Light Bulb Sizes and Shapes Explained

How Light Bulb Shapes Are Named

Light bulbs and lighting lamps are described by designated shape names and diameter/length codes. This usually takes a letter-number-letter format, though the last letter is optional. The leading letter(s) indicates the shape and the numbers indicate the diameter. (The final, optional letter can designate the length.)


Size is denoted by a number following the shape. In the US these numbers indicate the maximum diameter in eights of an inch. In other parts of the world this measurement is given in millimeters. For example the US bulb, R20 signifies a measurement of 20/8 or 2.5″ in diameter. Metric examples include the A19 which is a typical household incandescent light.



Sample LED Light Bulb Shape Designations:


    • (A) Standard household incandescent light bulb

       shape B Bulged bulb shape

    • (BT) Bulged or Blown Tubular bulb shape

    • (BR) Short reflector style light bulb

    • (C) Candle or Conical bulb shape

    • (CP) Crystalline Pear bulb shape

    • (E) Ellipsoidal bulb shape

    • (ER) Extended reflector light bulb shape F Flame style

       candelabra bulb shape G Globe bulb or circular bulb

    • (HK) Hexagonal Candle

    • (K) Krypton or narrow reflector light bulb shape MB

       Halogen bulb

    • (MR) Quartz reflector lamp (low wattage)

    • (P) Pear bulb shape

    • (PAR) Parabolic Aluminized Reflector (PAR) lamp PS

       Elongated standard incandescent bulb

    • (R) Reflector light bulb style

    • (S) Strait Sided bulb style

    • (T) Tube lamp shape





A Shaped Light Bulbs

“A” type bulb shapes are standard house hold light bulbs. The number after the bulb shape is the number of eighths of an inch in diameter. For metric measured bulbs the number following the bulb shape is the number of millimeters at the widest point of the bulb. Standard bulb sizes include A19 for imperial measurements and A60 for a slightly smaller metric measured bulb.




Bulb Shape CC Shaped Light Bulbs

C shaped bulbs are also known as Candelabra Light Bulbs. They have a bulged base that tapers to a rounded or pointed tip. In some bulbs the tip is bent giving the slight look of a flicking flame.


These bulbs are common in chandeliers, night lights and lower wattage applications such as holiday string lights. Typical bases for C shaped bulbs are E14.



Bulb Shape PARPAR Light Bulbs: PAR16, PAR20, PAR30 and PAR38

PAR lamps stand for parabolic aluminized reflector lamp which has reflective surface to focus the light. For LED lamps the PAR description is used to define the shape, as most do not have a reflective surface due to the directional nature of LED lamps.


PAR ShapesCommon PAR lamps include the PAR20, PAR30 and PAR38, though many other sizes exist. These can give various beam angles that can make good spot and flood lamps.


This shape is very similar to the R shape and in some cases the PAR and R are interchangeable as shapes for LED replacements.




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