Source: https://guthlabs.ai/docs/instruments/uv-index-exposure-time-estimator/

instrument / verified-clean

# UV Index Exposure Time Estimator

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/uv-index-exposure-time-estimator/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/uv-index-exposure-time-estimator/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/uv-index-exposure-time-estimator/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/uv-index-exposure-time-estimator/qualification/>)

## Ledger state

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

**Area**: Earth & Space (astronomy, orbital mechanics, meteorology, geology, geodesy, oceanography)

**Tranche**: tranche-7

**Evidence ID**: t7-080

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The supplied rule-of-thumb can be implemented only after explicitly choosing minutes and defining skin_factor as MED/200. It should be labeled as an educational erythema-threshold estimate, not a safe-exposure calculator. For a standards-based calculation, replace the heuristic with t_minutes = MED_J_per_m2/(1.5 × UV_index), while still retaining strong medical and individual-variability warnings.

### Formula and scope findings

- The stated formula is dimensionally ambiguous: the unit of 200 is not specified. The test calculations assume minutes, but the formula would produce a result 60 times smaller if interpreted as seconds.

- The formula is not the standard physical conversion from UV Index to erythemally weighted dose. Using 1 UVI = 0.025 W/m², time in minutes is MED_J_per_m2/(1.5 × UVI), so a 200 J/m² MED gives about 133.3/UVI minutes, not 200/UVI minutes.

- The formula requires an explicit definition of skin_factor. A defensible approximation is skin_factor = MED_for_type/200 J/m², but this is not stated in the specification.

- “Approximate safe exposure time” is misleading: the result estimates time to a possible erythema threshold, not a medically safe exposure duration.

- Fitzpatrick type alone cannot reliably predict individual erythema response; UV spectrum, altitude, cloud cover, reflection, sunscreen, clothing, medications, prior exposure, and individual variability are omitted.

### Unit assumptions

- UV Index is dimensionless.

- For the supplied rule-of-thumb test calculations, 200 is interpreted as 200 minutes for Fitzpatrick type I at UVI 1.

- skin_factor is interpreted as MED_for_skin_type divided by the type-I reference MED of 200 J/m².

- The MED table values are approximate erythemal doses in J/m², not guaranteed individual thresholds.

- If a physically derived result is desired instead, use 1 UVI = 0.025 W/m² and convert seconds to minutes explicitly.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

UV_index = 0 causes division by zero and must be rejected. Additionally, the required Fitzpatrick MED/skin-factor lookup table and output time unit are absent from the specification, so numerical results are conditional on assumed factors and a minutes convention.

## 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": {
    "uv_index": 1,
    "fitzpatrick_skin_type": "I"
  },
  "expected_outputs": {
    "estimated_time_to_erythema_minutes": 200,
    "estimated_time_to_erythema_seconds": 12000
  },
  "reference_data": {
    "skin_type": "I",
    "MED_J_per_m2": 200,
    "skin_factor_relative_to_type_I": 1,
    "rule_of_thumb_base_minutes": 200,
    "source_convention": "MED value: widely tabulated standard Fitzpatrick educational convention; rule-of-thumb base: instrument-stated heuristic, not a medical or SI standard"
  },
  "working": "skin_factor = 200/200 = 1.\\nt_minutes = (200 min / 1) × 1 = 200 min.\\nt_seconds = 200 × 60 = 12,000 s."
}
````

## 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-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`