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snafu7

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Howdy- I am a newby to your forum but in hope someone can set me straight on this nagging question in my mind.

I am converting my boat's 12 volt lighting to led's. In searching for replacement bulbs I have seen some led medium base, edison bulbs listed as 12 to 24volts - 9W
If a multi voltage bulb as this is used at 12v does it put out fewer lumens than if it was run at 24v ? The lamp is described as being and equal to a 75w incandescent- so will it be at 12V ? or just at 24v?

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Snafu
 
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derek

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Wattage is the power output, it depends on the voltage and the current. If the voltage is 12v then the current would have to be a certain amount of amperes to get to 9W ; if the voltage was doubled then the current would be halved to have the same power output of 9W.
 

snafu7

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Hmm - first to admit I'm not great with this stuff.
24v x .375A = 9w
12v x .75A= 9w
so are you saying that as long as the 12v system can deliver .75a to the lamp it will produce the same lumen as the 24v system at .375A

I had never thought about this until I was reading reviews on Ebay/Amazon and a couple people stated
that there was a large difference in lumen output between 12-24v and suggested buying a bulb classified as 12v only and not one marked 12-24V bulb.
THX
 

derek

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Sorry I should correct myself, Watts should be power consumption, lumens should be light output; some light sources produce more lumens per watt consumed, eg. led lamps compared to incandescent lamps.
 

derek

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Lumens per watt could be seen as a measure of efficiency as most led lamps don't produce as much heat energy as an incandescent lamp.
Even then it is not that simple as you'd also need to factor in equipment (lamp holder cost and maintenance per square meter) for the area that needs to be illuminated.
 

snafu7

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Do you think the sellers description as being a equivalent to a 75W incandescent is based at 24v and hence
the reviews were accurate.
 

snafu7

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Thx for your help Derek- Most LED bulbs mention what the bulb equals to in an incandescent-- but give no specs. They just casually say these bulbs are equal to (no mention of voltage) a 75w bulb. I believe the 9w would be closer to a 60W- anyway the question is

If you had a bulb listed as 12v - 24V would the bulb ran at 24V be brighter ?
 

littlespark

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With old filement lamps, then yes, half the voltage would give off half the brightness, but with LED, I believe the the brightness is constant whatever voltage. The electronics inside the lamp can deal with it.

Some mains powered lamps can be rated at 100v - 250v so the same lamp can be manufactured for different countries.

The light output should be the same.
 
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There are special bulbs for cars and boats with built in pulse width modulated current regulation and they can be supplied 10 - 30 volt and output stays the same this firm Bedazzled Protected LED Lights 10-30v ideal for 12V 24v environments - https://bedazzledledlighting.co.uk/ seem to specialise in them.

However most household 12 volt bulbs use three LED's and a resistor, LED is around 3 volt, but are current dependent so need some thing to stop them using too much, so a simple resistor is used with 12 volt and a capacitor with 230 volt AC. There is nothing to stop using a capacitor with 12 volt AC as long as the Hz is know i.e. 50 Hz, but many volt droppers used switch mode technology and are in kHz range so in the main simple resistor.
 

Lucien Nunes

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To summarise the above:
  • An LED product rated for 12-24V DC will have internal driver electronics to regulate the current so that the power & brightness is sensibly constant over that voltage range.
  • An LED product rated for 12V DC only, will normally have passive current limiting and would overhat and fail rapidly at 24V. The current is set by the difference between the LED string forward voltage (typically 9V) and the supply, which on 24V will be 15V instead of 3V resulting in a 5-fold increase in current.
  • An LED product rated for 24V DC only will barely light at all at 12V, because the normal forward voltage of the string of LED chips will be higher than 12V and hardly any current will flow.
 
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I agree with what you have said, so an LED designed for 12 volt so 3 LED's and a resistor, if supplied with over 12 volt the LED voltage will still be 9 volt approx until it burns out, so instead of 3 volt across the resistor at 12 volt, if the stage charger is charging at 14.8 volt then you have 5.8 volt across the resistor so nearly twice the design current.

So as you say, to summarise a LED package designed to be powered from a 12 volt regulated supply is not suitable for use on anything which uses a lead acid battery which could be on charge.

I did consider cheap domestic LED packages for the caravan, and with a forward bias of 0.6 volt on a diode fitting 4 diodes could drop the volts, but then once off charge the LED's may not light, using a resistor one would need to either use trial and error or calculate size, but again LED's would be dim when not on charge, plus heat, so it would need a DC to DC inverter, at 24 volt actually not so bad a 7812 voltage regulator could drop voltage, together with a resistor so you could use 12 volt bulbs with 24 volt easier, but a 7812 will drop the voltage around 1 volt so again when not on charge the lamps would be under voltage.

Plus still looking at the heat, pulse width modulated or switch mode control is far better, less heat produced and the DC to DC converters will cost more than the bulbs with the SMP or PWM power regulator built in, so not worth doing, may as well get the right bulbs for the job.
 

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