LED Stop/Brake Lights - don't bother?

[MarekH]

Dear David,

For "battery terminal", you probably meant to write "alternator terminal", because at anything other than idle speed, it is your alternator which is powering the electrics in the car.

kind regards
Marek

[Heuer]

On an alternator with integrated regulator you could use either as they are directly connected together by a short heavy duty cable. On an alternator using the external regulator you would want to connect to the battery terminal otherwise you would end up with 20 volts+ at the bulbs which would indeed make them very bright but probably not for too long!

[MarekH]

David,

That makes no sense to me:- whether the alternator has an internal or external regulator is trivial, as the regulator will function such that the B+ terminal of the alternator is at the desired regulated voltage at all times. Since the B+ terminal of the alternator is directly connected to the battery via a very thick cable, it is not conceivable that one end of this cable is at 20v and the other at 14v (or battery voltage at very low rpm). My only point is that that thick cable has a non zero resistance and will have a voltage drop along it as it is carrying a heavy current. Thus you maximise light output by connecting your light feed at the alternator rather than the battery. Some clever people put their alternator output sense wire at the battery and thus make sure that the regulator regulates to account for any voltage drop along this heavy cable. NO etype was ever supplied with an integrated (single wire) alternator and ALL of them have a direct connection from the alternator to the battery.

kind regards
Marek

[PeterCrespin]

LED's also dim with a reduction in voltage. If you want to use an LED bulb to replace a stop bulb you need one with at least 460 lumens to equal tungsten filament. If you want brighter than tungsten you need even more lumens and the LED's must be the same colour as the lens (red in this case). Current LED's are only about 40% efficient so if the manufacturer quotes 500 lumens you get 200 lumens. To prolong the life of high output LED's they need a heatsink.

This is where crude empirical observations come in handy. We can skip all the number crunching because whether by accident or design, people's eyes and David Kerr's photos show beyond any shadow [geddit?) of doubt that LED boards are way brighter than lamps with a standard tungsten bulb. Plus calculated bulb outputs don't take into account dull /corroded tungsten reflectors, the bonus 'speed' of LED illumination and the low current draw which means voltage drop isn't a significant issue for LEDs, unlike 21W tungsten stop lamps. The one viable argument against the boards as supplied is cost. One person's expensive lighting is another person's cheap insurance. Everybody has to make up their own mind and there are as many subjectively 'right' answers as there are potential customers. I wouldn't bother for an S2 but for an S1 I might. For my D-type I probably will, since apart from visibility with even smaller lamps than S1 E-types, every reduced bit of drain is handy on a positive earth dynamo system running Le Mans headlights.

Pete

[Heuer]

Yes Pete, I understand your point, but my contention is the tungsten bulbs are only working at half their rated output because of the voltage drop at the socket. People seem to be addressing the effect with a quick fix rather than addressing the cause. Whilst LED's do dim with reduced voltage they do so at a lesser rate. So my theory, which I am about to put into practice for our collective knowledge, is running a dedicated high capacity feed to the rear lights will allow them to work at their rated capacity which, I hope, will make them equal to or brighter than the best LED's (the boards supplied by Classic Auto LED's Co). If you check out the photos I took of the headlight upgrade you can see how the dedicated power line practically doubled headlamp brightness. Parts will be here in the next couple of days so I will post the results. In the meantime please resist the temptation to bung LED's in the D-Type and consider concealing a couple of relay's to operate those Le Mans headlights or are you going to fit LED bulbs in there as well


Marek - you are of course right. I answered after we returned from our monthly village wine tasting at 11:25pm clearly having overcharged my batteries!

[PeterCrespin]

I got your point David and do look forward to what I know will be fully-documented results. You are the non-pareil of methodical experimentation and do everyone here a great service. A couple of points would be that as you know far better than I, voltage drop in car wiring only causes trouble when a significant current passes through the circuit. So whereas the rewards from headlamp relays are indeed worthwhile compared to old wiring, and there may turn out to be visible improvement for stop lamps too, the lower the current draw the lower the benefit of solving a decreasingly significant issue. So we know before you start that there will be far less visible boost for a 5W tail lamp bulb, even if a 21W stop lamp filament glows a bit brighter - but I am open minded and look forward to the results. Not only would LEDs never need a relay or cause voltage drop as they draw practically no current, they'd probably work equally well to the naked eye if there were only one or two strands of wire left. Plus all light goes direct through the lens without a scuzzy reflector. Of course, I'm arguing from contrary positions by suggesting that extra wires and sealed relays are unwelcome complexity and failure points, whilst advocating 'complex' LEDs over bulbs for anyone worried about daylight visibility.

More power to your elbow Sir, as well as your tail :-)

[PeterCrespin]

BTW, I haven't had my morning coffee yet, but wouldn't you need additional relays, one per side, to avoid voltage drop to the indicators if you wanted to go that route? So that would be four relays and four extra wire runs in total?

Pete

[Heuer]

Not bothering with indicators - they flash amber, they draw attention. Current draw does determine voltage drop of course (V=IR) and my calculations suggest the standard wiring results in a drop of 18% plus whatever resistance there is in contacts and connectors to a pair of 21W bulbs, which means about 10.8v output voltage from a 13.2V source. That in turn means a drop from 460 lumen's to about 200 lumen's in a tungsten bulb. The side lights are a different matter as they only draw 10W between them so I would expect the voltage to drop by only 6% which means they would be about 80% of their rated output.

As regards the current draw of LED's they suck up more than you think. I believe the LED boards consume about 7.5W each on brake so still capable of producing a 10% voltage drop. Not of real world relevance in the UK perhaps but those particular boards could be at the mercy of 'LED Meltdown' because of the lack of thermal dissipation (no heat sink's). Riding the brake pedal on a really hot day might not be a good idea.

[vrracing]

Ideally you want to maintain a constant voltage and amperage with LEDs and control brightness thru PWM and component selection. Underdriven LEDs will mostly just stop illuminating and overdriving doesnt increase output but does decrease lifespan (How is LED brightness related to current?). The light output doesnt vary significantly with V and I and it is really important to control I precisely.

Here is a cool wizard for designing LED arrays. Playing with it helps clarify a lot of LED design considerations.

One other interesting difference that has been noted in the thread is that LEDs are directional (by design, not physics) while tungstens are not. Lumens are measured as the total light output in all directions. Great for house lighting but in these use cases the light should be directional. We want to brake lights to shine backwards, not towards the front of the car. With a tungsten bulb you're getting maybe an eight to a quarter of the light energy naturally going in the direction you want, while the rest is going up, down, left right and backwards. It's the efficiency of the reflector that determines what percentage of total lumens is being put to good use. With a light meter it would be fairly easy to compare the light output of a 21w brake bulb hanging in air vs the same bulb mounted in an reflector (but no lens). Based on observation, I suspect the reflector is not very efficient so the net lumens delivered to the texting Camry driver barrelling towards the back of your freshly restored E-type is no where near 460 lumens.

Another aspect of the brake light use case is that it's red. The red lens filters out ultraviolet, blue, green, yellow and orange light allowing only the red to pass. That's why you only use red LEDs in brake lights because that way almost all the available light (within the efficiency and purity of the lens) passes thru. So a x lumen red LED will present almost x lumen to our Camry driver. Actual measurements would be really interesting to see how efficient the red lens is at letting the red LED light thru.

A tungsten bulb on the other hand produces white light spread across all the colors of the rainbow. But as noted all but the red gets filtered out (turned into heat within the lens?). Now at first one would think that only 1/7 (red being one of seven colors of the rainbow) of the tungsten lumens (65 lumens) would get thru and be put to work. But it turns out that tungsten output isn't evenly distributed across the visible spectrum and is biased towards the red end of the spectrum. This Popular Mechanics article maps the spectrums of different household bulbs but if you click on Larger View under the picture you'll see that the tungsten bulbs are very biased to the red and infrared of the spectrum. So it seems you should be more than 65 red lumens. Again measurements should tell the tale.

Another interesting factoid is that tungsten bulbs convert only 5% to 10% of the energy sent to them meaning only 1-2W of the energy sent to that brake light bulb are being used to get our texter to look up from their Blackberry. The rest is being wasted as heat embrittling and clouding the plastic in the red lens.

If someone has the LED conversions and is interested in taking some measurements, it turns out no special equipment is needed. There are light meter apps available for smart phones. There are many on the iPhone ranging from free to $10. Most are focused on setting ISOs but many show Lux. And I think the relative performance of the lighting options is what's interesting (i.e., 21w tungsten is 4.3 times brighter than the XKS LED brake lights at 20 meters).

This has been an interesting thread and I've enjoyed following along.

[Heuer]

Based on observation, I suspect the reflector is not very efficient so the net lumens delivered to the texting Camry driver barrelling towards the back of your freshly restored E-type is no where near 460 lumens.

Agreed, but the 460 lumen's refers to a new bulb under factory measurement conditions according to Bosch. The UK legislation is a maximum of 340 lumens taking account of real world conditions.

Should point out the legal implications here: Construction and Use legislation (UK and EU) says stop lamps must be rated between 7W and 21W (110 - 340 lumen's) so fitting more powerful LED boards can mean an MOT failure or being stopped by the Police. In the USA the acceptable range is 9W to 35W (80 - 552 lumen's) although flashing stop lights are currently illegal. Can you buy 35W stop lamps in the US?

Vehicles first used before 1 September 1965 may have direction indicators incorporated with stop lamps, or combined with front or rear position lamps, in which case front indicators may be white and rear indicators red. DaveK might therefore be OK in using the optional DRL/front indicators on his LED boards providing he changes the lenses to clear (US spec).

[Gfhug]

My LEDs finally arrived and have been fitted. Both the reverse lights and rear/brake lights certainly look a lot brighter in daylight, although the reverse doesn't show the difference in the accompanying photos. Looked much better at all angles, too, not just straight from the back.




So I would say these from Autobulbs are worth the cost and don't require any re-modelling of the light fittings or making up your own LEDs. As a reminder the rear/brake are: http://www.autobulbsdirect.co.uk/382-Su ... -Bulb.html (choose the red ones), and the festoon style reverse are: http://www.autobulbsdirect.co.uk/264-le ... white.html The latter fit the Elan rear lights, but they do have other bulbs for the standard E Type. Next, after some road miles, will be to try their amber indicator bulbs.

An idea might be for those who want front daylight running lights would be to fit LEDs in the side lights re-wired directly to the ignition switch or the sidelight switch, with the rear and headlights coming on together with the headlight switch? Just a thought.

Geoff

[Dave K]

DaveK might therefore be OK in using the optional DRL/front indicators on his LED boards providing he changes the lenses to clear (US spec).

Well I'm not doing that, they will stay as they are.

One thing to note is that the rear tail lamps are extremely bright at night almost like fog lamps. In the recent MOT when I had the LED's fitted the tester never mentioned how bright they were just that the brake lights once applied were instant rather than the slow to warm up tungsten lamps he has seen. LED's don't fail they just get dimmer over time I believe.

Dave

[Gfhug]

LED's don't fail they just get dimmer over time I believe.

Dave

At times I feel I must be an LED! :?

[Heuer]

One thing to note is that the rear tail lamps are extremely bright at night almost like fog lamps. In the recent MOT when I had the LED's fitted the tester never mentioned how bright they were just that the brake lights once applied were instant rather than the slow to warm up tungsten lamps he has seen.

Now that is a worry and asking to be pulled by the Police! I know several people who have been stopped for having their fog lights on unnecessarily. The maximum output for side lights under the Construction and Use Regulations is 5W specifically to prevent blinding other following drivers.

[Dave K]

If I ever get caught in fog I'll be alright :D

Dave

[PeterCrespin]

Now that is a worry and asking to be pulled by the Police! I know several people who have been stopped for having their fog lights on unnecessarily. The maximum output for side lights under the Construction and Use Regulations is 5W specifically to prevent blinding other following drivers.

No problem. The LED boards will be way under a Watt, I assume. The worry will be when the law is re-drafted in terms of lumens over ambient and all Plod traffic cars are equipped with light meters. I make that approximately the twelfth of never.

[Alberto]

Just a quick comment based on my experience. Many years ago I installed the relay set up with direct battery connection on the front headlights of a 1967 italian sports car I own. The difference was astonishing and transformed the car from something that I would not drive at night to one that I would make a point of driving at night. I cannot emphasize enough what a difference it made. My recommendation is to do this upgrade to every vintage vehicle that you intend to or want to drive at night.

If you did the same set up for the rear tail lights, there's not doubt that the improvement will be equally substantial and noticeable. I don't think you would need to go LED, frankly, unless you want the instant on feature of LED's.

Got my parts from here: http://www.danielsternlighting.com/ but that was many years ago. I don't know if he is still selling parts and giving advice, although his web site appears to be active. I also purchased some high quality light bulbs from him which made a very big difference on the rear lights (which I did not put on a relay set up). So at the very least, bulb upgrades do help.

Now that I have recently purchased a Series 1 E-type, I intend to do this same upgrade. The only thing that might keep me from doing it would be if I cannot hide the wiring or do it and make it at least look original to the casual observer.

I would love to see pictures of what others have done in terms of wire routing, placement of relays, etc. so I can steal your ideas.

Great thread, by the way.

Alberto

Edit: Woops!! I didn't realize this is my first post. I've been lurking quite a bit since I purchased my new to me 67 XKE (Series 1 4.2) a few weeks ago. I guess I didn't have anything constructive to add until now.

[Heuer]

No problem. The LED boards will be way under a Watt, I assume.The worry will be when the law is re-drafted in terms of lumens over ambient and all Plod traffic cars are equipped with light meters. I make that approximately the twelfth of never.

Yes but explaining all that each time you are stopped is going to be tiresome - I am sure you can refer them to this thread and all will be forgiven - Not! As regards wattage the bulbs Geoff installed have the following specifications:

"This bulb has 60 SMD LEDs to give a Super Bright light and provide a 360 degree spread of light. This bulb is designed as a direct replacement for your standard 382 filament bulb (commonly used in stop, tail, reverse and indicator fittings) to give a much brighter light. Available in red, amber or white.

Current - Wattage - Lumens
Amber - 300MA; 4.35W; 160LM
White - 270MA; 3.9W; 290LM
Red - 300MA; 4.35W; 130LM"

If those small bulbs put out this much light those LED boards are going to be too bright.

I would love to see pictures of what others have done in terms of wire routing, placement of relays, etc. so I can steal your ideas.

Info here: viewtopic.php?t=4919

[PeterCrespin]

"Yes but explaining all that each time you are stopped is going to be tiresome."

Well at least we've come full circle from 'Can't see 'em, no point' to 'So bright they're bad'. :-)

Everyone has their own risk tolerance, but from memory Plod weren't even stopping the blatantly illegal 'Look at me, I've got front fog lights as well as headlights' idiots, whose numbers had proliferated hugely before I left. Call me a risk-taking loony, but I put worrying about tiresomely frequent stops of a well-driven E-type for LEDs, at about the thirteenth of never.

Dunno, I'm possibly the mouthy outlier here, because I don't care for Miata seat protection, LED police stops or cruising at 4000 rpm all day with an original air filter and dim instrument lights. Different strokes. <Shrug>

[Dave K]

Lets be honest here the amount of cars I see driving around with one headlight on or one headlight blinding the on-coming traffic and the other normal or driving with brighter headlights than is legal or blue headlights, one tail light light out etc, etc I thiink the odds of being stopped on the rare times I drive the car at night will be very slim.

I also live in Worcestershire where there are about 2 police cars in the whole county, I saw one of them last week :D

Dave