“CFL” is a household name at this point. Developed in 1985, the compact fluorescent light bulb is now a 25-year-old product present in 70 percent of homes in the United States. Just last year, more than 273 million CFLs were sold in the U.S.
Cold cathode fluorescent light bulbs are a little less familiar, at least to the general public. Here’s a quick overview of the core differences.
All fluorescent light bulbs have two cathodes (one at each end). In a standard CFL, the cathodes are made of coiled tungsten filaments that are heated to approximately 900 degrees Fahrenheit each time the light bulb is turned on. That heat releases electrons. The electrons shoot back and forth between the cathodes and react with the mercury to create ultraviolet radiation, which in turn reacts with the phosphor coating on the inside of the glass envelope to create light. Standard CFLs are hot cathode light bulbs.
In a cold cathode fluorescent light bulb, the cathodes are made of a solid metal thimble, which is more durable than the thin coils in standard CFLs. The cathodes only heat up to about 200 degrees Fahrenheit (certainly not “cold”, but relatively cooler than the hot cathode filament, hence the name). The voltage potential within the tube excites the mercury to cause current flow.
- CFLs have limited dimming capabilities.
- CCFLs are dimmable down to 5% of light output, making them similar to incandescent light bulbs.
Reducing the voltage to a hot cathode fluorescent ballast in turn reduces the temperature of the cathodes. CFLs require cathodes to be hot enough to emit electrons in order to excite the mercury atoms.
The cathodes on CCFLs do not need to be heated as much to operate (see technological differences). Also, the solid metal thimble in a CCFL can withstand dimming better than the thin coil filament in a CFL.
- CFLs, when used in flashing signs, experience a significant decrease in average rated life.
- CCFLs are ideal for flashing signs.
The solid metal thimble inside a cold cathode fluorescent light bulb can withstand shock and vibration better than the tungsten filament inside a hot cathode fluorescent light bulb.
- Up to 15,000 hours in a CFL
- Up to 25,000 hours in a CCFL
CCFLs have a longer average lifetime from the start, equivalent with some LEDs. In addition, due to more durable cathodes, CCFLs are rarely affected by different modes of operation, such as rapid on-off cycles. The lifetime of a CFL, in contrast, is significantly shortened (up to 85%) if it is consistently only turned on for a few minutes at a time.
- When CFLs are first switched on, they typically only provide 50-80% of their potential light output, and may take up to three minutes to achieve full brightness.
- CCFLs turn on instantly to full light output.
Because the cathodes in CFLs must heat up to 900 degrees, there is a lag in start time, which is exacerbated by cold weather.