Sizing transistors for linear operation will become very expensive. Because with higher voltage than about 3..4V across the FET, the allowed current droops very rapidly, usually ~1/Vds^2. The problem is, the FETs do suffer from thermal instability over their silicon area in a similar manner as bipolars do. Claims like "FETS do not suffer from second breakdown" is not true anymore, once the FETs reached the low Ron and so the high current capabilities. It is displayed in the SOA chart...

With the pulsing it is worse than a single pulse, but still tolerable. The point is that way it allows to use transistor way smaller than would be needed to drive the full cold lamp current (about 14x the nominal), yet stay within the safe operating area of the transistors. Mainly when integrated into some more complex IC (one chip driving a bunch of bulbs and so on, where the silicon area (needed fot brutt force power) is way more expensive than discrete transistors, but the density of small transistors allow to integrate way more complex control into fraction of the power element on the chip. Or whenlarge currents are involved, so a microcontroller alowing the more complex scheme is cheaper than the brute force power transistor sizing.

Such warmup burst uses to be some dozen of pulses, so not that much stress from the battery ripple. But having similar thing present all the time could wear the input connections (reverse battery protections and the input capacitors in many of the electronic modules). Plus it may affect many sensors, temporary burst of inaccurate data from the sensors could be ignored (the car electronics count on such starting bursts happening from time to time), but for longer time would cause problems (may trigger fault codes, so they should not las for so long).

The alternator has no problem at all, as it won't respond that quickly anyway, such surges are handled solely by the battery. The alternator only takes over the average current, just maintaining the battery charge level balance...

Using high frequency DCDC means way more complicated and demanding power circuit, you need to put all the smoothing within the control box. Way too much hassle for something as slow as an incandescent.

Both Philips and Ledvance's >90 CRI lines have great light quality. Osram/Ledvance also offer 2400 or 2500k extra warm white, >90 CRI lamps which make dimly lit rooms extra cozy.
All are quite efficient, but practically all leds are these days anyway - i don't care whether a lamp uses 5w or 10w because either is negligible on my electricity bill, compared to the cost of running a washing machine.

Avoid those 210lm/w 80cri filament lamps (aka dubai lamps). Those have a very bad color shift to greenish yellow.

Can't say much about longevity. That's lab test stuff, you'd need to test hundreds if not thousands of lamps to get a realistic impression of failure rates. So far, i have only had 1 or 2 LED lamps die in about 10 years of using various ones.

In what parameter ?

Light quality (for anything that resembles white light) - None of them

Longevity and reliability - Something DIY with big derating for all LEDs and driving components. (It does not have to be complex, even "capacitive dropper" can be made to last for decades with correctly chosen components)

If not DIY, for ordinary screw base lamps, the runner up's for reliability would be probably something that looks like the oldest LED lamps with the big exposed heatsinks, or low power (<=2W) filament lamps, or generally anything that looks abnormally large for its power rating regardless of shape

But the driver failures (for non DIY lamps) are harder to predict and can happen anytime in any lamp

If you are paralleling, put some 4 IXFN520N075T2 ($34 each) in parallel and you'll be able to soft start the lamp with the original linear circuit proposed.....



But i have another question about the "hiccup" start :

The whole question about soft starting was to reduce the effects of load transient on the alternator. Which i can understand as 2 effects :
 - The electrical brownout that will result from the essentially brief short circuit
 - The mechanical braking momentum, which could maybe lead to as much as a momentary belt slip ?

We are still talking about "hard" PWM on the car electrics here

Could the "hiccup" start (so pulsing the lamps on and off multiple times before they heat up) potentially be worse for the car electrics than a single event ?

 - The main filtering capacitors in the input of electronic devices will probably deal better with a few short brownouts (with recharging time between them) than 1 long brownout

 - But won't the repeated brownouts cause potentially more interference in other ways ?



Consider that with the addition of an inductor and diode, this circuit becomes a complete buck converter that can do all startup and dimming functions with no restrictions....

The magnetics will be a bit huge for low frequency, but probably a sensible frequency can be chosen to make it work

Or go back to the resistors, first connect through resistor limiting to 3x...5x In, then (after fixed time delay) to full 12V

Where do you came to the 10V?
Cold filament resistance of a 250W 12V halogen is about 40m Ohm, with 14V battery the current will be about 350A (neglecting wiring resistances). With a 1m Ohm MOSFET, so voltage drop on it will be about 0.35V.
With 6mm^2 5m long wires there will be another 14m Ohm, so we are at about 260A and 0.26V across the MOSFET.

Given the SOA of even a single FET, we are just fine - staying on the left "Ron" limit line (the voltage is dictated by the device Ron). And because I would expect at least 2 or 3 in parallel, we are talking about 80A or 130A for each MOSFET at the Ron line.

Yes, a short circuit may exceed the limit for just two in parallel for DC, but there the decisive factor is the fuse characteristic, where for a 30A fuse the break time is about 20ms for the slower fuse, while single transistor will withstand about 560A (calculated for the same i^2t when extrapolating from the "10ms" SOA). Using 3 transistors in parallel will bring the load way below the SOA...

The fixture R70.1 is very small in size. You only really get this impression when you see it mounted on a pole.

It was previously used in some small villages in the GDR. The photo shows a typical installation of this kind.

In October 2025, I photographed a fixture R70.1 that is still in use. This is a very rare situation in 2025.


Photo was taken in Westerhausen near Quedlinburg

Now imagine a well-burned-out HQL 80W or HQL 125W lamp, and you will have a rough idea of how much light still reaches the ground below.

Absolutely no way of doing this linear way with the parts suggested. May be possible with a group of more robust MOSFETs or by allowing some PWM.

@Medved, please consult SOA graph from the datasheet. Although the part looks robust, drain current is limited to just ~8A @ 10V!

10ms curve won't fit for sure, we are talking a massive filament with a long time constant here.

that's honestly interesting. I figured a soft ramp would be easier on electrical not harder. very well. hard start it is. less complicated anyway.

No need for the multiple postings.  I've added a comment under the photo.

None of them, except maybe the very earliest ones that were of reasonable quality.