How bright is an 18 watt 12v dc light?

[misterW]

Bright enough to read by? For example, this one:

http://www.rvpartscenter.com/ProductDet ... 48&CID=213

I'm looking for one or two lights to put above the bed. 18 watts sounds low, but I'm only familiar with bulb wattages on AC circuits.

Thanks in advance!

[zipz71]

18 watt should be plenty bright. To give you some idea here are some automotive bulbs for comparison
957 bulb (dome lamp) is 10 watt
921 bulb (hi mount brake light) 18 watt
1156 bulb (backup light) 27 watt

[teardrop_focus]

Good thread! May I steer it slightly off course?

I had been thinking of going old-school incandescent for our teardrop interior lighting. Say, two 1156s providing indirect light... (one in each front corner) (yes, I know leds are far more efficient)

What's the amp draw for an 1156's 27W @ 12V? I don't know the formula...

Thanks!

[bobhenry]

Way too much info ???????

http://www.gelighting.com/na/business_lighting/education_resources/literature_library/catalogs/downloads/auto_08_index_specs.pdf

1156 & 1157 I used as porch lights they light up 30 - 40
feet like daylight

Inside I used the small clearance bulbs. ( sorry forgot the #)
They provide more than enough light to move about and
even find things in the back of the cabinets.

here is a chart of the more popular ones

[jss06]

Good thread! May I steer it slightly off course?

I had been thinking of going old-school incandescent for our teardrop interior lighting. Say, two 1156s providing indirect light... (one in each front corner) (yes, I know leds are far more efficient)

What's the amp draw for an 1156's 27W @ 12V? I don't know the formula...

Thanks!

Power (watt or P) = Voltage (volts or V) x current (amps or I).

So I=P/V

In this case I=27w/12V=2.25 Amps

[bobhenry]

So an 1157 taillight filiment draws .59 amps and
generates 3 mean spherical candle power or a 7
watt bulb ( about the same as a large clear
christmas light )

Step on the brake and you get 2.1 amp draw
generating 32 mscp or a 25 watt bulb

1156 is the same as 1157 with both filiments lit

the 921 bulb is 1.4 amp draw generating 21 mscp
at 16.8 watts

so the 921 is a close match to your 18 watt target
These bulbs are small and easily incorporated in an
unusual fixture or even incorporated with your AC fixture.

I toyed with seperate switching of an 1157. By doing
this you can have a low by using the tail light only
7 watts and click another switch to energize the brake
light also and have 25 watts of light.
ie "mood lighting"



My 1157 amber porch light

[Dale M.]

IT all depends where you mount it.... If its on bulkhead behind you so light is coming over your shoulder while reading in bed its will probably be ok....

I would think something ones below center mounted on wall would be really cool....

http://www.vintagetrailersupply.com/Dou ... ts-453.htm

OR something like these converted to LEDS...



Dale

[bobhenry]

Here is my 7 watt christmas bulbs in action. In the pic it is just getting dusk.

I know I am a bit off topic since these are actually
AC but it shows what 14 watts (2 lamps) do to illuminate
the interior, but after all watts is watts !
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here is a couple of the little lamps.

[teardrop_focus]

Bob, thanks for clearing up the differences between an 1156 and 1157... from my years as a gas jockey and the older Fords I've owned, I was all over the 1157 and actually had thought of switching between the two filaments.

I only thought, erroneously, that an 1156 single-filament somehow wouldn't be as bright as an 1157 at full throttle. Looks like I'll try to do the Hi/Low-switched 1157.

Again, I know LEDs are much more efficient or have an extremely low amp draw, but, dang it, I don't particularly care for the strange, "cold" light they put out when in bed, reading a book. There are other places I can use LEDs, though.

Dale, thanks for the link.

misterW, thanks again for starting this thread...

John/jss06, thank you very much for posting the "paper amps" formula.


to you all.

[Cliffmeister2000]

Keep in mind, those incandescent bulbs get hot. I have cracked the plastic case on the dome light in my galley because I left it on too long (I was trying to see how long it would take to drain the battery using just the lamp).

[bobhenry]

That is exactly why I went to the little clearance bulbs ( 912 I think)

The wattage is so small that there is not much heat
generated and the battery drain is much smaller.
Better to be able to see a little than to cuss the dark
when you have drained the battery.

The 1157 porch light is only on a short while
(maybe a trip to the car for something) but the
galley light can be on for an hour or more that
is why they are small

[and there are 2 just in case one dies an untimely death.]