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Linear Fluorescent Light Bulbs

Fluorescent Linear (Tube) Light Bulb Things to Know

What size fluorescent bulb do I have?
Linear fluorescent light bulbs are measured in two ways length and diameter.  The length is measured from the end the pins. The most common sizes in length for T12's and T8's are 12, 15, 18, 24, 36 and 48 inches long.  Howerver, T5 light bulbs are metric and standard sizes are not the same as T12 and T8.  Some of their common sizes are around 22, 34 and 46 inches.  The second measurement is the diameter of the light bulb. Fluorescent tube light bulbs are measured in 1/8 of inch increments.  So a T12 light bulb is 12 x 1/8 of an inch, which equals 1 1/2 inches in diameter (T8 equals an inch and T5 equals 5/8 of an inch)

What wattage do I need?
The size of the light bulb will narrow the options of wattages that are available in your application.  The first place to look is on the end of the bulb you are replacing.  It should have the wattage of the bulb printed on it.  If it is not there then take a look around the fixture it was removed from and look for some markings that tell you what fluorescent light bulb to use.  Fluorescent linear light bulbs do come in some energy saving options.  So you may have a standard F32 T8 light but there may be not only the 32 watt option but also a 25 and a 28 watt energy saving version.   In most cases you do not need to change anything in the fixture to use these lower wattage energy saving options.

What is color temperature?
You may notice that many of the linear fluorescent light bulbs are the same size and wattage but a different color temperature.  Color temperature is what tells you what color the light is that the bulb produces and it is measured in kelvins (K).   Kelvin temperature for fluorescent light bulbs ranges from 2700 kelvin to 6500 kelvin.  2700 kelvin is a similar color to incandescent light bulbs and is referred to as warm white (yellow white color).  As the number gets bigger the light becomes cooler and at 6500 kelvin it is referred to as cool daylight (blue white color).  Below are the basic levels of color temperature available and a short definition.

  • 2700K - Warm White (incandescent light)
  • 3000K - White (halogen light)
  • 3500K - Cool White 
  • 4100K - Cool White
  • 5000K - Daylight (noon sunlight)
  • 6500K - Cool Daylight (overcast sunlight)

What is Color Rendering Index (CRI)?
Color Rendering Index (CRI) at its basic level is how well the light that the bulb is producing renders color.  Incandescent and halogen light bulbs have a rating of 100 (which is the highest level).  They produce true and vivid colors.  Fluorescent linear lights can have rating as low as 65 and as high as 90.  If having true colors that do not look washed out is important to you, I would make sure you get a bulb that has a CRI of 80 or higher.

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