Rear fog lights

[jwight]

Still seems to be some confusion on this so here's some info from Wikipedia:

Rear fog lamps

(ECE Regulation 38, SAE J1319)

In Europe and other countries adhering to ECE Regulation 48, vehicles must be equipped with one or two bright red "rear fog lamps" (or "fog taillamps"), which are switched on manually by the driver in conditions of poor visibility to enhance vehicle conspicuity from the rear. The allowable range of intensity for a rear fog lamp is 150 to 300 candelas, which is within the range of a U.S. brake lamp. For this reason, many European vehicles imported to the United States have their rear fog lamps wired as brake lamps, since their European-specification brake lamps may not be sufficiently intense to comply with U.S. regulations, and in North America rear fog lamps are not required equipment. However, they are permitted, and are found almost exclusively on European-brand vehicles in North America — Audi, Jaguar, Mercedes, MINI, Range Rover, Saab and Volvo provide functional rear fog lights on their North American models. The final generation Oldsmobile Aurora also had dual rear fog lights installed in the rear bumper as standard equipment.

Most jurisdictions permit rear fog lamps to be installed either singly or in pairs. If a single rear fog is fitted, most jurisdictions require it to be located at or to the driver's side of the vehicle's centreline — whichever side is the prevailing driver's side in the country in which the vehicle is registered. This is to maximise the sight line of following drivers to the rear fog lamp. If two rear fog lamps are fitted, they must be symmetrical with respect to the vehicle's centreline. Proponents of twin rear fog lamps say two lamps provide vehicle distance information not available from a single lamp. Proponents of the single rear fog lamp say dual rear fog lamps closely mimic the appearance of illuminated brake lamps (which are mandatorily installed in pairs), reducing the conspicuity of the brake lamps' message when the rear fogs are activated. To provide some safeguard against rear fog lamps' masking of brake lamps, ECE R48 requires a separation of at least 10 cm between the closest illuminated edges of any brake lamp and any rear fog lamp.

Note that the rear fogs will be about the intensity of rear brake lights when activated, or much brighter than the normal intensity of red tail lights.

[rollingtones]

US regulations state that tail lamps be 4W (4 Watts) each, while brake, turn signals and rear fog lamps, if fitted, be 21W (21 Watts) each.

Having the 4 watt and 21 watt figures in your head allows you to get a feel for the difference in brightness.

[jwight]

Good info; do you have the source 'cause I couldn't find anything that specific. Thanks.

OK, I didn't get into the bulb portion:

Incandescent light bulbs

Traditionally, an incandescent tungsten light bulb has been the light source used in all of the various automotive signalling and marking lamps. Typically, bulbs of 21 to 27 watts, producing 280 to 570 lumens (22 to 45 Mean Spherical Candlepower) are used for brake, turn, reversing and rear fog lamps, while bulbs of 4 to 10 W, producing 40 to 130 lm (3 to 10 mscp) are used for tail lamps, parking lamps, sidemarker lamps and side turn signal repeaters.