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contact usThere are hundreds of types of light bulbs on the market. It can be confusing to know which one will be right for your fixture. The shape, end type, and diameter may all be used to determine if a certain bulb will fit. For fluorescents, you need to consider the CRI, Color, and Lumens to help choose the bulb that fits your needs. Here are some helpful hints to help you choose the right bulb. For more information call 800-628-2199.

CRI - This is the Color Rendering Index. It refers specifically to how the color of an object appears under the artificial light source as compared to sunlight. The "cool white" light has a CRI of 62. The IntegraLight Full Spectrum lights have a CRI of 90. Sunlight has a CRI of 100. The higher the CRI of an artificial light, the more vibrant and true-to-life the color of an object will be. This higher CRI not only produces true to life colors, it helps to improve see-ability and makes it easier to perform visual tasks. The full spectrum lights have also been proven to reduce symptoms of Artificial Light Syndrome. These are important facts for museums, galleries, jewelry stores, medical examination areas, printing companies, offices, etc.

Color Temperature - This refers to the quality of light emanating from a light source and is represented by the number of degrees Kelvin based on the Kelvin Color Temperature Scale. Outside light varies from 5500K to 6800K, depending on season, time of day, latitude, and weather. The higher the color temperature of a fluorescent lamp, the "bluer" it's appearance, the lower the color temperature, the "redder" it's appearance.

Lumens - This refers to the amount of light emitted from a light source as measured by a light meter. The typical light meter are most sensitive to the yellow-green part of the colorband. This is the light that is seen by the cone receptors in the eye and is called the "photopic lumens". However, the rod receptors in the eye also receive light but it is the light rich in the blue portion of the spectrum. This light isn't measured by the typical light meter. The combination of the light received by the rods and cones is called the "seeable lumens". Therefore, the photopic lumens could be misleading when comparing different colors of light. Even though a similar lumen reading is obtained with a full spectrum bulb vs. and cool white bulb, the full spectrum bulb will produce more seeable light. A 40W cool white bulb will have about 2650 photopic lumens and 3579 seeable lumens, whereas a 40W Integralight Plus will have 3900 photopic lumens and 6240 seeable lumens.


  • Measure your existing bulb (tip to tip) to make sure you order the correct length
  • Look at the type of end your bulb has (single pin, double pin, recessed double contact, etc) Diagrams of the various types of fluorescent ends are shown below.
  • Check the wattage of your current bulb - this usually follows the letter "F" (ex: F40 = 40W). If the fluorescent tube is longer than 4 ft. the number following is length in inches (ex: F96= 96 inch). An F40T12 fluorescent is the most common fluorescent currently used in America today (F=Fluorescent, 40= 40 watts, T= Tubular shape, and 12= 12/8" of an inch or 1 1/2 inch in diameter). The F96T12 fluorescent is the second largest source of light in America today (F=Fluorescent, 96= 96 inch length, T= Tubular shape, and 12= 12/8" of an inch or 1 1/2 inch in diameter)
  • Check the type of ballast you have (magnetic or electronic). Most T12 and T10 bulbs use magnetic ballasts. The T8 and T5 bulbs use the electronic ballasts. You can also upgrade your ballast to an industrial grade electronic ballast that can be used on ALL bulbs.


Use the diagrams below to help you find the correct shape, size and base for incandescent bulbs. To determine the size (width) of the bulb, measure the maximum diameter of the bulb in eighths of an inch (1/8"). For example: an A19 bulb is 19-eighths of an inch (2 3/8") in diameter. A BR40 flood light is 40/8ths of an inch (5") in diameter.

The most common base size is the "medium" base. This is the base size of the "standard incandescent".

Incandescent lamp descriptions are easy to read once you know how. The format is standard and goes as follows:


  • 40 G 25 / Med / CL / 120V will be for a 40W Globe shaped bulb, 3 1/8" (25/8ths) wide with a medium base. It is a clear glass lamp designed to be used at 120V.
  • 150 PAR 38 / Med / FL / 130V will be for a 150W PAR shaped bulb, 4.75" (38/8ths) wide with a medium base. It is a flood lamp desinged to be used at 130V.

Basic Bulb Shapes

Lamp Bases


I.W.I. Lighting
14 South Main St., Stanley, ND 58784
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