Flood beam
Also called wide beam, diffused beam, flood pattern, flood light
A flood beam is a wide off-road light pattern, often forty degrees or more across, that fills the near ground and the sides at the cost of distance, and it belongs low because a wide beam lights a lot of air close to the vehicle.
What is a flood beam?
It is the same light spread over a much larger area. Where a spot concentrates output into a narrow cone to reach a long way, a flood opens the cone up and gives up the reach in exchange for width. Nothing is created or destroyed: the optics decide the trade.
That makes it the right pattern for slow and technical driving, where what you need is to see the ground either side of the tires, the rock you are about to place a wheel on, and the trail edge. It is the wrong pattern for speed, because at forty miles an hour you are outdriving it.
Why a flood belongs low
A wide beam lights a large volume of air near the vehicle, and near the vehicle is exactly where your line of sight passes. Put that volume at eye level and in dust or fog you are looking through a bright wall. Put it below your eyes and you are looking over the top of it at ground that is lit.
This is why the lamp makers put their wide patterns on the bumper. Baja Designs specify their dust and fog, cornering and driving zones low, and recommend that eighty percent of a lighting package stays below the hood line. A sharp upper cutoff makes a wide beam much better behaved in bad air, but it does not license mounting one high.
See also
Seen in
Sources
- Lighting Zones 1 to 5, Baja Designs, read 2026-08-27Read across the set. Zone 2 https://www.bajadesigns.com/help/lighting-zones/zone-2-cornering/, Zone 3 https://www.bajadesigns.com/help/lighting-zones/zone-3-driving-combo/, Zone 4 https://www.bajadesigns.com/help/lighting-zones/zone-4-spot/, Zone 5 https://www.bajadesigns.com/help/lighting-zones/zone-5-racer-edition-spot/.
- SAE J387, Terminology, Motor Vehicle Lighting, 1987 revision, SAE International, reproduced by Public.Resource.Org, read 2026-08-27Free in full because this revision was incorporated by reference into US federal law, and read in full by us. It is an SAE Information Report, not a standard, and it defines ten terms: bulb, lamp, light, device, unit, accurate rated bulb, centroid of a lens area, multiple compartment lamp, optically combined and multiple lamp arrangement. It defines no beam pattern of any kind, so it does not weigh against spot or flood specifically. Later revisions are paywalled. J581 Auxiliary High Beam Lamps (https://saemobilus.sae.org/standards/j581_201102-auxiliary-high-beam-lamps) and J583 Front Fog Lamp (https://saemobilus.sae.org/standards/j583_202005-front-fog-lamp) are the two beam-pattern standards, and we have not read either. The reason they are not free is itself informative: we searched the FMVSS incorporation-by-reference list at 49 CFR 571.5 (https://www.ecfr.gov/current/title-49/section-571.5) and neither appears in it. FMVSS 108 incorporates six SAE documents, covering bulb sockets, lamp bulbs, headlamp aiming, driver eye range and discharge forward lighting, and no driving-lamp or fog-lamp standard among them. That is the FMVSS list specifically; we make no claim about other US regulations.