Resistor for daytime running lights?

I'm creating a daytime running light with a relay. I know that doing it this way, I will get 100% headlight output, making it just the same as if the headlights were turned on. Can I somehow lower this output by using a resistor? If yes, then which resistor should I use? And is it safe with no side effects?

You could always wire the lights in series.

Each will get only half of the voltage and they will be half as bright.

Positive + ----O----O---- Negitive -

                     L1     L2

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

John, you are usually right on, but in this case I think the lights will be nowhere near half the output, much less 'bright'
Headlamps decrease output at an exponential rate (~3.4), and brightness is the square of that. The image below is based on a 9006 headlamp, most US-Spec'd lamps are rated similiarly

What was a popular way for the mfr at one time was to use the voltage drop across 2 diodes to decrease the voltage. A couple of bucks at rad-shack can get you a full wave bridge rectifier which can be configured to do this- just hook the dc+ to the 12V side and the headlamp to the dc- terminal. Dropping 1.5v will cut you down to ~50% brightness

some source information:
Daniel Stern Lighting