AGL Lamp Life at Circuit Current Calculator
Fits a power law to two lamp life readings from a data sheet and gives the life at another circuit current, with the replacements a circuit needs each year.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
Open in the calculator with these values
About this calculator
This page calculates life exponent m, life at the evaluated current, life relative to the first point and 1 more result from first data point current, first data point life, second data point current, second data point life and 3 more inputs. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
Two points fix the curve exactly, so the answer is only as good as the readings. Staying between the two points is safer than going beyond them. Use the manufacturer curve where one exists.
Cross-check: 25 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Indicative
Indicative. Estimation only; further engineering checks are required. Basis: Empirical life-versus-current relationship; manufacturer curve governs.
What this calculator checks
- The arithmetic of the simplified model for the values you entered.
What remains unverified
- Whether the simplifying assumptions listed on this page hold for your case.
- Any standard, manufacturer or site data. Treat the result as an estimate and confirm it by a further engineering check.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | Not applicable: Lamp life versus current is empirical and fitting-specific. The calculator interpolates manufacturer-provided life points; no universal AGL standard prescribes its exponent. |
| Standard review state | Not applicable |
| Scope-screening note | not recorded |
| Cross-check test cases | 25 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Indicative |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| First data point: current | 6.6 A |
| First data point: life | 1,000 h |
| Second data point: current | 6.1 A |
| Second data point: life | 2,000 h |
| Current to evaluate | 5.2 A |
| Fittings on the circuit | 60 |
| Hours of operation per year | 4,380 |
- m = ln(2,000 / 1,000) / ln(6.6 / 6.1) = 8.798
- Life = 1,000 h × (5.2 / 6.6)^(−8.798) = 8,147 h
- Replacements = 60 × 4,380 / 8,147 = 32.3 a year
Assumptions
- Life follows a power law in the circuit current between the points
- Rated life is an average, so some lamps fail earlier
- Operating hours are all at the evaluated current
Two points fix the curve exactly, so the answer is only as good as the readings. Staying between the two points is safer than going beyond them. Use the manufacturer curve where one exists.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| First data point: current | A | greater than 0 A | From the lamp life curve or data sheet |
| First data point: life | h | greater than 0 h | |
| Second data point: current | A | greater than 0 A | A different current from the first |
| Second data point: life | h | greater than 0 h | Example values only. Use the readings for your lamp. |
| Current to evaluate | A | greater than 0 A | |
| Fittings on the circuit | (number) | 1 or more, up to 500 | |
| Hours of operation per year | (number) | greater than 0, up to 8,760 | At the current to evaluate |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Life exponent m | (number) | Shown to 2 decimal places | |
| Life at the evaluated current | h | Shown to 0 decimal places | |
| Life relative to the first point | (number) | Shown to 2 decimal places | |
| Lamp replacements per year | (number) | Shown to 1 decimal place |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with first data point: current
| First data point: current (A) | Life exponent m | Life at the evaluated current (h) | Life relative to the first point |
|---|---|---|---|
| 0.66 | -0.31 | 1,903 | 1.9 |
| 1.65 | -0.53 | 1,838 | 1.84 |
| 3.3 | -1.13 | 1,670 | 1.67 |
| 6.6 | 8.8 | 8,147 | 8.15 |
| 13.2 | 0.9 | 2,308 | 2.31 |
| 26.4 | 0.47 | 2,157 | 2.16 |
| 66 | 0.29 | 2,095 | 2.1 |
Other inputs are the same as in the worked example above.
Standards and further reading
- ICAO Annex 14, Volume I (aerodrome design and operations)
- ICAO Doc 9157, Part 5 (aerodrome design manual, electrical systems)
Photometric and circuit requirements come from the edition of Annex 14 and the regulator's rules that apply at your aerodrome, and from the fitting and regulator manufacturers' data. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter first data point: current, first data point: life, second data point: current, second data point: life, current to evaluate, fittings on the circuit and hours of operation per year. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Life follows a power law in the circuit current between the points. Rated life is an average, so some lamps fail earlier. Operating hours are all at the evaluated current.
Which calculators should I use next?
Common next steps are AGL Brightness Step Current and Circuit Load and AGL Maximum Fittings on a CCR. The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 25 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- AGL Lamp Life Formulas: AGL lamp life formulas: a power law fitted to two lamp life readings
- AGL Brightness Step Formulas: AGL brightness step formulas: the circuit current at each step of a 6.6 A series circuit, and the lamp load
More Airport and AGL Engineering calculatorsAll engineering calculatorsAGL Lamp Life at a Different Circuit Current in Elecmetric