How bright should a rear fog light be?

[Diesel_Bomber]

Most people want LED lighting *AND* for it to look like it was factory installed.

Picky picky!

 

[-Virgil-]

What unused turn signal filament in a Tacoma? I've seen "JDM'd" Civics and Subarus with a clear-lens aftermarket version of the red-lens European-market rear fog installed in the bumper fascia, and equipped with an amber bulb. Certainly bright and conspicuous, but also very dangerous because steady amber light means you are looking at the front of the vehicle.

I've seen standard truck/bus LED lamps placed behind (not cut into) the lens of vehicle lights intended for use with bulbs. It can actually work fine if the LED unit is mounted close to the rear face of the lens, and sometimes even if there's some space between the lens and the LED unit. The critical thing is getting the angle right; if the LED unit is tipped or tilted in any dimension, the light distribution won't be proper.

 

[iroc409]

What unused turn signal filament in a Tacoma?

2005+ Tacoma

I haven't pulled out the rear turn signal bulb, but I believe it is the same as the front unit--I think it's a 3157A (looks the same, anyway). Only one function, turn signal, so it's only wired to use one filament. Same with the front, turn signal or DRL, but only uses one filament.

I've seen people illuminate both filaments of the front bulb. For example, use the "unused" filament for their own DRL implementation and keep the factory signal function (trucks that came without DRL). All you have to do is pull the wire seal and insert the proper connector to your wiring to use the other filament.

It's probably easier to just use factory DRLs--they only are about $50 in parts, if you can do the install yourself.

 

[Alaric Darconville]

I've seen people illuminate both filaments of the front bulb. For example, use the "unused" filament for their own DRL implementation and keep the factory signal function (trucks that came without DRL). All you have to do is pull the wire seal and insert the proper connector to your wiring to use the other filament.

But the unused filament on a 3157 is the minor filament, only 22.6 lumens. Not enough to satisfy the DRL requirement (if it did, it'd be too bright to be a marker/parking lamp, which is the typical minor filament function). (BTW-- it's a 4157 for the front turn signal, I don't have the lumens values for the major/minor filaments).

This is the problem with so many home-grown "solutions"; they either do not resolve the perceived problem, or they create problems of their own.

It's probably easier to just use factory DRLs--they only are about $50 in parts, if you can do the install yourself.

Safer, too. Not to mention that you open yourself up to a lot of liability with non-compliant DRL implementations; factory DRLs would be compliant.

 

[-Virgil-]

4157 has same performance characteristics as 3157. Difference is longer lifespan for 4157.

 

[Diesel_Bomber]

I was looking for something to mount in the gap between the tailgate and bumper on my truck. Although I figure my chances are slim, otherwise I'm stuck cutting up the bumper or mounting something on the bottom of the bumper.

Take a look at this. Regulatory compliant stop/turn/tail light in a package 1.3" wide. Legal to mount horizontal, vertical, or at 45 degree angle. As our resident expert has stated that rear fogs are photometrically identical to brake lights, the stop function of that lamp should do what you want, if 1.3" is thin enough.

 

[Alaric Darconville]

So, looks like the stuff in the "try me" packaging was Blazer, not PM. My mistake!

 

[-Virgil-]

The photometric requirements are identical, at least on axis, but that does not mean that rear fog lamps and stop lamps themselves perform identically. Mostly they don't; most rear fogs have higher axial intensity for the distance "punch" you need through fog. Also it helps maintain conspicuity of the stop lamps when the rear fogs don't look identical. For those reasons I don't recommend using a stop lamp as a rear fog, but if you must, it's probably better than nothing. Leave lots of distance between it and your stop lamp, and try to set the vehicle up with amber rather than red turn signals to avoid lumping too many functions on a red-light appearance.

 

[Alaric Darconville]

The photometric requirements are identical, at least on axis, but that does not mean that rear fog lamps and stop lamps themselves perform identically. Mostly they don't; most rear fogs have higher axial intensity for the distance "punch" you need through fog. Also it helps maintain conspicuity of the stop lamps when the rear fogs don't look identical. For those reasons I don't recommend using a stop lamp as a rear fog, but if you must, it's probably better than nothing. Leave lots of distance between it and your stop lamp, and try to set the vehicle up with amber rather than red turn signals to avoid lumping too many functions on a red-light appearance.

So, even a separate "brake light LED module" isn't going to cut it. Sure, it'll look different from the factory brake lamps, but that intense punch is needed, because sometimes it's hard to see the vehicle ahead even when they are braking. Also, a proper rear fog lamp kit may come with the lighted warning switch and all that, too.

 

[Diesel_Bomber]

The photometric requirements are identical, at least on axis, but that does not mean that rear fog lamps and stop lamps themselves perform identically. Mostly they don't; most rear fogs have higher axial intensity for the distance "punch" you need through fog. Also it helps maintain conspicuity of the stop lamps when the rear fogs don't look identical. For those reasons I don't recommend using a stop lamp as a rear fog, but if you must, it's probably better than nothing. Leave lots of distance between it and your stop lamp, and try to set the vehicle up with amber rather than red turn signals to avoid lumping too many functions on a red-light appearance.

Making sure I understand this correctly. A photometrically compliant/legal brake light is a photometrically compliant/legal rear fog light, it's just not an ideal implementation of a rear fog light? Similar to an old sealed beam headlight that is a photometrically compliant/legal headlight, just not an ideal implementation of a headlight?

 

[-Virgil-]

Whoops, looks as if I was recalling an older version of the SAE spec (J1319) for rear fog lamps. The photometric requirement is compatible but not the same for rear fogs and for stop lamps. The photometric requirements are practically identical for US and ECE rear fogs, just expressed differently due to different test voltages.

US stop (brake) light size 1, e.g., a single-compartment lamp with a filament bulb: Minimum 80cd at (H,V) and (H, 5L/5R); min 40cd at (H, 10L/10R); min 70cd at (5U/5D, V); min 30cd at (5U/5D, 10L/10R); min 10cd at (5U/5D, 20L/20R); maximum 300cd anywhere.

Rear fog light (at US test voltage): Minimum 125cd all along H line from 10° left to 10° right and all along V line from 5° up to 5° down, minimum 62.5cd within the diamond-shaped zone with corner points (H, 10L/10R) and (5U/5D, V). Maximum 250cd anywhere.

So the rear fog lamp has a slightly lower max intensity, but a higher minimum intensity at a larger range of test areas, while the stop lamp has a slightly higher max intensity, but a lower minimum enforced at more test points through a wider angular range.

 

[Diesel_Bomber]

I think I understand it. A single lamp can be made to be compliant with both brake light and rear fog light standards, but a lamp can be a compliant brake light without being a compliant rear fog, and vice versa.

Please disregard my previous suggestion of a brake light for use as a rear fog light.

 

[iroc409]

Thanks for the good information, Scheinwerfermann. I guess it could be possible to find a brake light then that meets the requirements of a fog light, but I would imagine it would be pretty difficult for Joe Sixpack to get the data you reference for a project.

I guess I'll just have to compare to available options and see what I can cobble up. The rear end of the truck is well set-up in my case: amber turn signals, and tail lights that would be fairly obviously different from anything I would probably mount. The center stop light is a different story, but it's on the top of the cab and likely far enough away to cause any confusion.

 

[fangle]

Very good thread. Thanks for the info.

First, a question. What elevation from the road is best for mounting a rear fog light? For a typical truck it could go below, in, or above the bumper, or on some other rear surface like a toolbox or bed rail. I'm guessing that on the roof would not be correct?

If you want to make the rear fog require turn on each time, you can use a single relay if you get a double pole device. Pulling power for the relay from an existing fog light circuit should be good. IF you have the front fogs on AND you press the button THEN the rear fogs come on until either you turn off the front fogs or turn off the car. Sounds like a typical motor control pushbutton start/stop circuit.
http://sub.allaboutcircuits.com/images/04176.png

 

[Ofelas]

Schein - would you recommend an amber or red rear fog bulb?
This is to replace my 921 rear cargo lamp bulb on my pickup.
Choice of LUKS 921 or LED?

 

[-Virgil-]

Schein - would you recommend an amber or red rear fog bulb?
This is to replace my 921 rear cargo lamp bulb on my pickup.
Choice of LUKS 921 or LED?

"None of the above". Your cargo light is nowhere near being a suitable rear fog lamp, no matter what bulb you install. If you want a rear fog lamp, install a rear fog lamp designed, manufactured, and certified/approved as such. Also, red is the only acceptable color for a rear fog lamp.

 

[irsa76]

I think I understand it. A single lamp can be made to be compliant with both brake light and rear fog light standards, but a lamp can be a compliant brake light without being a compliant rear fog, and vice versa.

Please disregard my previous suggestion of a brake light for use as a rear fog light.

Correct, a rear foglight can comply as a brake light, but a brake light may not comply as a foglight.

And to clarify the early posts about mounting, a single foglight can be mounted in the center OR, ideally, on the driver's side. I can't put my hands on the actual dimensional location requirements other then there are strict height restrictions in regards to mounting locations. Which is why on SUVs with height adjustable suspension, Range Rover, VW Touareg, Audi Q7 etal, the rear foglight automatically switches OFF when the suspension is set to high clearance mode. Further to that, on my Citroen the rear foglights are disabled when a trailer/bike rack is plugged into the trailer socket.

 

[-Virgil-]

Correct, a rear foglight can comply as a brake light, but a brake light can not comply as a foglight.

There's a lot of overlap between a UN/US rear fog lamp and a US stop (brake) light, and there's some overlap between a UN/US rear fog lamp and a UN stop (brake) light, which means a single lamp could qualify as either/both/all three.

 

[irsa76]

There's a lot of overlap between a UN/US rear fog lamp and a US stop (brake) light, and there's some overlap between a UN/US rear fog lamp and a UN stop (brake) light, which means a single lamp could qualify as either/both/all three.

I corrected my post. I do recall seeing a note in an old Hella Australia listing that their brake lights are NOT ECE approved as foglights, however they make special mention that the fog light function in a couple of their truck/trailer light assemblies ARE approved as brake lights, indeed they are actually rewired internally in Australia so the fog light functions as a brake light, with no fog light function.

 

[Ofelas]

"None of the above". Your cargo light is nowhere near being a suitable rear fog lamp, no matter what bulb you install. If you want a rear fog lamp, install a rear fog lamp designed, manufactured, and certified/approved as such. Also, red is the only acceptable color for a rear fog lamp.

Understood.
Would it be legal to replace my cargo lamp with a tail lamp/third brake lamp with the appropriate socket + dual filament red bulb?