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Are flashing bike lights legal in California?

Short answer: No, but you’re probably not going to get in trouble for using them.

bike light on handlebars

I light up the front of my Schwinn Coffee with a Planet Bike Blaze model two watt light with superflash.

On my ride home from work the other day, I passed a disheveled looking man on a bicycle (riding on the against-traffic side on the sidewalk1, at dusk, without a light, a helmet, or proper reflectors). As I passed him, he remarked about my flashing white light, “Those flashing lights are illegal!”

As you might have gathered from previous posts on this website, I am extremely critical of those who don’t follow the letter of the law. As I approached him, my mind was cataloging all of his grievous safety violations, so when he blurted out his criticism of my adherence to the rules, all I could muster was a, “No it’s not.”

But was it? I had never actually read that it wasn’t. I do read the DMV driver’s handbook every year, and I have read the California vehicle code for cyclists many times, but I honestly couldn’t remember reading anything about flashing lights. So I looked it up.

California Vehicle Code Division 11 Chapter 1 Article 4 Section 21201 (d) covers the requirements for cyclists when riding in darkness. It states:

A bicycle operated during darkness upon a highway, a sidewalk where bicycle operation is not prohibited by the local jurisdiction, or a bikeway, as defined in Section 890.4 of the Streets and Highways Code, shall be equipped with all of the following:

(1) A lamp emitting a white light that, while the bicycle is in motion, illuminates the highway, sidewalk, or bikeway in front of the bicyclist and is visible from a distance of 300 feet in front and from the sides of the bicycle.

(2) A red reflector on the rear that shall be visible from a distance of 500 feet to the rear when directly in front of lawful upper beams of headlamps on a motor vehicle.

(3) A white or yellow reflector on each pedal, shoe, or ankle visible from the front and rear of the bicycle from a distance of 200 feet.

(4) A white or yellow reflector on each side forward of the center of the bicycle, and a white or red reflector on each side to the rear of the center of the bicycle, except that bicycles that are equipped with reflectorized tires on the front and the rear need not be equipped with these side reflectors.

This portion of the vehicle code says nothing specifically about flashing lights, but the intended purpose of requiring a front light seems to be three-fold: 1) to be visible by other vehicles at a minimum distance of 300 feet, 2) to illuminate the bikeway in front of the cyclist, 3) and (by specifying white light) to signify in which direction the cyclist is traveling.

A flashing white light clearly meets two of these criteria, but I could see where one may question whether or not the flashing light adequately illuminates the path in front of the cyclist. Obviously, this can vary depending on your light. My light has two brightness settings and makes use of both in flash mode: a single bright flash, followed by three or four (it’s too fast to really tell) dimmer flashes. The frequency of these flashes is sufficient enough to light my way in darkness, although I never use this setting in complete darkness.

Dusk and dawn are the most dangerous times to be on the road. These are the hours when most people are traveling to and from work, which means they tend to be in more of a hurry, and driving on roads they frequent which makes them less likely to be focused. To make matters worse, visual contrast is at its lowest during these hours. The sun is below the horizon, but still illuminates enough of the atmosphere to light the road, making the use of headlights a questionable necessity for most vehicles. These are the hours I use my flashers, and these were the conditions when I encountered the disheveled sidewalk cyclist.

The California Vehicle Code doesn’t specifically mention flashing lights in this context, so one must presume that if a white flashing light adequately illuminates your path and is visible at 300 feet, it meets the requirement for the law; just as a steady light that does not sufficiently light your path or is not visible at 300 feet does not meet the requirement for the law.

If flashing lights are illegal, there must be another reason. Perhaps it is a distraction to drivers. But where would one draw the line between visibility and distraction? Emergency vehicles use flashing lights specifically for the purpose of calling attention to themselves—one of the requirements for using a bike light. Maybe they want to reserve the use of flashing lights for emergency vehicles. Does the CA Vehicle Code say anything about flashing lights as they pertain to emergency vehicles? Yes!

21201.3.  (a) A bicycle or motorized bicycle used by a peace officer, as defined in Section 830.1 of, subdivision (a), (b), (c), (d), (e), (f), (g), or (i) of Section 830.2 of, subdivision (b) or (d) of Section 830.31 of, subdivision (a) or (b) of Section 830.32 of, Section 830.33 of, subdivision (a) of Section 830.36 of, subdivision (a) of Section 830.4 of, or Section 830.6 of, the Penal Code, in the performance of the peace officer's duties, may display a steady or flashing blue warning light that is visible from the front, sides, or rear of the bicycle or motorized bicycle.

(b) No person shall display a steady or flashing blue warning light on a bicycle or motorized bicycle except as authorized under subdivision (a).

Flashing blue lights are illegal unless you are a peace officer on duty. My light is white. We’re getting closer.

Searching the California Vehicle Code for “Flashing Lights,” I found Section 25250 on Flashing Lights:

Flashing lights are prohibited on vehicles except as otherwise permitted.

Well that sounds pretty clear. Do bicycles count as “vehicles,” and what do they mean by “otherwise permitted?”

California Vehicle Code Section 670:

A “vehicle” is a device by which any person or property may be propelled, moved, or drawn upon a highway, excepting a device moved exclusively by human power or used exclusively upon stationary rails or tracks.

My bike is moved exclusively by human power. It therefore is not considered a vehicle. If I were to have electrical assist, however, I suppose I would fall into the vehicle definition.

If my human–powered bike is not considered a vehicle, though, why does the vehicle code even apply to me at all? The vehicle code even having sections pertaining to human–powered bicycles at all clearly contradicts section 670.

Regardless of whether or not we are technically considered vehicles, we are indeed subject to the same rules. 

California Vehicle Code Section 21200 (a):

A person riding a bicycle or operating a pedicab upon a highway has all the rights and is subject to all the provisions applicable to the driver of a vehicle by this division, including, but not limited to, provisions concerning driving under the influence of alcoholic beverages or drugs, and by Division 10 (commencing with Section 20000), Section 27400, Division 16.7 (commencing with Section 39000), Division 17 (commencing with Section 40000.1), and Division 18 (commencing with Section 42000), except those provisions which by their very nature can have no application.

For all intents and purposes, bicycles count as vehicles. So what is this otherwise permitted business from section 25250?

California Vehicle Code Section 25251 Permitted Flashing Lights:

(a) Flashing lights are permitted on vehicles as follows:

(1) To indicate an intention to turn or move to the right or left upon a roadway, turn signal lamps and turn signal exterior pilot indicator lamps and side lamps permitted under Section 25106 may be flashed on the side of a vehicle toward which the turn or movement is to be made.

(2) When disabled or parked off the roadway but within 10 feet of the roadway, or when approaching, stopped at, or departing from, a railroad grade crossing, turn signal lamps may be flashed as warning lights if the front turn signal lamps at each side are being flashed simultaneously and the rear turn signal lamps at each side are being flashed simultaneously.

(3) To warn other motorists of accidents or hazards on a roadway, turn signal lamps may be flashed as warning lights while the vehicle is approaching, overtaking, or passing the accident or hazard on the roadway if the front turn signal lamps at each side are being flashed simultaneously and the rear turn signal lamps at each side are being flashed simultaneously.

(4) For use on authorized emergency vehicles.

(5) To warn other motorists of a funeral procession, turn signal lamps may be flashed as warning lights on all vehicles actually engaged in a funeral procession, if the front turn signal lamps at each side are being flashed simultaneously and the rear turn signal lamps at each side are being flashed simultaneously.

(b) Turn signal lamps shall be flashed as warning lights whenever a vehicle is disabled upon the roadway and the vehicle is equipped with a device to automatically activate the front turn signal lamps at each side to flash simultaneously and the rear turn signal lamps at each side to flash simultaneously, if the device and the turn signal lamps were not rendered inoperative by the event which caused the vehicle to be disabled.

(c) Side lamps permitted under Section 25106 and used in conjunction with turn signal lamps may be flashed with the turn signal lamps as part of the warning light system, as provided in paragraphs (2) and (3) of subdivision (a).

(d) Required or permitted lamps on a trailer or semitrailer may flash when the trailer or semitrailer has broken away from the towing vehicle and the connection between the vehicles is broken.

(e) Hazard warning lights, as permitted by paragraphs (2) and (3) of subdivision (a) may be flashed in a repeating series of short and long flashes when the driver is in need of help.

So there you have it. A person riding a bicycle on a highway is subject to the same provisions as a person driving a vehicle, and vehicles are prohibited from using flashing lights (accept in those cases outlined above).

In practice, it seems to me that it is likely safer to use flashing lights on your bike in situations where your path is clearly visible, but your visibility to others might be low—such as during dusk, dawn, rain, or fog. Because something seems likely does not necessarily mean it is likely, however—and that’s why we have science!

I’ll likely be looking into the other bicycle-friendly cities and see if they have any actual data on flashing lights vs. steady lights in the twilight hours. In the mean time, I will not be using flashers.

To the disheveled sidewalk bicyclist I say: You are right! And please don’t ride on the sidewalk. It’s dangerous and illegal in the central traffic district of Woodland, California.


  1. Woodland, CA Municipal Code Section 5.19 states that it is illegal to ride a bicycle on the sidewalk in the central traffic district. Our encounter was well within the central traffic district.