AGL Brightness Step Current Calculator
Circuit current, lamp load, cable loss, CCR output voltage and load at one brightness step of a 6.6 A series lighting circuit.
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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.
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About this calculator
This page calculates circuit current at this step, current as % of 6.6 A, total circuit load at this step and 3 more results from circuit type, brightness step, fittings on the circuit, lamp power per fitting at 6.6 A and 4 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
The highest step normally sets the CCR size, so use the CCR sizing calculator at 6.6 A for that. Use this one to see the output voltage and load at the lower steps and to check them against the CCR curves. Confirm the step currents against your project specification.
Cross-check: 30 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: Engineering reference
Engineering reference. Formula and method documented and tested against separately coded reference calculations. Not yet Verified: the evidence listed on this page is still needed.
What this calculator checks
- The arithmetic of the published formula for the values you entered, in the units shown.
What remains unverified
- That the inputs suit your application. Take ratings, resistances and constants from the manufacturer data sheet or project specification.
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 | IEC 61820-1-2; IEC 61820-3-2; FAA AC 150/5345-10H, IEC 61820-1-2:2024; IEC 61820-3-2:2023; FAA AC 150/5345-10H |
| Standard review state | Public-scope screened; licensed clause review still pending |
| Scope-screening note | AGL series circuit and CCR requirements are relevant. The lamp power/current relationship is entered as an exponent-based model; actual brightness-step currents, lamp data and CCR output data must come from approved equipment documentation. |
| Cross-check test cases | 30 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Engineering reference |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; licensed clause-by-clause standard review; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| Circuit type | 5-step (2.8, 3.4, 4.1, 5.2, 6.6 A) |
| Brightness step | Step 3 |
| Fittings on the circuit | 60 |
| Lamp power per fitting at 6.6 A | 45 W |
| Isolating transformer efficiency | 0.85 |
| Series cable loop length | 4,000 m |
| Series cable resistance | 3.08 Ω/km |
| Lamp power exponent | 2 |
- Step current = 4.1 A (62.1 % of 6.6 A)
- Lamp load = 60 × 45 W × 0.6212^2 / 0.85 = 1,225.8 W
- Cable loss = 4.1² × 3.08 Ω/km × 4 km = 207.1 W
- Total = 1.433 kW, Vout = 1,433 / 4.1 = 349 V
Assumptions
- Step currents are the usual 6.6 A circuit values: 2.8, 3.4, 4.1, 5.2, 6.6 A (5-step) and 4.8, 5.5, 6.6 A (3-step)
- Lamp power scales as a power of the current, with the exponent you enter
- Transformer efficiency is constant at every step
- Resistive series circuit, power factor near unity
The highest step normally sets the CCR size, so use the CCR sizing calculator at 6.6 A for that. Use this one to see the output voltage and load at the lower steps and to check them against the CCR curves. Confirm the step currents against your project specification.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| Circuit type | (choice) | 5-step (2.8, 3.4, 4.1, 5.2, 6.6 A); 3-step (4.8, 5.5, 6.6 A) | |
| Brightness step | (choice) | Step 1 (lowest); Step 2; Step 3; Step 4; Step 5 (highest) | |
| Fittings on the circuit | (number) | 1 or more, up to 500 | |
| Lamp power per fitting at 6.6 A | W | greater than 0 W | At full current, from the fitting data sheet |
| Isolating transformer efficiency | (number) | greater than 0.5, up to 1 | Taken as constant at every step |
| Series cable loop length | m | greater than 0 m | |
| Series cable resistance | Ω/km | greater than 0 Ω/km | |
| Lamp power exponent | (number) | 1 or more, up to 6 | Lamp power at a step = full-current power × (I / 6.6)^k. 2 treats the lamp as a fixed resistance. A tungsten filament cools at a low step and its resistance falls, so its real power is lower and the exponent is nearer 2.5 to 2.7 (power rises about as the 1.6 power of voltage while current rises as the 0.6 power). Using 2 therefore over-states the load at the low steps, which is the safe side for CCR loading. Use the lamp data sheet where you have it. |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Circuit current at this step | A | Shown to 2 decimal places | |
| Current as % of 6.6 A | (number) | Shown to 1 decimal place | |
| Total circuit load at this step | kW | Shown to 3 decimal places | |
| CCR output voltage at this step | V | Shown to 0 decimal places | |
| Cable loss at this step | W | Shown to 0 decimal places | |
| Load as % of the full-current load | (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 lamp power per fitting at 6.6 a
| Lamp power per fitting at 6.6 A (W) | Circuit current at this step (A) | Current as % of 6.6 A | Total circuit load at this step (kW) |
|---|---|---|---|
| 4.5 | 4.1 | 62.1 | 0.33 |
| 11.3 | 4.1 | 62.1 | 0.515 |
| 22.5 | 4.1 | 62.1 | 0.82 |
| 45 | 4.1 | 62.1 | 1.433 |
| 90 | 4.1 | 62.1 | 2.659 |
| 180 | 4.1 | 62.1 | 5.11 |
| 450 | 4.1 | 62.1 | 12.465 |
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 circuit type, brightness step, fittings on the circuit, lamp power per fitting at 6.6 A, isolating transformer efficiency, series cable loop length, series cable resistance and lamp power exponent. Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Step currents are the usual 6.6 A circuit values: 2.8, 3.4, 4.1, 5.2, 6.6 A (5-step) and 4.8, 5.5, 6.6 A (3-step). Lamp power scales as a power of the current, with the exponent you enter. Transformer efficiency is constant at every step. Resistive series circuit, power factor near unity.
Which calculators should I use next?
Common next steps are AGL Series Circuit Load and CCR Size and AGL CCR Input Power and Annual Energy. 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. 30 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 Brightness Step Formulas: AGL brightness step formulas: the circuit current at each step of a 6.6 A series circuit, and the lamp load
- AGL Series Circuit Load and CCR Sizing Formulas: AGL series circuit formulas: the load of a 6.6 A constant current circuit, the cable loss
- AGL CCR Input Power and Energy Formulas: AGL CCR energy formulas: the input power, apparent power and reactive power of a constant current regulator
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