out the special flasher.
    johnnyx likes this.
  4. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Dom, I like the panel LED's you are making. I purchased the regular LED direct replacement bulbs for mine, but the car is still under construction so I haven't tried them. However I get what you are saying about the difference between those and the full panels.

    As for the wattage and brightness. I think the additional lighted area of the brake light when illuminated makes a significant difference in appearance (to motorists behind you). Personally if I were to retain incandescent bulbs, I'd put the 21W ones in all locations. To me that is more light to be seen from behind, and as stated when the extra segment for the brake light is illuminated it is very apparent. I think it's more of a relative difference in the rear lighting in general than a increase in brightness for any one bulb over the next. So I'd do the same with your LED's; use the same LED panels for every section of the housing.

    As for how the three segments are wired; one tail and two brake, or two tail and one brake. I have the same question for the custom tail lights going on my modified VW truck. It has three bulbs/segments in the housing, and some are two-way (dual element) bulbs but not all three. Furthermore the sockets can easily be swapped around and I have extra two-way sockets. So if I install all three as two-way bulbs, I could do any combination of the six outputs. All three bulbs light up in the "low" position for tail lights and all three in the "high" position for brakes (three and three). Or two and four, or whatever. I keep going back and forth on my thoughts. But the point I want to make is you can build your LED panels with two level diodes; low and high brightness two-way panels for each section. Then you can arrange them any way you want. Maybe all three are light up in the low position for tail lights, and all three on bright level for brakes (I think that's how I'll do my VW).

    Please show us how you are making these LED panels.
  5. Hi Jeff,

    thanks for the comprehensive reply! Yes, increasing the brightness of the tail lights isn't an issue with the incandescent setup, but with the LED panels the need to clearly demarcate the tail lights from the brake lights is more necessary. That said, these days with daytime running lights and automatic headlights, you wouldn't believe how many people I see driving with no rear lighting in heavy fog (as they are used to the car controlling the lighting for them), but I digress....

    I'm using the following 12V COB LED panels:


    COB panel.png

    The circuit is currently as follows:


    D1 and D2 represent the lower COB panels which run at reduced brightness for tail lights. The brake light applies full power to all three panels. This is just a prototype though: the use of a resistor to reduce the brightness is not ideal and will be replaced with a PWM based dimmer. There is also a 0.7v drop across the diode meaning that the bottom two panels are still slightly dimmer than the top one when the brake signal is applied.

    Overall, I find the look significantly better than trying to use a LED replacement for the standard globe (due to the directional nature of LEDs being incompatible with systems designed for filament bulbs).

    kmead, autox19 and Dr.Jeff like this.
  6. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    I like the dual brightness for the two tail lights, plus the third one for brakes. I know they make dual brightness LEDs, but not sure how they are designed.
  7. kmead

    kmead Old enough to know better

    Are you using red panels? If you use red, the other spectrums of light are not wasted in the lens. You will get better red (or amber for the turn signals) if you use a red LED system.

    An interesting look with the LED COB plates. That isn’t meant as a criticism.

    Have you considered 12v strip lights with 140°lens as a strip around the inside circumference of the housing to use the reflector assembly effectively? I know a totally different approach to the problem.
  8. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Karl, I'm intrigued. Can you give a little more detail, or better yet a photo that represents how that is done? I'm having a difficult time imagining exactly what you mean. Thanks.

    And while I'm asking for pics, Dom do you have one of the LED panels mounted in the housings (without the lens)? I have a good idea how you are doing it, just want to see a pic for added detail. Thanks.

    I agree with Dom and Karl that to use LED's with a traditional reflector/lens light housing assembly, something needs to be done to improve the light disbursement or pattern.

    P.S. Good to hear from you Karl. I know you have your hands full, just miss your presence here.
  9. rachaeljf

    rachaeljf True Classic

    Northampton UK
    I do like the look of these COB panels. The 100 ohm resistor is good as it reduces the brightness to a "legal" level. I believe modern cars do use PWM to alter the brightness of the rear/brake lights. There is more than demarcation between marker and brake lights to consider. The law in the UK limits the wattage of side (marker) lights and requires diffused lenses so that they don't dazzle following drivers. Brake and rear fog lights are higher wattage and focussed to more of a rearward pointing beam to attract following drivers' attention when they light up. Having what is in effect a permanently on brake light would be illegal on this side of the pond.
  10. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    I'm not sure what laws we may have here regarding bulb brightness. We tend to be very far behind Europe in such matters of public concern. But I've seen several models of new cars here with LED taillights (not brake lights) that are extremely blinding at night. While annoying, I have to admit you can't miss them and will likely be much less prone to getting rear-ended. For a tiny car like the X I'd be inclined to use the brightest lights I could get away with. Not that I want to annoy others (that just seems to come natural for me :oops:), but I'd rather piss off a few people and stay alive to make everyone happy and be dead.
  11. Hi Jeff,

    here you go. As you can see, it is kind of "plug and play", so the tail lights can be reverted at any time.

    rachaeljf likes this.
  12. Hi Rachael,

    indeed. And I can assure you that if it is illegal in the UK then it will be really illegal in Germany :(. This is why I was attempting to adjust the brightness of the tail lights to be roughly the same as the standard ones. Which brings back the original question in the post ;): is everyone running 21W globes instead of 5W globes in their (standard) tail lights? I have never seen the smaller 5W globes in an X1/9 tail light assembly, although apparently that is what is called for.

  13. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Dom, I need to actually look to see what bulbs are in any of my tail lights - I don't know. All of my X's are stripped down for body restoration work, so I'll have to dig the light assemblies out of boxes. Honestly I'd forgotten you are in Germany, so my comments about bright American lights wasn't relevant - sorry.

    Thanks for the pic, now I see. I guess with that approach the reflectors and everything else can just remain in place behind these LED panels. Nice. ;)
  14. Hi Jeff,

    no stress.. the comments above were in reply to Rachael concerning the regulations in the UK about the permitted brightness in the UK. Many cars have very bright tail lights here as well (I don’t think the US is alone in this regard). This is why I’m concerned that if I aim for a similar brightness to a 5W bulb, it will be far too dim by modern standards. I wonder how they measure what constitutes a permissible brightness. Lux, but at what distance....
  15. rachaeljf

    rachaeljf True Classic

    Northampton UK
    Dom, I had a look at the UK lighting regs, which will no doubt align with European regs. It seems that the requirements for a rear marker light's size and wattage/intensity are free, all that is required is that the light is red, and does not dazzle following drivers. There are visibility angle requirements, 45° inwards, 80° outwards, 15° above and 10° below the horizontal. It does no harm to "underrun" the LEDs to lengthen their life, this is more relevant to the rear marker lights.
  16. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    With your impressive talent for electronic circuits, can you make them "adjustable" for brightness? Perhaps switchable for a few choices of output. Then you could play around with different conditions and determine what you like. I bet you could even make a remote controlled, continuously variable, automatic sensing, situation reactive, multi function light system out of it. ;)
    rachaeljf likes this.
  17. ArtBasement

    ArtBasement Erwin Timmers

    Like this?
    Dr.Jeff likes this.
  18. Dr.Jeff

    Dr.Jeff True Classic

    Sin City

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