Fluorescent Lamps and Inverters, Including UV Lamps


Question: What type/size wire is needed for fluorescent lamps?

Answer: The wire must have insulation at or above 1500 volts. Small gauge 26 or 28 is acceptable. See JKL application note AI-004 for details.

Question: How do I drive a cold cathode fluorescent lamp?

Answer: Miniature fluorescent lamps operate on AC. They are low pressure discharge lamps which are filled with a noble gas (typically argon) and a small amount of mercury in a phosphor-coated tube. They are also vibration and shock resistant, offer variable levels of brightness and consume very little power.

Question: How far can I position a lamp from its inverter?

Answer: This is dependent on the combination of lamp and inverter and their proximity to the ground plane. As a rule, the maximum lead length should be eight inches or less. If lead lengths are unequal, the ground lead should be the longer. Using the proper type wire and insulation is important. See Application Note.

Question: Can I be shocked by the inverter or the fluorescent lamp?

Answer: Yes! Although current is low, the inverter output can exceed 1000 volts. Proper precautions should be observed when operating these lamps and lamp assemblies.


Question: Does the fluorescent lamp and inverter produce EMI or RFI?

Answer: They combine to produce some RFI emission and it may be necessary to shield the inverter after determining results of system testing. The wipe, the interconnections and the high frequency inverter are all sources of potential EMI.

Question: How much mercury is contained in fluorescent lamps?

Answer: This varies by lamp diameter, typically 3mg for 3.2mm diameter to 9mg for the 9mg diameters. Always use care in disposing of failed lamps at a proper recycling facility. See JKL application note for details.

Question: How much infrared is present in JKL ultraviolet lamps?

Answer: Less than 5% of peak output is present, and is primarily at lamp ends.

Question: Are lamps and inverters approved to UL, CSA, TUV, VDE or other safety standards?

Answer: Safety agency approvals have not been sought for these components, because most companies obtain agency approval at the system level. The PC Board does not have an UL listing. Individual components in the inverter have UL approvals.

Question: Will fluorescent lamps work at cold ambient temperatures?

Answer: The lower the temperature, the lower the light output and the higher the required starting voltages. See Chart on CCFL Start-Up at 5mA. Lamps can be supplied with heaters.


Question: Do fluorescent lamps get hot?

Answer: When operated at the specified drive current of 5mArms, the lamp ends near the electrodes will be approximately 40°C above ambient. The glass body will be 10° to 15° C over ambient.


Question: What is the shelf life of fluorescent lamps?

Answer: Typically, the lamp shelf life is over ten years.

Question: How long should I expect fluorescent lamps to last?

Answer: Typically 20,000 to 50,000 hours when operated within specification parameters. Lamp life is defined as the point at which the lamps emitted brightness and uniformity is reduced to 50% of its initial output.


Question: What is the effect of lamp length or diameter on brightness?

Answer: Using the same drive current, the surface intensity of a smaller diameter lamp will be greater. Longer lamp lengths of the same diameter have greater total light output.

Question: How much of the lamp's overall length is actually lit?

Answer: The entire length gives off illumination, except for 5 to 8mm at each end.

Question: Can fluorescent lamps be flashed on and off?

Answer: Yes. The turn-on time can be controlled, but the turn-off time is limited to the specific decay properties of the phosphor, which varies.

Question: How can I increase lamp brightness?

Answer: Lamp brightness may be elevated by increasing the drive current. This is not recommended because it will shorten lamp life and may shift the output spectrum. See Application Note.


Question: What are the preferred methods of mounting fluorescent lamps?

Answer: Any method that does not put stress on the glass envelopes and/or the lead to the glass seal on the lamp end is acceptable. Most common methods are to solder the leads (with a strain relief bend) directly into a PC board, or to secure the lamp ends with a custom silicone end cap for greater shock/vibration isolation.


Question: Can I power fluorescent lamps directly from the wall outlet?

Answer: No! You must use a properly matched inverter. All lamp specifications and operating characteristics are based on inverter power.

Question: Can I run more than two lamps on a single inverter?

Answer: It is possible to run more than one lamp, either in series or parallel operation. For optimum performance and recommendations, consult a JKL lighting specialist about the specific lamp/inverter combination you are seeking.


Question: Are special or custom fluorescent lamps (i.e., non-standard colors, diameters or shapes) available?

Answer: Specials may be obtained. However, minimum order quantities and set-up charges would likely be required.

Question: Are there any limits on lamp length for miniature fluorescent Lamps?

Answer: The limit is dependent on the diameter of the lamp and the availability of an inverter to properly drive the lamp. 3mm lamps would typically be from 25mm to 440mm long, while 8mm lamps are 1000 to 1000mm in length.

Incandescent Miniature Lamps


Question: How do I determine the Wattage of a lamp?

Answer: To obtain the wattage of any given lamp, multiply the voltage and amperage (for example: 28 volts x .040 Amps = 1.12 watts).

Question: How do I calculate a lamp's inrush current?

Answer: To determine inrush current, multiply the stated current value by 10. The duration of the inrush current on most lamps is 30 to 40 milliseconds. For example: 0.040 amps x 10 + 0.40 amps.

Question: How do I determine the current draw on a lamp?

Answer: 1.12 watt divided by 28 volts = 0.040 amps).


Question: What is the importance of Operating Current on Lamp Life?

Answer: Most performance specifications listed in manufacturer's catalogs are based on lamps operating on AC Input Voltage. Because a large number of applications utilize lamps with DC solid-state circuitry, these specs become meaningless. Caution: System operation on DC reduces lamp life by nearly 50%!


Question: What is the most common cause of incandescent lamp failure?

Answer: It most often occurs due to a mechanical break in the filament winding and may be accelerated by the amount of stress to which the lamp is subjected. A lamp operating at an elevated ambient temperature or at increased voltage will fail much faster than one used a rated voltage. Selection of a correct filament increases useful life.

Question: Why is the filament such an important component of the lamp?

Answer: During start-up, inrush current through the filament is up to 12 times normal rating and lasts for 20 to 40msec. Current surge can cause premature failures towards end of lamp life. This can be avoided by using varistors and diodes to slowly ramp current. Nonetheless, a tungsten filament is more brittle at room temperature than at high temperature.

Question: What are the benefits of using noble gasses (xenon, krypton, argon) for increased life, and how does their use affect cost?

Answer: Halogen extends operating life by recycling tungsten, evaporated from the filament and deposited on the inside of the glass lamp, back on to filament coil. It keeps the lamp from turning gray/black and allows brightness to remain at or near initial brightness specs for up to five times that of standard incandescent lamps. Lamps using an inert gas such as argon physically suppress evaporation of tungsten from the filament. The heavier the atomic weight of the gas used, the greater its effectiveness. This also increases the cost of the lamp, but provides the added benefit of NO reduced life operating on DC voltage, and a whiter, more efficient light that is very desirable where color is a serious consideration.

Question: How can I Increase lamp life without increasing cost?

Answer: The most basic way is to reduce or derate input power. In many applications, there is little if any need for a lamp to operate at its maximum rated voltage. An incandescent lamp operating at 80% of its rated power requirement will still deliver 50% of its brightness, while increasing lamp life by 350%!. CAUTION: This does not work with halogen lamps. IF you reduce operating voltage below stated performance ratings, you will reduce the benefit of life, brightness, white light, etc. achieved by the halogen cycle.

Question: What is the real definition of lamp life, and what makes it important to me?

Answer: This is one specification you cannot afford to misunderstand. Rated lamp life is computed on the point at which 50% of all lamps in a lot have failed. So, if your rated lamp life is 10,000 hours, ONE HALF of all the lamps may have failed at that point. Now if you're basing your "free replacement" policy for failed lamps on the 10,000 hours rated life, you'll be absorbing the cost on AT LEAST 50% of all the lamps installed in your products. PLEASE don't let sometimes misleading specifications lead you into a sense of false security. An appropriate formula for first failure is 35% of rated lamp life.products. PLEASE don't let sometimes misleading specifications lead you into a sense of false security. An appropriate formula for first failure is 35% of rated lamp life

Question: Are performance specifications a real guide to lamp life?

Answer: All lamp performance specifications are based on ideal, vibration-free conditions with stable room temperature. The presence of shock and vibration, or designs that physically encapsulate the lamps in a cavity and elevate ambient temperature, will significantly affect lamp life and reliability.

Question: What is the effect of voltage change on incandescent lamp life?

Answer: Incandescent lamp life is significantly affected by voltage, shock and vibration. Raising voltage by only 5% above a lamp's design level can reduce life by 50%. As a result, life and/or light output curves only provide reasonably accurate performance levels between 95% and 105% of rated voltage, and then only when operated in a totally controlled environment.

Question: How does lamp vacuum affect lamp life?

Answer: The degree of vacuum achieved during the lamp sealing process has a pronounced affect on lamp life. While seldom addressed as part of a lamp specification, the greater the vacuum, the longer and more stable the lamp life. If oxygen is left within the lamp envelope due to an inferior vacuum process, it will react with the filament and produce early failures.


Question: I understand that the higher the wattage, the brighter the lamp. Is that true?

Answer: Miniature lamps follow no such convention. Three lamps with identical voltage, current and wattage specifications may have an MSCP rating ranging from 0.3 to .15, and a rated life from as much as 200,000 hours to as little as 5,000 hours. These variations are governed by factors such as filament length, diameter, and coil spacing employed to achieve desired photometric characteristics.


Question: What is filament notching?

Answer: DC notching is a phenomenon that occurs to an incandescent lamp when operated on DC voltage. The Tungsten material flows in the direction of the current and stops when it has reached its elasticity point and then starts to flow again. This movement creates various weak points within the filament wire, shortening the average rated life by approximately 50%.

Light Emitting Diodes (LED)


Question: What is the typical operating voltage of an LED?

Answer: The typical voltage for most LED's is from 1.8V to 2.2V. A blue LED has a slightly different range from 3.0V to 3.5V. Various LED are produced with an internal resistor for 5.0V, 12.0V and 24.0V operation.

Question: Is an LED a polarized device, and if so, how can I tell the Anode (positive) connection from the cathode (negative) connection?

Answer: Yes. An LED needs to be operated in a polarized DC circuit. Typically, the cathode of an LED is indicated by a short lead or flat on the flange.


Question: What is the effect of temperature on LED operation?

Answer: A modest increase in ambient temperature will dramatically inhibit light output of an operating LED device. While most devices are rated at 25oC (ambient room temperature), operation at a higher temperature (85oC) could cause light intensity to drop to 40-60% of rated value.


Question: How long should I expect an LED to last?

Answer: Today, the averagered, green and amber LED device has a half-life of over 20 years continuous use, and offer an appealing alternative to incandescent lamps in a variety of operations. LEDs with blue spectral output, and white LEDs using a phosphor coating, have a greatly reduced lifetime. Check the specification for up-to-date parameters.


Question: What determines the emitted color of an LED?

Answer: There are a variety of different semiconductor die materials and combinations of materials that are used to create the emitted color an LED produces. Each material has a certain characteristic for a specific visible spectrum of color. Colorants are often added to epoxy to filter and facilitate sorting of the LED.

Question: What is the peak wavelength of an LED, and how is it measured?

Answer: LEDs emit light in a narrow band of wavelengths, perhaps 30 nanometers wide. The single wavelength that is most intense (or brightest) in the center of this narrow band is known as the "peak" wavelength. The band gap or energy level of the semiconductor materials used to produce the LED determines its peak wavelength.

Question: Do LED lens types affect brightness?

Answer: Definitely. Although they carry many different designations throughout the industry, specifiers would be wise to list them in four generic categories, listed in descending order from most to least light transmissiveness, and likewise in the LED Level of Efficiency:

  • Water Clear
  • Tinted-Transparent
  • Tinted Diffused
  • Milk White-Diffused

Question: Are there any developments to improve or more clearly identify brightness?

Answer: With the utilization of water clear GaAlAs, greater efficiencies have been achieved in LED brightness. It's important to remember that the highest brightness levels are typical only of red LEDs. For comparison, a very bright red LED has from 3000 to 5000 mcd brightness, while a green LED with a comparable brightness will only have from 600 to 800 mcd. Brightness levels for "standard" LEDs throughout the industry are only 1 to 5 mcd at 20mA.

Question: Why is there so much confusion about LED brightness levels?

Answer: There are no industry standards for brightness. This causes significant problems for users. One company may call an LED with a brightness of only 20mcd at 20mA an "Ultra-Brite" while another might offer the same designation to a device with 200mcd at 20mA. You must evaluate the specs and ignore descriptions like "Ultra", "Super" or "Blinding"?. White and blue LEDs have a significantly lower life rating, approximately 10 percent that of red output LEDs.

Question: What devices are used to measure wavelengths in an LED?

Answer: A spectroradiometer separates light into wavelengths and measures the intensity of each wavelength. The device, which splits the light into individual wavelengths, is a series of closely spaced parallel grooves on glass. The distance between the parallel grooves determines what wavelength will pass through. For a given spacing, only one wavelength will pass through. Shorter and longer wavelengths are blocked. After the wavelength passes through the grating, a light sensor (which may be a photo multiplier tube or a solid-state sensor such as a silicon photodiode) measures the intensity.


Question: Are there many different types of LED devices?

Answer: There are many discrete (leaded) and multi-chip (based) LED devices. Generally speaking, they offer a narrow viewing angle and their brightness is temperature dependent for light output. Specify size, surface mount or radial leads, color requirements and brightness.