A finance team asking for a one-page payback calculation on a mercury-to-LED conversion rarely wants a lecture on photoinitiator chemistry — they want a number, built from the facility’s own shift length, cycle time, and electricity rate, that they can defend in a capital budget meeting.

Step 1: Log the Existing Mercury System’s Actual Draw

Start with a clamp meter on the existing mercury lamp’s power supply, not the nameplate rating — power supplies, cooling fans, and shutter actuators all draw continuously whenever the system is powered on, and the nameplate lamp wattage alone understates total system draw. Record this reading over a full shift, including idle periods between parts, since mercury systems typically cannot be powered down between cure cycles without triggering a multi-minute warm-up delay before the next part can be processed.

Step 2: Establish the Real Cure Duty Cycle

Divide actual light-on cure time by total cycle time for a representative part. A line running a 4-second cure step inside a 25-second total cycle has a 16% duty cycle — meaning the mercury lamp burns at full rated power for the other 84% of every cycle with no useful curing happening during that interval. This number matters more than any single efficiency percentage on a spec sheet, because it’s the multiplier that determines how much of the mercury system’s total energy draw is genuinely wasted versus productive.

Step 3: Estimate Comparable UV LED Draw for the Same Cure Requirement

A UV LED system sized to match the mercury lamp’s delivered irradiance at the working distance in question typically draws a fraction of the mercury system’s steady-state wattage, and — because LEDs switch on and off in milliseconds without degradation — draws essentially nothing during the non-curing portion of the cycle. For worksheet purposes, use the LED supplier’s rated active-curing wattage and treat idle draw as negligible; a standby draw under 5 W is typical for most LED controllers and immaterial next to a mercury system’s continuous multi-hundred-watt draw.

Step 4: Build the Per-Shift Energy Comparison

Multiply each system’s average draw by shift length in hours to get kilowatt-hours per shift. As a worked illustration: a facility running an 8-hour shift with a mercury system averaging 900 W continuously consumes 7.2 kWh per shift regardless of how many parts actually pass through the cure zone. A UV LED system replacing it, drawing 150 W only during the 16% of cycle time that’s actually curing, consumes roughly 1.15 kWh across the same shift for equivalent throughput — the exact ratio will vary by installation, but the calculation method is the same regardless of the specific numbers involved.

Step 5: Convert Energy Savings to a Dollar Figure

Multiply the per-shift kilowatt-hour difference by the facility’s actual electricity rate (not a national average) and by shifts per year to get an annual energy savings figure. This is the number finance teams actually want, and it’s straightforward once steps 1 through 4 are filled in with real, measured data rather than vendor-supplied averages.

Step 6: Add Non-Energy Cost Avoidance to the Same Worksheet

Energy is rarely the only line item in a realistic payback calculation. Mercury lamp replacement cost, hazardous-material disposal fees for spent mercury bulbs, and the labor and downtime associated with each replacement cycle all belong in the same worksheet, since mercury lamps typically require replacement on a schedule measured in months under continuous industrial use, while UV LED arrays are rated for years of service under comparable duty. Reduced unplanned downtime from lamp failure is harder to quantify precisely but should at minimum be noted as a qualitative factor alongside the harder numbers.

Step 7: Divide Capital Cost by Total Annual Savings

Once annual energy savings, avoided replacement cost, and avoided disposal cost are summed, divide the UV LED system’s installed capital cost by that total to get a payback period in years. Facilities running high duty-cycle, high-volume lines typically see the shortest payback windows, since the energy-waste multiplier from Step 2 scales directly with production volume; lower-volume or intermittent operations should expect a longer payback period and may want to weight the maintenance and disposal savings more heavily in the decision, since those accrue somewhat independently of throughput.

Using the Worksheet for a Multi-Station Facility

For a facility with several cure stations running different cycle times, complete Steps 1 through 4 separately for each station type rather than applying one facility-wide average — a manual bench station with a 20% duty cycle and a high-speed conveyor line with a 60% duty cycle will show meaningfully different payback economics, and averaging them together can make a strong business case on the conveyor line look weaker than it actually is, or vice versa for the bench station. For background on the underlying reasons mercury systems are being phased out beyond energy cost alone, why UV LED lamps are replacing mercury vapor systems covers the regulatory and maintenance drivers in more depth, and Incure’s L-Series™ UV LED flood lamp selection guide is a useful reference once a station’s duty cycle and required cure area are known.

If you’d like help filling in this worksheet with your own facility’s measured data rather than illustrative figures, Email Us and an Incure applications engineer can walk through the calculation station by station.

A defensible payback number comes from measured duty cycle and real electricity rates, not a vendor’s headline efficiency percentage. Contact Our Team to build a station-specific energy and cost comparison for your production line.

Visit www.incurelab.com for more information.