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Re: Dim Panel Lights

Subject: Re: Dim Panel Lights
From: DANMAS <>
Date: Thu, 30 Apr 1998 19:49:34 EDT
In a message dated 4/30/98 1:53:07 PM Eastern Daylight Time, writes:

> Lamps labeled 1449 are 14v   /   2.8w   /  .20a
>  Lamps labeled 1446 are 12v   /   2.4w   /  .20a
>  (You'll have to ask the "Master" to see if that works with ohms law)


Till the "Master" gets here, will you settle for the opinions of Masters, Dan
Masters, that is!

First of all, a reminder.  You don't have 12 volts in your car if your
electrical system is up to snuff -- you have *around* 14 volts as long as the
engine is above idle speed (just so we are comparing apples to apples, let's
assume exactly 14 volts).  That means all devices -- lights, wipers, horn, etc
-- are fed 14 volts.

At 14 volts, the 1446 bulb will draw 0.23 amps, and dissipate 3.2 watts.  A
bulb rated at 2.2 watts at 12 volts will draw 0.18 amps when supplied with 12
volts.  When supplied with 14 volts, the same bulb will draw 0.21 amps, and
dissipate 2.9 watts.

I don't have his original post, but if I remember correctly, Jack said a #52
bulb was rated 2.2 watts at 12 volts, while a #53 bulb is rated at 2.2 watts
at 14 volts.  If that is correct, I offer the following summary:

At the normal automobile voltage of 14 volts --

#52       0.21 amps     2.9 watts
#53       0.16 amps     2.2   watts
1146     0.23 amps     3.2 watts
1149     0.20 amps     2.8 watts

Thus, a #1146 bulb will generate 45% more heat and light than a #53, 10% more
than a #52, and 14% more than a #1149.  The additional light is very welcome,
but I'm not so sure about the heat.  The bulb housing in the gauges is quite
small, so heat can be a problem.  Evidently, though, if they have worked all
these years with a #52 bulb, then I don't think the extra 10% will cause a

You may want to check my math (my math is OK, but sometimes I get confused and
use the wrong data in the equations). Also, a couple of other things to keep
in mind. 1) these numbers are approximate,  2) A 20% increase in voltage does
not cause a 20% increase in current in a light bulb.  As the temperature of
the element goes up, the resistance also goes up.  Using the data supplied,
the resistance of a #1146 bulb at 12 volts is 60 ohms.  I used 60 ohms in the
calculations above, but the actual resistance at 14 volts will be more, so the
wattage and current will be less than shown in the calculations.  How much
difference, I don't know.  That data is just not readily available.

Dan Masters,
Alcoa, TN

'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74

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