Technical Reversing Light is Pants....
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Technical Reversing Light is Pants....
TrevC
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I just found this video, which explains potential problems with using leds in place of filament lamps:
[ame]https://youtu.be/tkPGqM0Sl64[/ame]
The items in the video are much smaller than the P21W equivalent that I've used, so can't dissipate heat so well. I will, however, conduct some tests with the other Halfords lamp in the pack. I haven't got Big Clives thermal imager, and I don't want to trash the lamp, but I have a multimeter and I/R remote thermometer, so I'll report my findings when I've had a chance to play. Of course, in a reversing lamp application, there's not much time for the heat to build up anyway.
[ame]https://youtu.be/tkPGqM0Sl64[/ame]
The items in the video are much smaller than the P21W equivalent that I've used, so can't dissipate heat so well. I will, however, conduct some tests with the other Halfords lamp in the pack. I haven't got Big Clives thermal imager, and I don't want to trash the lamp, but I have a multimeter and I/R remote thermometer, so I'll report my findings when I've had a chance to play. Of course, in a reversing lamp application, there's not much time for the heat to build up anyway.
Interesting article/information and for those small T10 bulbs (with load resistor) I would say (as a retired electronics engineer) basically factually accurate.
Some points to note.
1) Total heat dissipation of the LED bulb (with loading correction) vs normal bulbs will be nominally the same.
2) Bulbs dissipate their heat via the glass envelope (large surface area) and conduction through to the base connections. This means that hot spots are minimised
3) In the case of the T10 bulbs (with loading resistor) the wasted power has to be dissipated in and over a very small surfaced area component (the resistor) by radiation and thus the bulk of the heat will be conducted away via the circuit board tracks to the connection terminals.
4) With (3) in mind the P21W LEDs are a completely setup. First of all they have the traditional large bulb metal base through which loose heat through thus reducing hot contact spots. Secondly the Halfords ones in question have an upper body metal casing parts (ribbed = increased surface area) thus improving matters.
5) I'm not personally concerned about issues with the Halfords P21W LED bulbs especially when used in a reversing lamp.
Some points to note.
1) Total heat dissipation of the LED bulb (with loading correction) vs normal bulbs will be nominally the same.
2) Bulbs dissipate their heat via the glass envelope (large surface area) and conduction through to the base connections. This means that hot spots are minimised
3) In the case of the T10 bulbs (with loading resistor) the wasted power has to be dissipated in and over a very small surfaced area component (the resistor) by radiation and thus the bulk of the heat will be conducted away via the circuit board tracks to the connection terminals.
4) With (3) in mind the P21W LEDs are a completely setup. First of all they have the traditional large bulb metal base through which loose heat through thus reducing hot contact spots. Secondly the Halfords ones in question have an upper body metal casing parts (ribbed = increased surface area) thus improving matters.
5) I'm not personally concerned about issues with the Halfords P21W LED bulbs especially when used in a reversing lamp.
TrevC
Established member
Agree with all your points S130. I've now performed some simple measurements on the Halfords led. I used my multimeter to measure the resistance across the terminals, and it read open circuit on all ranges, which suggests there is no load resistor across the input. I then measured the current at 12V, which was 0.36A, giving a power dissipation of 4.32W. The filament lamp came out at 21W, amazingly!
So, the led array has to get rid of, probably, about 5W under engine running conditions. Unfortunately I couldn't find my thermometer, but the metal case didn't get too warm after a couple of minutes, and as you said it is mildly finned. There appear to be 21 leds. If we assume they are arranged in groups of 3 in series, like the ones in the video, that would be 7 strings of leds each taking just over 50mA. This seems about right. Presumably a few hundred mA is enough that the bulb failure circuit doesn't trip, without the need for a resistor.
I wasn't prepared to take my lamp apart, but this seems to be a properly engineered unit. It's a shame that none of these lamps are type approved as in a P21W application they would be fine, provided they met the luminance requirement. I too am a retired engineer, please feel free to criticise the above!
Finally, you may well enjoy trawling Big Clives YouTube channel. I found his videos informative, amusing, and sometimes scary when you see what's available on line!
So, the led array has to get rid of, probably, about 5W under engine running conditions. Unfortunately I couldn't find my thermometer, but the metal case didn't get too warm after a couple of minutes, and as you said it is mildly finned. There appear to be 21 leds. If we assume they are arranged in groups of 3 in series, like the ones in the video, that would be 7 strings of leds each taking just over 50mA. This seems about right. Presumably a few hundred mA is enough that the bulb failure circuit doesn't trip, without the need for a resistor.
I wasn't prepared to take my lamp apart, but this seems to be a properly engineered unit. It's a shame that none of these lamps are type approved as in a P21W application they would be fine, provided they met the luminance requirement. I too am a retired engineer, please feel free to criticise the above!
Finally, you may well enjoy trawling Big Clives YouTube channel. I found his videos informative, amusing, and sometimes scary when you see what's available on line!
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I swapped out all the rear bulb's on the Stilo for Bosch's Pure Light bulbs and the difference is huge. A good cheap mod and everything is about twice as much light. If you have a Halfords trade card it's about £20 ish for the full set.
In the UK at least, the reversing light is the one external light that does not have to be an approved type so fitting an LED replacement bulb is not a problem. Subject to the "must not dazzle or distract other road users" and it only coming on with reverse selected you could fit a 55W driving light if you wanted to.
Robert G8RPI.
