Signal lights in cars

Signal lights have an important safety function. They demonstrate deceleration and a change in direction of the vehicle, and make the vehicle more visible to other road users when it is dark or during poor visibility. On this page, you can find out how signal lights are structured, and what technology is behind new signal systems. Here you can also find the most common causes of failure for signal lights, tips for troubleshooting, and information regarding important regulations.

The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for suitably qualified personnel only.

Car indicator signal lights

Exterior lights – whether attached at the front, side or rear of the vehicle – provide information for other road users through their signals and are thus responsible for safety on the roads to a substantial extent.

Signal light: Section through an automotive light — Section through an automotive light: 1 Bulb holder, 2 Reflector, 3 Cover lens with optics, 4 Seal, 5 Bulb, 6 Vehicle body

A conventional passenger car signal light basically consists of three assemblies: The bulb holder, the housing, and the cover lens.

The bulb holder positions one or more light sources correctly in relation to the optical system of the light.
The housing contains the reflectors which are usually molded.
The cover lens is responsible for light distribution through additional patterned structures.

In order to meet the photometric requirements, the light from the light sources has to be collected and directed, deflected, and distributed. Several optical component parts are used for this purpose.

Signal lights: Optical systems with bulbs — Optical systems with bulbs

Asignis® – Adaptives Signal-system

Adaptive Signal System: BMW rear light, stop light

Adaptive Signal System: BMW rear light, direction indicator

All the functions in a rear light only work on one brightness level, no matter whether they are switched on during the day, at night, or on a bright foggy morning. The only current possibility of adapting the lights to adverse weather conditions is the rear fog light. This is often used incorrectly, however, and leads to irritation. There is no additional information conveyed about whether the brakes are only being applied lightly or slammed on, for example.

Thanks to ASIGNIS®, the individual signal lights in a rear combination lamp (brakes, direction indicator etc.) can be adapted to the current situation. Depending on weather and visibility conditions the light intensity of the signals (e.g. brighter during the day and darker at night or with the braking signal) can be varied.

The requirement for differing braking signals can either be met by means of a larger signal area, an increase in brightness, or the addition of an increased flashing frequency. The stop light is activated in three stages dependent on deceleration: The greater the deceleration, the more LEDs light up. In the case of a hard stop, one part-array of the red stop light flashes as an additional warning function.

Tips for dealing with signal lights

In many vehicles, the light sources are controlled via pulse width modulation (PWM). This has several advantages for the vehicle lighting. For one thing, the same bulbs can be used for different functions, and the service life of the bulbs is increased.

The rear lamps of the Golf V also use PWM. PWM allows the use of a 21 W bulb both for the stop light and for the tail light. The pulse width is modulated in such a way that the 21 W bulb has almost the same luminous flux as a 5 W bulb. If the brake is now actuated, the turn-on time is so long, that 13.5 V is present at the stop light, and the 21 W bulb provides the full luminous flux (see illustration). Once the brake is released again, the voltage returns to 5.74 V.

When replacing bulbs in signal lights, the information and specifications of the manufacturer must always be adhered to. If an incorrect bulb is used, there is the danger that the required luminous intensity will not be reached.

Signal light regulations

Due to the scope of the statutory regulations, only the most important are explained here. The following regulations contain all the relevant information about signal lights, their properties, and uses:

76/759/EEC, ECE-R6, StVZO § 54
Direction indicators front, rear, and side

76/758/EEC, ECE-R7, StVZO §§ 51 and 53
Marker lights and tail lights front and rear

77/540/EEC, ECE-R77, StVZO § 51
Parking lights front and rear

ECE R87
Daytime running lights

77/539/EEC, ECE-R23, StVZO § 52
Reversing lights

76/758/EEC, ECE-R7, StVZO § 53
Stop lights

77/538/EEC, ECE-R38, StVZO § 53d
Rear fog lights

76/760/EEC, ECE-R4, StVZO § 60
License plate lamps

ECE R3
Reflex reflectors

Direction indicators front, rear, and side
Number at the front	Two
Number at the rear	Two or four
Number at the side (optional)	One per side
Colour	Amber
Height position	Between 350 mm and 1500 mm permissible
Width position
Side position	Installation height between 350 mm and 1500 mm and max. 1800 mm from the front edge of the vehicle
Electrical circuit	An electronic warning flasher unit is made up of a pulse generator which switches the lights on via a relay. In addition, it also has a control circuit which is dependent on current and changes the flashing frequency in the event of light failure. The frequency of the flashing signals is between 60 and 120 per minute. All the direction indicators on the same side of the vehicle have to work synchronously.
Switch-on control	Green indicator lamp
Miscellaneous	Depending on the requirements, there are different functional controls for monitoring the indicator system (single-circuit, dual-circuit control).

Marker lights (passenger vehicles) front
Number	Two or four
Colours	White, or amber when main headlamps are amber
Mounting	The arrangement is the same as for the front direction indicators.
Miscellaneous	Vehicles and trailers over 1600 mm wide require marker lights (to the front).

Tail lights
Number	Two or four
Colour	Red
Height position	Between 350 mm and 1500 mm permissible
Width position	Max. 400 mm from the outermost edge of the body. At least 600 mm apart
Electrical circuit	No particular specifications
Miscellaneous	In the event of dual function (stop and tail light), the luminous intensity ratio of the individual functions must be at least 5 to 1.

Rear fog lights
Number	One or two
Colour	Red
Height position	Between 250 mm and 1000 mm permissible
Width position	The distance to the stop light must be at least 100 mm.
Electrical circuit	Rear fog lights may only work when low beam, high beam, or fog lamps are switched on. They must be able to be switched off independently of the fog lamps.
Switch-on control	Amber, vehicles approved before 1981 also green
Miscellaneous	The visible illuminated area must not be more than 140 cm2. The light may only be switched on when visibility is less than 50 m.

Rear fog lights
Number	One or two
Colour	Red
Height position	Between 250 mm and 1000 mm permissible
Width position	The distance to the stop light must be at least 100 mm.
Electrical circuit	Rear fog lights may only work when low beam, high beam, or fog lamps are switched on. They must be able to be switched off independently of the fog lamps.
Switch-on control	Amber, vehicles approved before 1981 also green
Miscellaneous	The visible illuminated area must not be more than 140 cm2. The light may only be switched on when visibility is less than 50 m.

License plate lamps
Number	Depending on requirements one or two lamps
Colour	White
Mounting	No particular specifications
Electrical circuit	No particular specifications
Switch-on control	Amber, vehicles approved before 1981 also green
Miscellaneous	The rear license plate must be illuminated in such a way that it can be read at a distance of 25 m. The minimum luminance of the complete surface area must be at least 2.5 cd/m2.

Reversing lights
Number	One or two
Colour	White
Height position	250 to 1200 mm permitted
Width position	No particular specifications
Electrical circuit	The circuit only works with the ignition switched on and the reverse gear engaged.

Parking lights
Number	Depending on requirements two at the front and two at the rear or one at each side
Colour	White
Height position	Between 350 mm and 1500 mm permissible
Width position	Max. 400 mm from the outermost edge of the body. At least 600 mm apart
Electrical circuit	The parking lights must be able to work without other lamps being switched on.
Switch-on control	Amber, vehicles approved before 1981 also green
Miscellaneous	The parking light function is usually taken over by the tail lights.

Side marker lights
Number	Depending on the length of the vehicle
Colour	Amber
Height position	Between 250 mm and 1500 mm permissible
Width position	Max. 3000 mm from the front edge of the vehicle and max. 1000 mm from the rear edge of the vehicle
Electrical circuit	No particular specifications

Daytime running lights
Number	Two at the front
Colour	White
Height position	Between 250 mm and 1500 mm permissible
Width position	Max. 400 mm from the outermost edge of the body. At least 600 mm apart
Electrical circuit	The daytime running lights must switch off automatically if the low-beam headlamps are switched on.

Installation regulations side view

Installation regulations rear view

Type approval numbers on signal lights

National and international design and operating regulations apply for the manufacture and testing of vehicle lighting equipment. Special approval marks exist for signal lights and can be found on the light.

One example
The following can be found on a light RS1 IAF 02 E1 Æ 31483:

R stands for tail light,
S1 for stop light,
IA for reflex reflector,
F for rear fog light and 02 means that the regulation has been revised twice since publication.

These features are integrated in the rear combination lamp:

The E1 marking means that the light has been approved in Germany.
The arrow shows which way the light can be installed and therefore always points to the outer edge of the vehicle. If there is no arrow on the light it can be installed at the right or left rear side.
The five-digit number at the end is the type approval number.

Help in decoding the combinations of numbers and letters on signal lights

A Marker light
AR Reversing light
F Rear fog light
IA Reflex reflectors
R Tail light
S1 Stop light
1 Front direction indicator (different technical design)
1a Front direction indicator (different technical design)
1b Front direction indicator (different technical design)
2a Rear direction indicator
5 Additional side direction indicator (for vehicles up to 6 m in length)
6 Additional side direction indicator (for vehicles longer than 6 m)
SM1 Side marker light (for all vehicles)
SM2 Side marker light (for vehicles up to 6 m in length)

The permissible luminous intensity values vary depending on the function. Changes in movement (braking = 60 cd) have a stronger lighting signal than those for position and orientation (tail light = 4 cd).

S Tail light
B Stop light
ZB Additional stop light
BL Direction indicator light
ZR Tail light
NES Rear fog light
PO Position light