let me see if i got it, as the voltage goes down so does the heat, and

the cooler it is the less resistance it has, so it pulls less amps.

this decrease in power makes for dimmer light. Do i have it figured out?

Actually, pulling less amps is from less voltage.

If resistance is constant, then amps pulled is volts divided by the

resistance.

But with a lightbulb, resistance decreases as voltage decreases, so as

voltage decreases the amps go down less than they would if the resistance

did not change.

A 100 watt 120V lightbulb has a resistance of 144 ohms at 120V.

According to Ohm's Law:

I=E/R, I=120/144, which is .833 amp

But apply various voltages to a hypothetical ideal 144 ohm resistor and

an actual 100 watt lightbulb:

(Figures for the lightbulb at voltages less than 120V I am predicting

based on what I know about them, and are mostly interpolations along with

two extrapolations and are not actual measurements except 9.3V and 11.2V

which are actual measurements.)

(ALSO please note that a 144 ohm 100 watt resistor whose resistance is 144

ohms both cold and at full power operating temperature is a hypothetical

item - I have yet to see this in any electronics parts supplier's

catalog! Please also note that 144 ohms is not even a standard resistor

value but 100, 120 and 150 ohms are standard resistor values, and

resistors of wattage rating more than 10 watts are less common and less

standardized than ones rated 10 watts or less!)

VOLTAGE RESISTANCE of RESISTANCE of CURRENT thru CURRENT thru

144 ohm resistor 100W 120V lamp 144 ohm res. 120V 100W lamp

--------------------------------------------------------------------------

120 V 144 ohms 144 ohms .833 amp .833 amp

100 V 144 ohms 131.5 ohms .6944 amp .76 amp

80 V 144 ohms 117.6 ohms .5556 amp .68 amp

60 V 144 ohms 102 ohms .41667 amp .59 amp

50 V 144 ohms 93 ohms .347 amp .54 amp

40 V 144 ohms 83 ohms .2778 amp .481 amp

30 V 144 ohms 71.9 ohms .20833 amp .417 amp

24 V 144 ohms 64.2 ohms .1667 amp .374 amp

20 V 144 ohms 58.5 ohms .1389 amp .342 amp

15 V 144 ohms 50.5 ohms .1041557 amp .297 amp

12 V 144 ohms 45.3 ohms .0833 amp .265 amp

11.2 V 144 ohms 43.9 ohms .0777 amp .255 amp

10 V 144 ohms 40.8 ohms .069444 amp .245 amp

9.3 V 144 ohms 38.8 ohms .0646 amp .24 amp

6 V 144 ohms 31 ohms .041667 amp .193 amp

..1 V 144 ohms 9.7 ohms .6944 mA 10.3 mA

Hope this helps,

- Don Klipstein (

[email protected])