I've been a fan of the unique non linear properties of lamps. Lamps have been used since the early days of electronics to stabilize amplifiers and oscillators. A couple years back, I had to build a piece of production test equipment that had could produce and switch a millivolt level that was exactly the same for DC and RMS. No fancy electronics, just resistors and a lamp in a bridge circuit. From 90-130V input the output varied less than 0.25%. The test results may help you understand strange results when lamps are used as load resistors. The following are the results of a test with a new #1156 auto lamp and the calculated resistance.
- V 2.29A 6.1 ohm
- V 2.20A 5.9 ohm
- V 2.11A 5.7 ohm
- V 2.02A 5.4 ohm
- V 1.92A 5.2 ohm
- V 1.83A 4.9 ohm
- V 1.72A 4.7 ohm
- V 1.61A 4.3 ohm
- V 1.49A 4.0 ohm
- V 1.36A 3.7 ohm
- V 1.23A 3.3 ohm
- V 1.08A 2.8 ohm
- V 0.91A 2.2 ohm
- V 0.71A 1.4 ohm
- 5V 0.55A .91 ohm
Of interest is the voltage range of 0.5V to 5V witch approximates the differences between a battery and an open circuit 12V solar panel. While the voltage increases ten times, the current only increases 2 ½ times. While not exactly constant current, the changes in current from low to high light conditions are greatly reduced. This could be useful to those that have a minimal system with no controller and want to maintain a charge when gone for long periods. When used with a zener to protect electronics, a wider voltage range can be accommodated with lower power dissipated. For an 11-14V increase of 27%, the current only increases 13%. Hope this gives you some ideas for new uses. These results are typical for other lamps of different currents.
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