Source: https://guthlabs.ai/docs/instruments/exposure-value-ev-to-lux-foot-candle-converter/

instrument / verified-clean

# Exposure Value (EV) to Lux/Foot-candle Converter

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/exposure-value-ev-to-lux-foot-candle-converter/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/exposure-value-ev-to-lux-foot-candle-converter/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/exposure-value-ev-to-lux-foot-candle-converter/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/exposure-value-ev-to-lux-foot-candle-converter/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Audio, Music, Photography & Color

**Tranche**: tranche-5

**Evidence ID**: t5-056

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The stated forward formula and foot-candle conversion are reasonable approximate conventions. Review is required because reverse formulas are omitted and because the meaning of converting EV100 to scene illuminance depends on an unstated calibration and measurement convention. The honest label is appropriate but should explicitly state that EV is not universally convertible to illuminance without that convention.

### Formula and scope findings

- The forward convention lux=2.5*2^EV100 is a recognized approximate EV100-to-illuminance relationship, but it is calibration-dependent and must not be presented as an exact physical conversion.

- The specification claims reverse conversion but does not provide the inverse formulas. The required inverses are EV100=log2(lux/2.5), lux=fc*10.764, and EV100=log2((fc*10.764)/2.5).

- EV is ordinarily an exposure-value setting, commonly associated with reflected-light exposure; calling the result scene illuminance requires an explicit incident-light/calibration convention.

### Unit assumptions

- EV100 means EV referenced to ISO 100; no ISO adjustment is applied.

- lux and foot-candle (fc) are illuminance units, with 1 fc=10.764 lux approximately.

- The constant 2.5 has units of lux at EV100=0 and is a photographic calibration convention, not an exact universal constant.

- All inverse logarithm inputs must be strictly positive.

## Boundary hardening

### Recorded hazards

- Reverse conversion is undefined for lux=0, fc=0, or any negative input because log2 requires a strictly positive argument.

- Very large positive EV values can overflow numeric implementations of 2^EV100; very small values can underflow.

- The API should reject negative lux and foot-candle inputs, and should require exactly one primary input mode unless consistency checking is explicitly implemented.

- The rounded factor 10.764 introduces small conversion error; use a documented precision consistently.

- A meter-calibration or incident-versus-reflected-light distinction is required to avoid implying that the estimate is a direct calibrated measurement.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "EV100": 0
  },
  "expected_outputs": {
    "lux": 2.5,
    "fc": 0.232255668
  },
  "working": "2^0=1. lux=2.5*1=2.5 lux. fc=2.5/10.764=0.232255668 fc."
}
````

## Related workflows

No source-defined multi-instrument workflow membership is recorded.

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

- `evidence-tranche5/tranche5-results.json`