Previous against current test for each fixture: percent degradation, rate per year, time to the limit and a maintenance priority.
Paste the previous and current intensity for each fixture and enter the two test dates. The tool works out how much each fixture has lost, how fast, and, if you enter a required minimum, how long it has before it falls below it. It then ranks the fixtures into critical, high, medium and low priority using thresholds you set. It holds no standard values and projects in a straight line only, so treat the time-to-limit as a planning guide, not a prediction.
Needed for the yearly rate and the time to the limit. Without both dates, only the degradation between the two tests is shown.
Take the specified main-beam average intensity for your light type and apply the serviceability level your authority uses. ICAO Annex 14 treats a light as unserviceable below 50 % of the specified value, and FAA guidance treats an in-pavement light below 70 % of the minimum output as ineffective. Confirm the figure in the current edition. The default is an example only, not a standard value.
A fixture already below the required minimum is always Critical. All thresholds are placeholders for your own maintenance procedure. The month limits apply only when a required minimum and both dates are entered.
One fixture per line, separated by comma, tab or semicolon. Two numbers on a line are taken as previous and current, with the fixture numbered automatically. Do not use thousands commas. A header line is skipped.
| Fixture | Previous | Current | Change | Degradation | Per year | % of required | Months to limit | Priority |
|---|
Every step is shown so the result can be checked by hand.
The loss between the two tests as a percent of the previous reading. A negative value means the fixture read higher this time.
The interval between the test dates is converted to years (days ÷ 365.25). The yearly rate is the degradation divided by that interval, and the yearly loss in intensity is the drop divided by the interval.
If the required minimum is entered, the fixture's yearly loss is projected in a straight line from its current reading down to that minimum. A fixture with no loss never reaches it on this projection.
Critical when the current reading is below the required minimum. Otherwise High if degradation reaches your high level or the limit is within your high months, Medium on the medium levels, and Low for the rest. The degradation tested is either the total change or the annualised rate, as you choose.
Example values only, not a standard.
| Item | Value |
|---|---|
| Tests | 10 Oct 2025 and 10 Oct 2026 (1.00 yr) |
| Fixture EL-03 | 11,900 → 9,400 cd |
| Degradation | 21.0 % |
| Yearly loss | 2,500 cd per year |
| Required minimum | 10,000 cd |
| Result | Below required now, Critical |
It does not hold standard values, correct for supply current or temperature, or fit a curve to more than two tests. The projection is linear and uses only the last interval. Lamps often degrade unevenly, so use the months figure to plan inspections, not to schedule a replacement date.
Quick answers on comparing a previous and a current photometric test for each fixture.
It compares a previous and a current intensity test for each fixture and works out the percent degradation, the rate per year, the time to a required minimum and a maintenance priority. It then ranks the fixtures into critical, high, medium and low priority using thresholds you set. It holds no standard values.
Degradation is the loss between the two tests as a percent of the previous reading, which is previous minus current, divided by previous, times 100. A negative value means the fixture read higher this time.
The interval between the two test dates is converted to years by dividing days by 365.25. The yearly rate is the degradation divided by that interval, and the yearly loss in intensity is the drop divided by the interval. Without both dates, only the degradation between the two tests is shown.
If you enter a required minimum, the fixture's yearly loss is projected in a straight line from its current reading down to that minimum. The months to the limit are the current reading minus the required minimum, divided by the yearly loss, times 12. A fixture with no loss never reaches the limit on this projection. Lamps often degrade unevenly, so use the figure to plan inspections and not to schedule a replacement date.
A fixture is Critical when its current reading is below the required minimum. Otherwise it is High if its degradation reaches your high level or its limit is within your high months, Medium on the medium levels, and Low for the rest. The degradation tested is either the total change or the annualised rate, as you choose. All thresholds are placeholders for your own maintenance procedure.
Paste one fixture per line as ID, previous, current, separated by a comma, tab or semicolon. If a line has two numbers they are taken as previous and current, and the fixture is numbered automatically. Do not use thousands commas. A header line is skipped, and you can also load a CSV file. The ranked list can be downloaded as a CSV file.
With tests on 10 Oct 2025 and 10 Oct 2026, which is 1.00 year, fixture EL-03 goes from 11,900 cd to 9,400 cd. That is a degradation of 21.0 percent and a yearly loss of 2,500 cd per year. Against an example required minimum of 10,000 cd it is below the required level now, so it is Critical. These are example values only, not a standard.
It does not hold standard values, correct for supply current or temperature, or fit a curve to more than two tests. The projection is linear and uses only the last interval. Differences between two tests include instrument, distance, aiming and lens-cleaning effects as well as real lamp ageing, so confirm large changes with a repeat reading before acting. The required minimum and thresholds shall come from the applicable standard and your maintenance procedure.
Enter the minimum main-beam average intensity for your light type from the applicable standard, multiplied by the serviceability level your authority applies. ICAO Annex 14 treats a light as unserviceable when its main-beam average intensity is below 50 percent of the specified value. FAA guidance treats an in-pavement light below 70 percent of the minimum required output as ineffective. Confirm the figure in the current edition. The tool holds no standard values, and the default shown is an example only.
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