24v bulb in a 12v system

Skipper

Skipper

.
Oct 9, 2008
1,742
Bristol 29.9 Dana Point
I have a 10w 24v bulb in inventory. Long story. If I install it in the 12v system, it will use 5watts, .417 amps. And will be about the brightness of a 5 watt bulb. Right?
 
sunman

sunman

.
Jul 29, 2009
112
Mac Mac 26D Suwannee
U have it in ur inventory right?
so why dont U try it, and let us know, U got the bulb:doh:
 
C

Chief RA

.
Nov 26, 2012
2,315
Catalina 250 Bodega Bay CA
ALNims will be correct. Realize that you are dealing with an impedance not fixed resistive # of ohms. The filament exhibits less glow at lower current and voltage and it is not linear. Lower temperature means higher impedance with less thermal activity. Chief
 
jlp0217

jlp0217

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Jun 27, 2014
117
Jeanneau Moorings International 50 Everett
Everything else equal voltage and current will be 1/2. Power will be 1/4 (2.5 W). But since it won't reach normal operating temp, I'd expect greater current, less lumens.
 
Skipper

Skipper

.
Oct 9, 2008
1,742
Bristol 29.9 Dana Point
sunman said:
U have it in ur inventory right?
so why dont U try it, and let us know, U got the bulb:doh:
Click to expand
Let you know what? The answers to my questions? It's math, using expertise relating to the topic, which I was seeking. Others understood, and answered effectively.
 
Skipper

Skipper

.
Oct 9, 2008
1,742
Bristol 29.9 Dana Point
Chief RA said:
ALNims will be correct. Realize that you are dealing with an impedance not fixed resistive # of ohms. The filament exhibits less glow at lower current and voltage and it is not linear. Lower temperature means higher impedance with less thermal activity. Chief
Click to expand
Got it. Thanks, Chief.
 
Ken Cross

Ken Cross

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Oct 24, 2010
2,405
Hunter 30 Everett, WA
1/2 the voltage will be 1/4 the wattage. In addition the amount of light from an incandescent bulb is not linear. I don't think you can easily calculate the amount of light with reduced voltage. Just get the appropriate bulb unless you are using it for a tiny heater.
 
Ken Cross

Ken Cross

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Oct 24, 2010
2,405
Hunter 30 Everett, WA
Sorry I said that wrong

Ken Cross said:
1/2 the voltage will be 1/4 the wattage. In addition the amount of light from an incandescent bulb is not linear. I don't think you can easily calculate the amount of light with reduced voltage. Just get the appropriate bulb unless you are using it for a tiny heater.
Click to expand
Based on a constant resistance the power would be 1/4 with 1/2 voltage, but the resistance of an incandescent bulb changes with current due to temperature changes in the bulb. That makes calculations more difficult.
 
C

Chief RA

.
Nov 26, 2012
2,315
Catalina 250 Bodega Bay CA
Ken: the wattage value varies inversely with the impedence, it is not a fixed ratio. Chief
 
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