LED dome light

Looking at replacing the normal bulb in the dome light of the car with an LED. It's a 31mm festoon type and there's enough physical space to get in either of the ones I've found, but I need to know which will give the brightest light, a 6 SMD 5630 or an 18 SMD 4014? They are both white 6000K.

Reply to
Steve
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Assuming you mean the interior cabin light. You need the LEDS all facing the same way. If they are arranged in a 360 degree configuration most of the light not directed downward will be wasted.

I would go for the 6 off LEDs which are likely to be LED arrays anyway.

I've had mixed results with LED festoon type bulbs. The one I currently have for the cabin interior light has been ultra reliable but the previous obtained bulbs from Ebay Chinese sellers proved to be very short lived in both the interior and rear number plate applications.

Reply to
alan_m

Thanks Alan. Yes, I do mean the interior cabin light and the ones I've found are indeed all LED arrays with the SMD LEDs all facing the same way, but I just want to be sure of getting the brightest version.

Reply to
Steve

look up the led numbers on google and see the lumen outputs, pick the one with the biggest output, simples.

Reply to
MrCheerful

Most sellers don't give figures. They will give wattage figure which is a bit meaningless. The specified figures for the individual LEDs cannot be used as it the light output from the LED depends on the current through it and a reputable manufacturer would balance the current with the heat generated in the festoon bulb. Heat kills LEDs.

The latest designs from reputable brands tend to have only one or a few LED (arrays) in much the same way as touches have evolved from 40/50 LEDs to a single LED array. More LEDs don't equate to more light. My current cabin light has 3 LEDs (6000k) and subjectively gives more light than the filament bulb it replaced but this may be due more to the colour change (warm white to cool white)

In my experience some of the festoon bulbs with lots of LEDs are in fact non-standard sizes in that they may have the correct dimension between contacts but because they are 1.5x the standard width they don't fit two well. Also watch out for bulbs with large heatsinks that extend beyond the traditional glass envelope, again there may be insufficient space in the existing light fitting to accommodate the bulb. Possibly size is more important for number plate lights rather than cabin lights.

Reply to
alan_m

the specs. of the actual led are widely available (which are the numbers he is quoting) the first one for example gives 50 lumens per led, times

6 is 300 lumens
Reply to
MrCheerful

But there is often a wide gap between what is possible in ideal test conditions (as per the specification sheet) and what is actually possible in a practical design.

From a reputable manufacturer the figure is 36 lumens typical for the

5630 LED but this is for a test current of 100mA and the thermal pad kept at a temperature of 25 degrees centigrade.

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This test condition is a power of 310mW so for 6 LEDS 1.86W and 216 lumens. The test condition is at 25C which requires a substantial heat sink to maintain that temperature at 1.8W. This is not achievable in something as small as a festoon bulb. A more realistic condition may be to de-rate to a maximum power of 1W taking down the output to more like 116 lumens.

For the other device

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Each LED

20 lumens at 60mA, equivalent to 0.17W

18 LEDs

360 lumens @ 3.06W

The same test temperature are used for the test case so again de-rate to

1W and the figure drops to 117 lumens

So, no difference between the two festoon bulbs.

There is no information about how the designers have de-rated the devices to make a practical product.

As a sanity check, some of the better CREE power LEDs are approx 80 to

100 lumens per watt so both figures above appear to be somewhat optimistic.
Reply to
alan_m

Well Alan, you're obviously a guy who knows his stuff. I looked at the pdf files (well, one.... alright, a couple of pages of one) and my head is spinning and I was lost after the Table of Contents.

I had no idea it was such a can of worms! All I want is a bright interior light (preferably about 6000K - 6500K CT) in a 31mm festoon package (doesn't matter about width/depth as there's plenty of room, just as long as the length doesn't exceed 31mm) and I'm just trying to avoid buying something that's a load of rubbish and then needing to buy something else.

I take it from your info above that the two bulbs I mentioned are basically the same light output so I could go for either of those, but in the real-world situation of an interior car light, is 116-117 lumens enough or is there something out there that would be better?

TIA and thanks for your input so far.

Reply to
Steve

Steve formulated on Thursday :

I forgot to say - I'm obviously no electrician and I don't understand the relationship between Watts, mA and Lumens, but I've found a chart here

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that seems to suggest that the 4014 gives 60 Lumens at 27mA, so wouldn't 18 of them give 18 x 60 = 1,080 Lumens?

Reply to
Steve

Yes it would. Lumens is how much light is output. Watts are how much power it takes to get the light. A filament bulb will waste a great deal of power as heat. Volts X mA will give you the total power used for everything light and heat. You would need to X the 27mA by 18 to get the total current used for 1,080 LM (486mA)

Reply to
Derek P

JOOI, how much do the lamps in question cost? Is it small enough that taking a punt and reporting back would be the right answer?

Reply to
Clive George

Well yes, I suppose I could. I know they're not exactly expensive but after paying £5,500 for the car then £1,400 for the LPG conversion, £350 for cambelt/water pump, £250 for two tyres, and about £250 for all the fluids to be changed, the wife is getting a bit pigged off with me. Plus, I just thought somebody may have the knowledge and could say 'yes to that', 'no to that', or maybe recommend something different altogether.

Reply to
Steve

leave the standard bulb in.

Reply to
MrCheerful

I would suggest that the graph is wrong. If you look at the figures for all the other LED types on that page the current figure (mA) is always higher than the lumen figure (light output figure). They seem to have transposed the two numbers for that LED. This transposition is confirmed by their wattage figure. 27mA would give approx 0.1 Watt while 60mA would give approx 0.2 Watts which they claim in the orange number.

That graph gives 60 lumens @ 27mA The data sheet I referenced gives 20 lumens @ 60mA

The graph may also be showing maximum rather than typical figures so I suggest that a figure of 20 lumens at 60mA is more realistic figure.

1,080 lumens is more than you get from a 10W LED floodlight that you would fit to the outside of your house! And, those LEDs are bolted directly to the substantial finned metal casing of the floodlight in order to keep them cool(ish). 1080 lumens is typically what you would get from a main beam headlight bulb. Link taken at random
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Note how much braiding used as a heatsink! As I have said before looking at the specifications for the individual LEDs is misleading because the figures are not real world - it's the advertising hype. Heat kills LEDS so once you start getting to power approaching 1W and above the designer has to consider ways of getting rid of the heat. A large heatsink is one way, reducing the current and light output is another.
Reply to
alan_m

I take it that you are aware that at that colour temperature the light will be very cold and blue. I'd prefer about 4000K - 4700K personally.

Reply to
rp

Haha, fair enough Alan, thank you.

Reply to
Steve

Yes, I'm happy with that. I've always preferred the 'whiteness' of fluorescent lamps to 'normal' lamps in the house, it's just the way my eyes work I suppose. Our car has black leather interior and black carpets, so I think I'll stay with 6000K.

Reply to
Steve

I have a three Watt led around here somwhere that I bought off ebay. Another is tri-colour with 1W each colour. Both types have very solid heatsinks on.

Reply to
Mr Spectacular

Not a recommendation of any kind but

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have a list of bulbs where they give Brightness Efficiency figures in lumens (LM) for each of their bulbs

The only gotcha may be under what operating conditions: A lumen figure with a 12V source for some bulbs is unambiguous but when they quote a lumen figure for a range of voltages of, say, 9V to 32V is that lumen figure only true for 32V or is it the same for the whole range of voltages?

-- mailto: news {at} admac {dot] myzen {dot} co {dot} uk

Reply to
alan_m

Thanks Alan. I appreciate you were not giving a specific recommendation but I decided to go for two of the 18 x SMD4014 and just give it a go. They list the output as 280 lumens as opposed to the 6 x SMD5630, which they list as 180 lumens. I've ordered one of those as well, just to see what they are like in a 'real-world' situation.

Reply to
Steve

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