LED dome light

Steve pretended :

Ok, being as no one could give a definitive answer I got a couple of each to try. Whilst my eyes can't really see much difference between the two, I have to say that I'm well pleased with the final result. You may think differently but, for my eyes and preference, the 6000K look

*very* bright in our car at night, which is exactly what I wanted. The car has a black leather interior and black carpets so the 'whiteness' of the 6000K against that is excellent. I got them from here and can highly recommend them:

formatting link

Reply to
Steve
Loading thread data ...

I hope it works well indefinitely. I was not impressed by the 4 domestic GU10 LED lamps I bought recently, one stopped in a few days and another started to literally smoulder soon after. They have gone back to the maker and a report should be made. Good job someone was in the room or it could have been very nasty. The different model replacements have been fine so far.

Reply to
MrCheerful

LEDs ain't like filament bulbs. The light output is set by the current going through the LED. The voltage is unimportant.

With a small LED, you'd normally set that current with a series resistor. The value of that resistor is calculated knowing the supply voltage. So a resistor suitable for a 12v supply would be wrong at 32v. But with the correct resistor for the supply voltage, the light output from the LED would be the same at 12v or 32v.

Reply to
Dave Plowman (News)

It is important if you don't have the string forward voltage, typically

1.8V to 3.3V x number of LEDS in series. To put 4 3.3v leds in series you need more than 13.2 volts. To ensure decent current regulation by a series resistor the LED string voltage needs to be quite a bit lower than the supply.

The "correct" resistor is different for 12v and 32v.

R = V / I = (Supply voltage - diode (string) voltage) / LED current

So 3 leds in series with 2V forward voltage and 20ma current

12V R = (12 - 3x2)/0.02 = 300 ohms

As automotive system voltages typically peak at about 15volts that is the voltage the current needs setting for. Though it may be safer to fit a voltage regulator or a better current limiter. R = (15 - 3x2)/0.02 = 450 ohms

Or for your 32V case R = (32 - 3x2)/0.02 = 1300 ohms

Reply to
Peter Hill

As you say, a single resistor would be unsuitable for a voltage range of

9V to 32V. With a 3:1 voltage difference there will be close to a 3:1 current difference and, assuming a fairly linear current to light characteristic, a 3:1 light difference. Furthermore a single resistor solution would be unsuitable for this application the current also has to flow through the resistor generating heat.

There is likely to be a switched mode supply of some kind, a PWM (Pulse Width Modulation) circuit or an active constant current source - or a combination thereof. A common mode of failure with these car LEDs is that they start flashing when some of the supporting electrics fail.

The point I was attempting to make is that when single performance figures are quoted it's usually the best performance under the most favourable operating conditions. Unless you find a complete detailed data sheet for the device you cannot assume the real world performance figures are the same.

Reply to
alan_m

The small spotlight type LED bulbs tend to get too hot in traditional fittings - too little free flow of cooling air. I've had poor performance from these types of bulbs in the past but they were purchased from Chinese Ebay sellers.

My household lighting is now 75% LED.

I've had a lot better and reliable experience with other household LED bulbs of a larger size fitted in positions where air cooling is a lot more efficient. IMO, when buying LEDs for household use consider also buying a suitable fitting. I have a 300mmx300 cool white LED panel in my bathroom that gives exceptional illumination. In two other locations I've fitted round panel lights (cool white, 24W) of the type.

Ebay seller selected at random.

Reply to
alan_m

I have one here. It gives out an awful coloured light

Reply to
Graham T

Some people are conditioned into accepting awful white light towards the red end of the spectrum is normal :)

It's all down to personal preference and perhaps what you get used to. I personally prefer 'white' LED lighting at the blue end of the spectrum especially in a working environment.

Reply to
alan_m

The bulbs that died are in the open air almost entirely, so it was not an overheat issue caused by the fitting. I have about 75 percent led bulbs in the house (rest are halogen or cfl) and these are the first leds that have failed.

Reply to
MrCheerful

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.