Liquid Penetrant Testing (PT) – Level 1 Certification Course - Equipment, Consumables, and Systems
Proper lighting is crucial in PT because the entire inspection is visual. If you can’t see the indication clearly, you can’t evaluate the part correctly.
Lighting requirements depend on the type of penetrant used:
| Penetrant Type | Required Light Source |
|---|---|
| Type 1 – Fluorescent | UV-A light (black light, ~365 nm) |
| Type 2 – Visible | White visible light (natural or artificial) |
Fluorescent penetrants glow under ultraviolet-A light, typically at 365 nm wavelength. The glow reveals the flaw.
| Type | Notes |
|---|---|
| Mercury vapor lamp | Traditional, high output, fragile |
| LED UV-A lamp | Modern, portable, low heat |
| Filtered black light | Ensures only UV-A is emitted |
✅ Always use filtered UV-A light to avoid violet or visible light contamination.
| Standard | Minimum Intensity Requirement |
|---|---|
| ASTM E1417 / ISO 3059 | 1000 µW/cm² at 38 cm (15") from surface |
| CGSB 48.9712 | Matches ASTM/ISO standards |
Use a UV radiometer to verify intensity.
Maintain 38 cm (15 inches) from inspection surface
Ensure the area has even coverage
Avoid hot spots or shadows
Visible dyes (Type 2 penetrants) do not fluoresce and must be inspected under white light.
| Standard | Minimum Intensity |
|---|---|
| ASTM E1417 / CGSB | 1000 lux (93 foot-candles) |
| ISO | Same, measured at surface |
✅ Measured with a lux meter or calibrated light meter.
LED shop lamps
Fluorescent tubes
Halogen lights
Natural daylight (if intensity is adequate and stable)
❗ Avoid mixed lighting during fluorescent inspection (e.g., don’t inspect under UV + ambient light at the same time).
A proper inspection area or “darkroom” is required for Type 1 fluorescent PT.
| Requirement | Notes |
|---|---|
| Blackout curtains/walls | Prevent ambient light entry |
| Matte black surfaces | Reduce reflections and glare |
| UV-safe warning signage | Warn others to wear PPE |
| Fixed or portable UV lamp | Position overhead or hand-held |
| Light intensity test area | A dedicated spot to check UV output |
Warm up UV lamps for 5 minutes before inspection
Re-measure intensity daily or before each shift
Keep booth clean and dry
Use non-fluorescent cleaning agents to avoid background glow
| Tool | Purpose |
|---|---|
| UV radiometer | Measures UV-A intensity in µW/cm² |
| Lux meter | Measures visible light in lux or foot-candles |
| Black light meter | Optional, may be built into UV lamp |
Turn on the lamp and let it stabilize
Place meter at 15 inches (38 cm) from surface
Record readings at different spots across the inspection area
Compare results with standard requirements
Document the measurement if required by procedure
✅ Replace lamps or filters if output falls below 1000 µW/cm² or 1000 lux
Though UV-A is less harmful than UV-B or UV-C, prolonged exposure can cause eye and skin damage.
Wear UV-rated safety glasses or face shields
Limit time inside UV-lit areas
Use warning signs: “UV LIGHT IN USE – PROTECTIVE EYEWEAR REQUIRED”
Do not point UV lamps toward the face or skin
Regularly inspect UV lamp housing and filters for cracks or clouding
| Setup Type | Advantages | Disadvantages |
|---|---|---|
| Fixed Booth | Stable lighting, ideal for labs | Not mobile, requires space |
| Portable | Used in field inspections | Harder to control environment |
| Hybrid | Light tents, enclosures | Medium setup, transportable option |
✅ In all cases, light intensity must be verified on-site.
Fluorescent PT requires UV-A light, minimum 1000 µW/cm²
Visible dye PT requires white light, minimum 1000 lux
Use a UV radiometer or lux meter to verify lighting before inspection
Fluorescent PT must be performed in a controlled darkroom or enclosed booth
Lighting safety includes PPE, signage, and exposure limitation