| Word | Description |
| Ballast | An electrical device used in fluorescent and HID fixtures. It furnishes the necessary starting and operating characteristics to the lamp for proper performance. |
| Ballast Efficacy Factor (BEF) | Defined as ballast factor divided by input watts. The value is used to evaluate various lighting systems based on light output and power input. The BEF can only be used to compare systems operating the same type and quantity of lamps. |
| Ballast Factor (BF) | This is the percentage of a lamp's rated lumen output that can be expected when operated on a specific, commercially available ballast. Note that the "rated output" is sometimes measured on a reference ballast unlike ones that actually operate the lamp in the field. |
| Ballast Hum | Sound generated by the vibration of laminations in the iron core of the transformer or inductor present in the ballast. |
| Ballast Losses | Power or energy dissipated in the ballast as heat and not converted to lamp energy. |
| Base or Socket | The socket is the receptacle connected to the electrical supply; the base is the end of the lamp that fits into the socket. There are many types of bases used in lamps, screw bases being the most common for incandescent and HID lamps, while bipin bases are common for linear fluorescent lamps. |
| Base Temperature (Maximum) | The maximum operating temperature permitted for the base in Celsius. Fixture manufacturers need to ensure that these conditions are satisfied in their fixture. |
| Bayonett Base | A style of bulb base which uses keyways instead of threads to connect the bulb to the fixture base. The bulb is locked in place by pushing it down and turning it clockwise. |
| Beam Angle | The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 50% of maximum. The beam angle sometimes called "beam spread" is often part of the ordering code for the reflectorized lamps. Example: The 50PAR30/HIR/NFL25 is a 50 watt PAR30 narrow flood lamp with a beam angle of 25 degrees (See FIELD ANGLE). |
| Beam Lumens | The total lumens present within the portion of the beam contained in the beam angle. |
| Beam Spread (Approximate) | For reflector type lamps. The total angle of the directed beam (in degrees horizontal or vertical) to where the intensity of the beam falls to 50% or 10% of the maximum candlepower value as indicated. |
| Bi-Pin | Any base with two metal pins for electrical contact. This is the typical base for a fluorescent tube of 1 to 4 feet in length. It consists of 2 prong contacts which connect into the fixture. Medium bi-pins are used with type T-8 and T-12 tubular fluorescent lamps, and miniature bi-pins are used for tubular T-5 fluorescent lamps. Of course the Bi-Pin bulb is the standard connection for MR-16 bulbs. |
| Biax® | This is a GE trademark for GE's biaxial family of high-efficiency and long-life compact fluorescent lamps. A straight tube is bent back in the middle, constituting a biaxial tube. |
| Black Light | A popular term referring to a light source emitting mostly near UV (320 to 400 nm) and very little visible light. |
| Blacktop | Whether or not the top of the miniature lamp has a blacktop coating. The coating is used to control unwanted brightness or glare. |
| Bollard | A short, thick post with a light at its top, used for grounds and outdoor walkway lighting. |
| BTU | BTU or British Thermal Unit, is a unit of measure for heat value. The higher the BTUs a device is capable of outputting the more powerful it is. |
| Bulb | A common way of referring to a lamp. "Bulb" refers to the outer glass bulb containing the light source. |
| Bulb Material or Coating | The type of glass (or quartz) used in the glass envelope surrounding the light source. The material can also have coatings applied to achieve particular performances. |