L.E.D Bulbs, deabte . . .

[(RIP) PLANK]

I am considering upgrading the interior lights in my caravan to L.E.D bulbs for power saving. But do they really save any power?

The caravan is 12v (obviously) and LEDs run at 3-5v (I think) so need some kind of ballast resistor to allow for this (I think?)

So whole the LED itself may only draw milli amps what does the whole 12v LED replacement bulb draw? has anyone put a meter in line and tested this? O do they have LED bulbs they could test for comparison?

This sounds like a job for 96Terrano to me :thumb2

[96terrano]

why don't you just get replacement bulbs for the 12v fitting? saves messing about with ballasts and step-down transformers

[(RIP) PLANK]

why don't you just get replacement bulbs for the 12v fitting? saves messing about with ballasts and step-down transformers

you have missed the point entirely :doh

I am talking about replacement bulbs! they have a built in ballast resistor as LEDs don't run on 12v! Therefore the resistor wastes power as heat. So are the replacement bulbs really that much more efficient than the old ones?

:thumb2

[Fez_uk]

alot of the leds are wired to accept 12v or near enough. With very little or no ballast resistor.

[Paul]

A mate of ours swears by them, abit on the dear side to buy but he says he can use them all on @ night and the batt lasts alot longer before needing recharge..

[(RIP) PLANK]

alot of the leds are wired to accept 12v or near enough. With very little or no ballast resistor.

yes that is my point, an LED bulb runs at 12v but how much current does it use as compared to the filament bulb it replaces, I was hoping someone who has LD bulbs could put an ammeter in line and compare :nenau

[Fez_uk]

What i mean is some are wired in series and some parallel to get it near to 12v.

It all depends on what LEDs are used. Some pull more amps than others. All i know is they use less and usually have a clearer light.

[(RIP) PLANK]

What i mean is some are wired in series and some parallel to get it near to 12v.

It all depends on what LEDs are used. Some pull more amps than others. All i know is they use less and usually have a clearer light.

What we all assume is that they use less! and to be fair the LED's would, but does the completed bulb use less? I was hoping for a tried and tested answer rather than the hype, I suppose I will have to buy some and try it (with a meter) myself :thumb2

[Lazy-Ferret]

Basically, the resistor is used to limit the current to the LED, which is in series with the LED, so apart from a bit of wastage in heat, there is very little lost by the resistor.


Think of it as a hose pipe running out of a water butt, if you put a kink (Resistance) in the hose, it slows the water down, so it takes longer to flow away, but ultimately there is no loss of actual water.

[(RIP) PLANK]

Basically, the resistor is used to limit the current to the LED, which is in series with the LED, so apart from a bit of wastage in heat, there is very little lost by the resistor.


Think of it as a hose pipe running out of a water butt, if you put a kink (Resistance) in the hose, it slows the water down, so it takes longer to flow away, but ultimately there is no loss of actual water.

the water analogy is interesting but the kink will have several effects! the most interesting one being and increase in water pressure!

The LED bulb question is a real one, example: take the bulb out of your indicator in the front (most cars) and the remaining bulb will flash twice as fast as the relay needs the resistance in m=bot to be equal to function correctly. SO now put in LED's wired in series/ parallel or both to make them run on 12v, the relay will still operate much to fast at the resistance is so low - the answer, put a ballast resister in the bulb, the equation is I=V/R (ohms law) so now the LED bulb is using the same current as the filament bulb!

In modern cars that use LED's as standard they have a lower voltage circuit for this so the current consumed is less!

So you see my point, LED's use less power YES! But do LED bulbs? Unless you compare with an ammeter you will never really know :nenau

example: http://www.ebay.co.uk/itm/2x-501-W5W-T10-HIGH-POWER-CREE-XENON-PURE-WHITE-SIDELIGHT-WEDGE-LED-BULBS-/310407328240?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4845b7f1f0

Read it carefully, it claims the CREE LED is 1.5 watts, not that the bulb is 1.5 watt, it would be worth putting a meter in line!

[Lazy-Ferret]

the water analogy is interesting but the kink will have several effects! the most interesting one being and increase in water pressure!

The LED bulb question is a real one, example: take the bulb out of your indicator in the front (most cars) and the remaining bulb will flash twice as fast as the relay needs the resistance in m=bot to be equal to function correctly. SO now put in LED's wired in series/ parallel or both to make them run on 12v, the relay will still operate much to fast at the resistance is so low - the answer, put a ballast resister in the bulb, the equation is I=V/R (ohms law) so now the LED bulb is using the same current as the filament bulb!

In modern cars that use LED's as standard they have a lower voltage circuit for this so the current consumed is less!

So you see my point, LED's use less power YES! But do LED bulbs? Unless you compare with an ammeter you will never really know :nenau

example: http://www.ebay.co.uk/itm/2x-501-W5W-T10-HIGH-POWER-CREE-XENON-PURE-WHITE-SIDELIGHT-WEDGE-LED-BULBS-/310407328240?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4845b7f1f0

Read it carefully, it claims the CREE LED is 1.5 watts, not that the bulb is 1.5 watt, it would be worth putting a meter in line!

Unfortunately, the Water analogy only works to a point:bow

We are off out, but I do have a few 12v LED bulbs here, so I will try and measure it later for you.

The main problem is, as you say, Indicators, and some CanBus systems require the bulb to draw a certain current, in order for them to be able to monitor the bulb is working, and if you look, you will see many LED lamps that say they contain a ballast resistor in order to fool the cars ECU into thinking it is a normal bulb. This Ballast resistor is fitted in parallel to the LED and it's resistor though, so the majority of the current then passes through that, and is totally wasted in heat.

Those would obviously not be the sort you put in a Caravan, as it would be pointless.

[arcascomp]

I have some 12v LED's that claim to be as bright as a 20W halogen and I'm fairly sure they are, perhaps a little less spread out, but the cree bulb used is 3W and the whole sheebang is rated at 4W so a little loss. but still way less than the halogen it replaces.

[(RIP) PLANK]

I have some 12v LED's that claim to be as bright as a 20W halogen and I'm fairly sure they are, perhaps a little less spread out, but the cree bulb used is 3W and the whole sheebang is rated at 4W so a little loss. but still way less than the halogen it replaces.

but the point is still misses, while the LED may be lower wattage is the lED plus resistors etc, that make up the 'bulb' actually lower wattage?

I = V/R: So if the supply V is 12 and the v needed by the LED is 4 and increasing R is used as a method of to make up the value of V then I would be the same :nenau

So has anyone actually put any of these claims to the test with an ammeter?


Example: http://www.ebay.co.uk/itm/2x-5-SMD-LED-AMBER-ORANGE-INDICATOR-SIGNAL-TURNING-SIDE-LIGHT-BULB-T10-W5W-501-/300635570487?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item45ff46c137

These bulbs can't possibly use less power or they simply wouldn't work!

[arcascomp]

Nope but LED is 3W at 12V, Bulb is packaged and rated as 4W at 12V, light out is close to Halogen 20W at 12V.

So, the LED saves 17W but after losses in the bulb package it only saves 16W.

Have I tested, nope, but my bike lights run substantially longer on LED than Halogen with the same battery pack.

[briggie]

another equation you might be interested in for this debate ...

p= i x v

p ( power measured in watts ) can be dissipated as heat

i= current measured in amps

v= voltage measured in volts

[briggie]

you have pm plank :augie:lol

[rustic]

On my boat I converted the navigation lights to LED, they were originally 10 watts each, so less than an amp.

When I fitted LED's the power consumption dropped to 10 % of the original power..

I will find a note later and post it on the effect of putting 2 led's in series.

One string of LED's in series will take approx 20 mA 0.02 Amps.
Most LED bulbs are wired in series parallel so often have say 8 strings of 2 LED's

So current will be 8x 20 mA or 160 mA or 0.16 amps.

If that helps for now.

[(RIP) PLANK]

so, in transposing that equation if V = 12 and I = 10 then P = 120

so if a light is giving off 120 watts at 12 volts it must be drawing 10 amps regardless of it's filament or LED status.

In this case the 'missing' power is used by the resistors that are allowing the LED's to run at 12 volts. :nenau

even if one considers that LEDs of much lower wattage are used to produce the same quality of light (lumens/kelvins?) then by default some power must be being wasted by running LED's at 12v :nenau

I have ordered 10 Led "bulbs" and will do some measuring when they arrive, though they are on a slow boat from China so I won't hold my breath :augie

[briggie]

the pm i sent you explains it plank , if you dont fall asleep reading it :lol

[briggie]

i love a good debate , im often called a great mass debator ...... or i think thats what they said :o

[(RIP) PLANK]

I have had a skim through it, but the mainstay of the power consumption charts seem to be relating to LED's at their optimum operating voltage, the power loss from and additional components needed to convert another voltage , 12v for example, to the ideal LED operating voltage still seems to be another issue and must use more power!

Another interesting thin I have found by reading the listings of ebay LED vehicle bulbs, very few make any mention of the power consumption or give any figures, it just seems 'assumed' that consumption will be lower. As it would be if you replaced a 4v filament bulb for a 4v LED, In a vehicle application this makes little difference and there are other benefits to LEDs but if lowering power consumption is your aim then maybe LED bulbs aren't all they are assumed to be :nenau

[Moochin]

18 years ago I completed a National Diploma in Electronics, I have just read through this and decided I haven't the first clue how I managed to pass.

[96terrano]

18 years ago I completed a National Diploma in Electronics, I have just read through this and decided I haven't the first clue how I managed to pass.

:lol

[(RIP) PLANK]

you would love the stuff me an Briggie have been going through then! A nice university research paper on LED's with load of equations. We are both ex tv engineers, from when they were big and heavy and made of glass and videos had tapes that top loaded :thumb2

[briggie]

memories plank ?

http://sxemi.net/tvs%20Philips2.htm

:augie:lol:lol

[briggie]

oh the fun of shorting the final athode to the chassis ..... those where the days :lol:lol:lol

[(RIP) PLANK]

I gave myself a shock doing that once! my hair stood on end and my tie straight out at 90% in front of me! And i burnt two small holes in my finger right down to the bone :eek:

[solarman216]

when I was a kid, my dad was always bringing old TV sets home to try and repair, needless to say most got bunged in my direction to pull to bits, I found the quickest way to kill earth worms was the spark from the final anode, what fun we had then, could you see that today, Rick

[(RIP) PLANK]

I don't think plasma screens are quite as lethal :augie

[(RIP) PLANK]

Rustic - for some reason the quote button isn't working but cheers for that! As i really need to drop my power consumption now the nights are drawing in :thumb2

[edgerton19]

To answer the original question it depends on the type of lighting fitted in your caravan. If you have fluorescent lights fitted the LEDs will be only very marginally more efficient as their efficacies are similar (but the latest LEDs win).
If you drive them via a resistor to control the current you are on a looser as the resistor just converts the excess voltage (and hence power) to heat. If you buy switch mode LED drivers the conversion efficiency should be over 90% and you can series LEDs, work on each LED needing around 3 to 3.3V at their rated current.
The big problem with home construction is getting the heat out of the LED body, at work we build high power LED light engines on PCBs with an aluminium substrate and these are then mounted on aluminium heatsinks. Small low power LEDs can be mounted on FR4 but you still need to back the assembly with some form of heatsink.
In your position I would look at a ready made solution, Labcraft got a good write up in RadCom for their 12V LED lamps and no I don't work for Labcraft but I do work for a UK company that manufacture 100,000 LED drivers and light engines a month!!

[kitchenman]

http://www.ebay.co.uk/itm/10x-42mm-Car-Auto-Interior-Festoon-Dome-16-SMD-LED-Light-White-Reading-Lamp-Bulb-/320989806972?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4abc7bc17c

Have a look here,

[(RIP) PLANK]

To answer the original question it depends on the type of lighting fitted in your caravan. If you have fluorescent lights fitted the LEDs will be only very marginally more efficient as their efficacies are similar (but the latest LEDs win).
If you drive them via a resistor to control the current you are on a looser as the resistor just converts the excess voltage (and hence power) to heat. If you buy switch mode LED drivers the conversion efficiency should be over 90% and you can series LEDs, work on each LED needing around 3 to 3.3V at their rated current.
The big problem with home construction is getting the heat out of the LED body, at work we build high power LED light engines on PCBs with an aluminium substrate and these are then mounted on aluminium heatsinks. Small low power LEDs can be mounted on FR4 but you still need to back the assembly with some form of heatsink.
In your position I would look at a ready made solution, Labcraft got a good write up in RadCom for their 12V LED lamps and no I don't work for Labcraft but I do work for a UK company that manufacture 100,000 LED drivers and light engines a month!!


Interesting stuff but! my intention was/is always to use something ready made i.e. the ready made Led "bulbs" available to for use in cars. My point was that these all seem to use resistors that, as you say, waste the extra power as heat. In the case of indicators they would have to do this to work! So while there are benefits to LED replacement bulbs is energy saving one of them or is it just an assumption we all make.

So if i buy these for example:

http://www.ebay.co.uk/itm/2-x-LED-Light-Bulbs-BA15S-1156-382-P21W-Indicator-Bulb-24-LED-White-/270868469102?forcev4exp=true&forceRpt=

note the seller makes no claims regarding their efficiency! They can't use less power as they must use a ballast resistor to make the flasher unit in the car work and therefore use the same power in total!

[(RIP) PLANK]

http://www.ebay.co.uk/itm/10x-42mm-Car-Auto-Interior-Festoon-Dome-16-SMD-LED-Light-White-Reading-Lamp-Bulb-/320989806972?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4abc7bc17c

Have a look here,

They do look like they would save a significant amount of power compared to filament bulbs. Unfortunately I have no interior lights that use them :nenau

[Thomas-the-Terrano2]

well i tried to convert the caravan to leds to save power on non hook up sites.

found they ran cooler than regular bulbs, though just like the hosehold types
gave much less light than regular bulbs.

in end went back to regular bulbs which also give a warmer light than led.

[(RIP) PLANK]

well i tried to convert the caravan to leds to save power on non hook up sites.

found they ran cooler than regular bulbs, though just like the hosehold types
gave much less light than regular bulbs.

in end went back to regular bulbs which also give a warmer light than led.

there are so many different LED replacements you will be surprised! with more or less LED's and even different colour tones like 'warm white', just type G4 LED into ebay as an experiment. Noe i am convinced these will use less power as they aren't car bulbs but a BA15 base usual means indicators and as such has a ballast resistor. I think I have sussed it though and have ordered some more to day to experiment.

I will let you know how it goes :thumb2

[Lazy-Ferret]

The problem is, you are looking at just one thing, and with LED's you have to look at a much broader picture..

Even if you ignore the longer life, and less degeneration, and stick to just worried about making a battery last as long as possible.

Basically, LED's do not have to draw the same current, in order to produce the same amount of usable light...

E.g.
LED's put all their light out in one direction, so waste less light.
LED's run cool, so are wasting less energy as heat.
LED's produce a far tighter spectrum of light, so are not wasting power producing invisible Ultra violet and infra-red frequencies.

Have a look here.
http://www.ledtek.com.cn/info/faq-2011070801.htm

The next problem is deciding how much light you need, as most bulbs are measured in Watts, but that is just how much electricity is used, not how much light is put out. Currently it is very hard to work out true comparisons, not only as traditional bulbs do not always publish their light output, but also because they radiate the light in nearly all directions, where as an LED concentrates the light in a beam in just one direction.

The bottom of this site gives some comparisons of power for a given light output, http://www.designrecycleinc.com/led%20comp%20chart.html and it can be seen that they say a 5w LED is the same as a 40w incandescent light both producing 450 lumens.

So a 5w LED running on 12v would be drawing 0.42amp, as opposed to a 40w incandescent bulbs running on 12volt would be drawing 3.33amp.

A CREE LED, set up to produce 460 lumens, needs 1.5amp at a voltage of 3.25volt. the corresponding resistor for that to run on 12volt, sticking to preferred values would be 6.8ohm 13watt.

Therefore the resister would be dissipating just under 13watt, and the LED would be using just under 5watt, resulting in the LED/Resistor combination using 18w, for the equivalent of a 40watt incandescent bulb.

Having said all that, if I was making a 12v LED CREE bulb of that power, I would use 2 or 3 LED's in series, and a smaller resistor, which could drop the power to 14 or 16watt.

[cncfabs]

I dont understand what this debate is about.Ive just installed 2 4.5watt work lights on my fourtrak they light the whole place up.If i had put 2 5w sidelight bulbs there it would do nothing.In my opinion the led lights are far brighter than my headlights and use a fraction of the power.

[(RIP) PLANK]

I dont understand what this debate is about.Ive just installed 2 4.5watt work lights on my fourtrak they light the whole place up.If i had put 2 5w sidelight bulbs there it would do nothing.In my opinion the led lights are far brighter than my headlights and use a fraction of the power.

how do you know they use less power have you measured it :augie

but seriusy in the application you mention I have no doubt that they do use less power. But! try using a Ba15 LED bulb intended for a car indicator and supplied as a replacment caravan spotlight bulb and you may find you are using more power due to the "canbus" compensating components.

[mir60899]

A couple of years back I bought a roll of sticky back led strip from ebay and converted all the strip lighting in the van from twin flourescent to three strips of led. I can now run all the lights in the van, that's 6 light units and the current draw isn't even the equivalent of one of the twin strips.
The light output is if anything brighter than before and when listening to the radio on long wave (shipping forecast and all that) no interference from the ballast circuit.

[zippy656]

Swift, do a retro for some of there vans.