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

Model scope

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.

• 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.

Units and conventions

• 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.

Inspectable vector

One of 4 source-bound review vectors:

{
  "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."
}

Failure boundary

• 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.

Other records

Sources and evidence

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

• VERIFIED_LEDGER.json
• evidence-tranche5/tranche5-results.json