by Catherine Green†, All Printing Resources
Why should I replace my bulbs if they still illuminate?
UV-A and UV-C exposure bulbs lose output intensity over time. The gases inside the bulb become inert, resulting in longer start up time while the UV output diminishes. This results in longer, inconsistent exposure times.
If you have an integrator on your exposure unit you may not be aware of the change because the integrator compensates for the difference. We suggest a weekly test of the number of seconds that correspond to the number of units for your standard exposure. This will enable you to determine how much strength your bulbs have lost. If you do not have an integrator, we suggest doing a weekly exposure test using your own test image or one supplied by your plate supplier. This image should contain all of the standard elements needed to properly evaluate the plate. These include, various screen tints, isolated dots, lines, type, solids and reverses. By using the same exposure time each time and saving the last test plate for comparison you will be able to see any noticeable change in your exposure times. The most efficient method to test your bulbs is to use a UV-A meter. This unit reads the bulb intensity and produces a numerical reading. You can record the readings and determine when your bulbs need to be replaced. It is widely recommended to replace your bulbs once they reach 10mW/cm2 or below, although this number can be higher for high-LPI work and HD Flexo.
A note about exposing HD Flexo plates:
Esko recommends UV-A output no lower than 18 mW/cm2 for all HD Flexo plate exposures. We have found that this guideline can vary depending on the photopolymer used. The APR Technical Solutions Group can assist you with specific questions (Contact us).
When you first turn on the power to your equipment (cold start), it provides high voltage until the bulbs light. This strains the starting circuitry, power supply and the quartz (glass) of the bulbs. If you allow excessive start time to the cold start and exposures with old lamps you risk equipment failure.
Unreliable and inconsistent bulbs can cause re-makes and wasted material. We suggest bulbs be replaced before they burn out. Save a few of your old ones as temporary replacements. When replacing bulbs, replace all of them at the same time. This will give you quicker exposure times and your equipment will operate at maximum efficiency.
How can I get the maximum usage from my bulbs?
Here are a few simple steps to get the most from your investment in new bulbs:
- Use cotton gloves when installing new bulbs. If you clean them before use and install them using gloves you will avoid the oils from your fingers and other contaminants that can cause premature failure due to the high operating temperature in your exposing equipment.
- Clean your bulbs on a regular basis to ensure the maximum reflected light.
- Check the electrical contacts regularly for pitting or corrosion, which can cause arcing and failure of the bulb or equipment.
- When installing new bulbs, apply pressure at the ceramic or metal ends never apply pressure to the quartz.
- If your exposure unit has cooling fans and or filters, clean the blades, lubricate the motor bearings as needed, and check to make sure the fans are operating properly. The vents must be clean and free of any obstruction to allow for maximum ventilation and unrestricted airflow. Keeping your bulbs cool will improve their life.
- Make sure that the bulbs you are using are the correct type for your equipment. Many units require specific spectral output. If you change types, make sure your equipment is compatible.
- When you install new bulbs, record the date, life hours and bulb part number. This simple record will help you establish an effective maintenance and replacement schedule.
And lastly, don’t be intimidated by equipment manufacturers who insist you use only their brand of bulb. The bulb simply receives the output from the power supply, so it cannot harm your equipment. Just be certain to buy from a reliable supplier that will make sure you have the correct bulb for your equipment, and be able to help you should a problem arise.
As LED exposure technologies become more popular, it is important to note the difference between these technologies and bank light systems. LED systems have variable output, so the light intensity can be easily controlled and adjusted. Also, LEDs are temperature-controlled and instantly light to full power, so there is almost no variation in the exposure process. APR represents both Esko’s Inline UV exposure solutions, as well as Flint Group’s NExT flat-top LED exposure technology.
† Based on an article originally written by Larry Dingman in November of 2002, updated in August of 2014 by Catherine Green.
About the TSG:
We have formed our Technical Solutions Group to encompass our full range of expertise in all critical areas of the flexo process. This team is made up of industry professionals dedicated to being up to date on new technologies, armed with the last in diagnostic tools, and experienced in problem solving that can achieve sustainable results. The TSG have walked in your shoes, and has felt your pain. For any specific questions about determining plate wear through reflectivity readings and 3D color mapping or assistance in determining your plate wear pass/fail limits, please feel free to contact us.