Source for LEDs for those of you wanting to play

[Anthony]

Hi,

Just found this website that seems to offer just about every LED imaginable:

http://shop.dotlight.de/shop/index.php

inc 3 watt white ones. After all the talk over using LEDs for nav and interior lights I thoughts some of you maybe interested.

If you do experiment please lets us know how you get on.

Ants

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[snowleopard]

looks interesting. anyone know how many 1w or 3w leds you need to equate to 10/25w filament bulbs?

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[aitchw]

It's a slightly difficult comparison as the light is of a different character, like comparing energy saving domestic bulbs with tungsten equivalents. I don't know the lumen values but I would say no more than two 3w leds and possibly nearer to four 1w. There is probably an advantage in using small arrays of multiple leds in terms of spread. They are easier to tailor to an application. All very intuitive though, on my part.

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[bedouin]

Re: Source for LEDs for those of you wanting to pl

I've just bought a commercial LED based nav light (combined Tricolour and Anchor) that uses one LED for each sector to provide 2NM visibility (i.e. equivalent of a 25W tricolour).

That draws 0.48A, i.e. takes about 6W. Therefore I would guess that each LED is approximately 1W



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[G8KMH]

Re: Source for LEDs for those of you wanting to pl

Closer to home, RS Components also have them for roughly comparable pricing, including 5W units. And, of course, there is ebay... Search either site for Luxeon

A 1W unit draws about 0.35A from the data sheet. According some information I've seen, a 1W LED is roughly comparable to a 5W tungsten bulb. But, and a big but, LED's have output in particular directions so it is comparing apples and oranges.

Lehane


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[wooslehunter]

Re: Source for LEDs for those of you wanting to pl

Not necessarily so - it depends on how the LEDS are driven.

An LED is current driven. In general terms, the simplest way is to use a series resistor, the bigger the better within reason. Since the LEDs' forward voltage drop can vary quite a bit, a large resistor irons this out effectively becomming a constant current source. The problem is though that big resistors will dissipate lots of energy and you'd need a high voltage to drive them. If the voltage is fixed at 12v, you have only one practical choice. Two 1W LEDs in series drop around 7-8v together. Hence, you'd have to drop the rest of the battery voltage across a resistor. 1W LEDs are generally driven at around 350mA. Hence it's possible that your 6W solution doesn't actually drive the 1W LEDs at 1W each. Some of the power could be dissipated in resistors. It's possible since these 1W LEDS get VERY hot and need heatsinking. It would be easiest to de-rate the LEDs and lose some power in resistors.

The other way is to use a more complex solution that can get a far higher efficiency and drive the LEDs with the constant current they require. This is by far the best solution technically in terms of efficiency but it is more complex and therefore more expensive. If this is what's inside your nav lights then the heatsinking issues will also have been solved adding to the cost.

The company I work for make LEDs by the way - not the 1W/3W types though but the principles are the same.

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[bedouin]

Re: Source for LEDs for those of you wanting to pl

I don't think a resistive solution would be adequate for navigation purposes. The colour balance of a white LED is dependent on the current so you need to maintain a fairly accurate current to make sure your white light is white.

I can't see the details inside the unit I have, but it does use an LM317. As I said it draws 480mA and claims to operate down to 8V. From those figures I can't decide how it is configured; but clearly it can draw as little as 4W at the minimum supply voltage - hence my guess that the LEDs are each 1W.

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[NigeCh]

It\'s odd to go for a variable supply

when say an L78xx series regulator working from a variable 10 to 15v supply could provide a just less than max forward voltage and a constant current if linked into a switchable 7555/irf520 circuit to drive a) the tricolour and b) the all-round-white.

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[William_H]

Re: Source for LEDs for those of you wanting to pl

+Hello Bedoin the LM317 regulator operates with 1.2 volts between the adj terminal and the output terminal. it operates brilliantly as a constant current source by puting a 10 ohm resistor between output and load and the adj terminal connected to the load. The 10 ohm resistor drops 1.2 volts at 120ma and the regulator increases in through resistance if current rises to maintain the 1.2 volts. (1 ohm resistor gives 1.2 amp) So if a LM 317 is used and if you want the LEDs to function at 10 volts input then the LM 317 would have to drop 1.2 volts plus .7 min for the pass transistor leaving 7.5 volts for LEDs. In this example of 120ma in at 10 volts you use 1.2 watt of which .9 watt is used in LEDs. At 15 volts input you would use 1.8 watts again with .9 watt used in the LEDs. There probably are other circuits which give less volt drop across the current regulator but ultimately you will be stuck with .7 volt drop at 10 volts (a silicon transistor) rising to 5.7 volt drop at 15 volts input. All this from theory of course but ultimately your leds will be less efficient (though just as bright) at normal voltages if they are to operate at at lower voltage.
I have done some fiddling with individula hi intensity LEDs dropping 2 to 2.6 volts at 20 ma they are quite bright for in my case shining on the jib for night sailing but they are so focussed that they would have to be ganged pointing in different directions for Nav lights but they are cheap at around 80 pence each. In this case 4 in series would not work until battery was over 12 volts so you would be stuck with only 3 in series if you used the LM317 as a current regulator. In practice it is easier to use 3 in series with a 325 ohms to give full output at 14 volts and less at 12 volts.
Regards will

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