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  • norwegr Tuesday, December 05, 2017 5:49 AM Reply

    Are these dimmable?

    Will the dimmer in the car work the same on these led buls as on old incandescent bulbs?

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  • Maye_Tao Thursday, December 07, 2017 11:10 AM Reply


    They are not dimmable.

    Be happy. ( *^_^* )
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  • norwegr Saturday, December 09, 2017 6:36 AM Reply

    Are you certain? All instrument lights in cars are dimmable, either automatic or manual, or a combination. These bulbs are obviously made for use as instrument lights, and such LEDs sold elswhere are dimmable. Anything else is pointless. (Can't drive in the dark in the country-side if the instrument lights are at full blast. You wouldn't see the road)

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  • Maye_Tao Saturday, December 09, 2017 9:19 AM Reply



    Be happy. ( *^_^* )
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  • ebpDoug Saturday, December 09, 2017 9:43 AM Reply

    For some reason this forum entry isn't showing me the product in question, but I had noted your question previously. As I recall, the LEDs were quite low power - a fraction of a watt.

    It is very likely that the lamps are simply a LED in series with a resistor, rather than a LED with a constant-current driver of some sort. LEDs with resistors can be dimmed. A dimmer circuit that varies the voltage will work. So will one which uses pulse width modulation (either zero volts or full voltage is applied to the lamp & the proportion of the time that full voltage is applied to the period determines effective brightenss e.g. on for 2 milliseconds, off for 3 milliseconds gives the equivalent of 40% of what you would get with continuously-on). What isn't likely to work is the dimmer in an old car from the days before electronic controls. A simple rheostat (variable resistor) in series with the lamps was common. This won't work well with LED lamps because it relies on the relationship between lamp resistance and rheostat resistance to vary the effective voltage applied to the lamps. LEDs would be much much higher in resistance than incandescent lamps, so the effect of the rheostat would be minimal (i.e. almost no dimming). Unless you are retrofitting a '57 Chevy, you aren't likely to run into this (I don't really know when electronic dimmers became common - I'm guessing in the 70s or 80s).

    If you take out one panel lamp in your car and the others don't change in brightness, chances are the LEDs will work. If the others get brighter, the LEDs are very unlikely to work.

    Higher power LEDs lamps are likely to have constant-current drivers. Typically the brightness will stay constant as the input voltage is reduced, down to the point where the driver can no longer maintain current. Some constant current drivers will work well with pulse width modulated input, some won't.

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