PetrolDave wrote:Ahh, that's not what you said.adsgreen wrote:It's not the speed as such but the way they start up.
Conventional filament bulbs are very low resistance on start up when the element is cold, as they warm up to their running temperature the resistance increases - that's why if you measure the resistance of a cold bulb and do the P=V squared over R calculation it appears to be a much higher wattage than it actually is.adsgreen wrote:On a cold start the DIS is looking for very specific bulb activation behaviour and LED's trip this. After starting the DIS seems to be more forgiving.
LEDs normally have as high as possible a parallel resistor (to minimise heat and energy waste) and if this simulates the resistance of a warm bulb and not the cold resistance that will trigger the bulb failure warning.
as it heats up impedance increases...when cold nothing more than a coil (an inch or so) of wire, no resistance
it's not so much the inductance in this case but the thermal reaction of a tungsten filiment...proportional to temperature
the impedance Z of an inductor = jwL
j = sq rt -1
w = 2 Pi f (f = frequency)
l = inductance value, based on turns/windings, etc.
so as freq increases so does impedance, a cap reacts the exact opposite
since a car uses DC (0 freq) inductance is zip in a DC lamp filiment coil
a resistor is insensitive to freq (for normal ranges)
are you an EE?
