Dimensions: To accurately identify the size of your light bulb, take the maximum diameter of the glass portion and divide it by 8. An A21 bulb is 21/8 of an " in diameter, therefore it equals 2 5/8" diameter. G40 - 40/8" = 5" diameter. T12 - 12/8" = 1 1/2" diameter. PS30 - 30/8" = 3 3/4" diameter.

Length: Light Center Length (L.C.L) is the average measurement for which the lamp is designed, subject to manufacturing tolerances. The light center length is the distance from the center of light source to the following point for the base used: Screw bases > bottom base contact; Bayonet candelabra and medium bayonet > top of base pins; Single Contact or Double Contact Prefocus > Plane of locating bosses of prefocusing collar.

Maximum Overall Length (M.O.L.) is used to refer to the length of the entire bulb, from the tip of the glass to the bottom of the base.

Voltage/Measuring Light: Lamps that are listed as 115-125 volts (design voltage 120), 120-130 volts (design voltage 125), 125-130 volts, (design voltage 130) and 230-250 volts (design voltage240) are intended for use on circuits normally varying within these voltage limits. Lumens stands for total lamp light output. Candlepower (cp) indicates Ray of Light in one direction. Footcandles (fc) is calculated by taking the Maximum Beam Candlepower and dividing it by D squared.

Code Designations: The following code designations are used to identify the various colors/uses of incandescent light bulbs. W - white, Y - yellow, B - blue, R - red, G - green, A - amber, IC - iridescent clear, FL - flood, SP - spot, IF - inside frost, BL - blister packaging, AIC - amber iridescent clear, SPK - soft pink.

Filament Identification: A filament designation consists of a prefix letter to indicate whether the wire is straight or coiled, and a number to indicate the arrangement of the filament on the supports. Prefix letters include: C (coiled) -- wire is wound into a helical coil or it may be deeply fluted; CC (coiled coil) -- wire is wound into a helical coil and this coiled wire again wound into a helical coil.

Base Identification: Typical screw bases are displayed here. One lead-in wire is soldered to the center contact and the other is soldered or welded to the upper rim of the base shell. Base shells are typically made of brass or aluminum. ANSI designators are in parentheses.

Bulb Identification: A bulb designation consists of a letter(s) to indicate the shape and a figure(s) to indicate the approximate major diameter in eighths of an inch. Bulbs are measured through their greatest diameter in eighths of an inch. Thus, an F-15 bulb is a flame shape, 15/8 of an inch (or 1-7/8") in diameter.