Why “Ceiling Shadow” Is the Real Retrofit Constraint
When replacing legacy 4-lamp T12 wraparounds, many facilities run into a practical issue: the fixture footprint and lens profile have protected the ceiling from aging and dirt. Installing a smaller fixture often reveals visible “ghosting” around the old housing. If repainting is not an option, the retrofit needs to preserve coverage or use a conversion method that keeps the existing housing footprint.
This guide focuses on retrofit approaches that reduce ceiling disruption while improving efficiency and reducing maintenance exposure.
Evaluate the Existing Housing and Mounting Footprint
- Measure overall housing length/width and mounting hole pattern
- Check ceiling condition outside the lens edge (expect discoloration if the fixture is downsized)
- Confirm whether the housing is structurally sound (rust, deformation, loose mounting)
- Identify existing ballast type and wiring condition
Retrofit Options That Avoid Ceiling Repaint
| Retrofit Method | What Stays | Why It Helps | Primary Risk |
|---|---|---|---|
| LED tube conversion using existing housing | Housing footprint and lens (sometimes) | No ceiling ghosting; fast turnaround | Ballast failures if ballast remains |
| Internal LED retrofit kit (plate/strip) | Housing footprint | Modern LED engine inside old footprint | Requires clean mechanical install and correct driver placement |
| Full fixture replacement with same-size wraparound | Footprint only (matched by size) | New optics without repainting | Must match footprint closely to avoid shadow reveal |
Wiring Choices: Type A, Type B, and Hybrid
For legacy T12 wraparounds, leaving old ballasts in place is often the reliability weak point. If labor access is already happening, many facilities choose ballast bypass to remove a future failure component.
| Tube Type | Electrical Approach | Maintenance Outcome |
|---|---|---|
| Type A | Uses existing ballast | Fast install; ballast remains future failure point |
| Type B | Ballast bypass (line voltage to sockets) | Removes ballast failures; requires correct wiring |
| Type A+B | Can operate with or without ballast | Flexible; still validate actual wiring configuration |
Lens and Diffusion Considerations
- Old wraparound lenses can yellow; reusing a degraded lens can reduce delivered lumens and shift appearance
- A new diffuser/lens can improve visual comfort in corridors and stairwells
- Match lens style to space: harsher optics in stairwells can create perceived glare
Field Steps and Checkpoints
- Photograph the existing fixture footprint before removal to verify coverage targets
- If using Type B, label the fixture as ballast-bypassed and verify socket wiring configuration
- Check grounding and strain relief; poor terminations cause repeat callbacks
- Measure light levels after retrofit at representative points, not directly under the fixture only
Common Failure Points in Wraparound Retrofits
- Leaving aging ballasts in place and treating failures as “tube problems” later
- Downsizing fixture footprint and exposing ceiling ghosting
- Incorrect socket wiring for Type B (leading to non-start or early failures)
- Reusing yellowed lenses that reduce output and create uneven appearance
Related Linear Fixture Categories
If repainting is not an option, preserving the existing fixture footprint is the priority. Housing-based retrofit kits or matched-size wraparound replacements prevent ceiling shadow reveal. Electrical approach selection (especially Type B ballast bypass) determines long-term maintenance outcomes.
Brandon Waldrop
As the lead technical specialist for our commercial lighting technical operations, Brandon Waldrop brings over 20 years of industry experience in product specification, outside sales, and industrial lighting applications.
His career began in physical lighting showrooms, where he focused on hands-on product performance and technical support. He later transitioned into commercial outside sales, working directly with architects, electrical contractors, and facility managers to translate complex lighting requirements into energy-efficient, code-compliant solutions.
Today, Brandon applies that industry experience to architect high-performance digital catalogs and technical content systems, helping commercial partners streamline the specification process and deploy lighting solutions with total technical confidence.
