Runway Lighting
Touchdown Zone (TDZ) Light for Airfield Ground Lighting
Enhanced visual guidance within the touchdown zone of the runway
Touchdown Zone (TDZ) lights provide enhanced visual guidance within the touchdown zone of precision approach runways during the critical landing phase. Precision AGL Solutions supplies TDZ lighting configurations selected against runway classification, approach category, barrette arrangement, spacing, optical direction, photometric requirements and the approved runway lighting layout.
Supplied by Precision AGL Solutions
Product Overview
Touchdown Zone (TDZ) Light
What It Does
Touchdown Zone (TDZ) lights provide enhanced visual guidance within the touchdown zone of the runway, supporting pilots during the critical landing phase where precise longitudinal and lateral visual information is required.
TDZ lighting forms part of the advanced runway visual-aid system used on precision approach runways and is particularly important for operations requiring enhanced visual cues in reduced-visibility conditions.
The final TDZ arrangement should always be established from the approved aerodrome design, applicable standard and project lighting layout.
Selected According To
- Runway classification
- Precision approach category
- Runway length
- TDZ marking arrangement
- Light-bar / barrette configuration
- Fixture spacing
- Optical direction
- Light colour
- Photometric requirements
- Inset installation requirements
- Series-circuit characteristics
- Pavement and housing arrangement
- Project technical specification
TDZ Lighting Applications
Where TDZ Lights Are Used
Precision approach runwaysPrimary application of TDZ lighting.
Category II approach systemsTouchdown-zone lighting for CAT II operations.
Category III approach systemsTouchdown-zone lighting for CAT III operations.
Low-visibility operationsRunway operations in reduced visibility.
Enhanced touchdown-zone guidanceAdditional visual cues in the touchdown area.
Precision runway rehabilitationReinstatement during runway rehabilitation.
Runway lighting upgradesModernised AGL systems and upgrades.
New precision runway installationsTDZ lighting for new precision runways.
Replacement of existing TDZ fixturesLike-for-like and upgraded replacement.
ICAO provisions identify TDZ lighting for the touchdown zone of precision approach runways Category II or III. TDZ lights may also be fitted on Category I runways where the approved design calls for them. ICAO also describes a separate, simpler “simple touchdown zone lights” arrangement (Annex 14 Chapter 5, simple touchdown zone lights) for other runways; that is not what this page covers.
Function of TDZ Lighting
A Complete Visual Guidance System
What the Lights Do
The touchdown area is one of the most operationally critical portions of the runway. TDZ lights provide additional visual cues that help pilots assess the runway surface and touchdown area during the landing approach.
TDZ lighting should be considered a complete visual guidance system, not simply a collection of individual light fittings.
Effectiveness Depends On
- Fixture location
- Barrette arrangement
- Longitudinal spacing
- Lateral spacing
- Light colour
- Optical direction
- Beam distribution
- Light intensity
- Fixture alignment
- Pavement installation
- Electrical circuit performance
- Maintenance condition
TDZ Light Configuration
Paired Barrette Arrangement
ICAO Arrangement
The TDZ system consists of rows of light barrettes arranged symmetrically about the runway centreline.
Under ICAO provisions, the pattern is formed by pairs of barrettes symmetrically located about the runway centreline. The lateral spacing between the innermost lights of the pair corresponds to the selected touchdown-zone marking spacing. Longitudinal spacing between pairs may be 30 m or 60 m, with 30 m spacing noted as advantageous for lower-visibility operations.
A TDZ barrette is composed of at least three lights, with the lights spaced no more than 1.5 m apart, and the barrette length is between 3 m and 4.5 m.
Typical TDZ Layout Concept
The exact number of barrettes, spacing and total longitudinal coverage must follow the applicable runway standard and approved project drawing.
Longitudinal Coverage & FAA Arrangement
Runway Length and Governing Standard Control the Layout
ICAO Longitudinal Coverage
Under ICAO provisions, TDZ lights extend from the threshold for a longitudinal distance of 900 m, except on runways shorter than 1,800 m, where the system is shortened so that it does not extend beyond the runway midpoint.
This makes runway length an important parameter during product selection and layout engineering.
FAA TDZ Arrangement
For FAA-designed systems, AC 150/5340-30J describes touchdown zone lighting as two rows of transverse light bars located symmetrically about the runway centreline. The guidance specifies:
- Light bars perpendicular to the runway centreline
- Three unidirectional lights per light bar
- Lights facing the landing threshold
- Coverage extending to 3,000 ft, or one-half runway length for runways shorter than 6,000 ft
- First light bars located 100 ft from the threshold
- Light beams toed four degrees toward the runway centreline (AC 150/5340-30J); confirm against the approved drawing
Because dimensional and configuration details can vary between governing standards, the project jurisdiction and approved design standard must control final layout selection.
Optical Direction
TDZ Fixtures Are Directional Lighting Equipment
Optical Characteristics
The optical system should provide the intended light output toward the landing aircraft while controlling the beam distribution in the required viewing region.
- Unidirectional light output
- Direction toward the landing threshold
- Controlled beam distribution
- Horizontal coverage
- Vertical coverage
- Optical axis
- Light intensity
- Colour performance
- Toe-in angle where applicable
Why Orientation Matters
FAA installation guidance (AC 150/5340-30J) calls for the TDZ light beam to be toed four degrees toward the runway centreline. The FAA fixture type L-850B is supplied toed left, toed right or straight, so confirm the correct handing for each row against the approved drawing.
Incorrect fixture orientation can significantly affect the effectiveness of the visual guidance system.
Light Colour
Fixed Unidirectional Lights Showing Variable White
ICAO Colour Requirement
ICAO specifies TDZ lights as fixed unidirectional lights showing variable white.
The selected fixture must therefore provide the required colour characteristics over the specified intensity range.
Technical Review Should Verify
- Colour
- Chromaticity
- Directionality
- Intensity
- Beam distribution
- Intensity-step behaviour
- Optical consistency across the barrette
Inset Installation
In-Pavement Installation Within the Runway Movement Area
Inset / In-pavement
TDZ lights are associated with in-pavement / inset installation, allowing the fixtures to operate within the runway movement area.
The complete installation should be engineered as a coordinated pavement, mechanical, optical and electrical system.
A Typical Installation May Include
- Inset TDZ fixture
- Light housing
- LED / light-source assembly
- Optical lens
- Mounting hardware
- Gasket / sealing system
- Drainage arrangement
- Secondary cable
- Isolating transformer
- Primary circuit connection
Pavement Installation Requirements
Installation Quality Directly Affects Reliability
Fixture Seating
The fixture should be correctly seated within the housing.
Alignment
The optical direction must match the approved TDZ arrangement.
Pavement Level
The finished installation should satisfy the applicable fixture and pavement requirements.
Drainage
Water accumulation around the fixture and housing should be prevented through the approved drainage arrangement.
Sealing
Correct gaskets and sealing components are essential for controlling moisture ingress.
Cable Routing
Secondary cables should be correctly routed and protected from mechanical damage.
Installation Depth & Housing
Take Dimensions From the Approved Installation Drawing
Technical Submission Should Identify
- Fixture overall dimensions
- Housing dimensions
- Housing depth
- Installation depth
- Pavement cut-out
- Mounting-hole arrangement
- Fastener details
- Drainage requirements
- Secondary cable routing
- Maintenance access
Why It Matters
Installation depth is an important selection parameter for TDZ fixtures.
The final dimensions must be taken from the approved manufacturer installation drawing.
Photometric Performance
TDZ Lights Are Precision Photometric Equipment
| Parameter | Engineering Requirement |
|---|---|
| Light source | LED or approved technology |
| Colour | Variable white / applicable requirement |
| Intensity | Standard / project specific |
| Beam distribution | Fixture-specific |
| Horizontal coverage | Applicable requirement |
| Vertical coverage | Applicable requirement |
| Optical direction | Landing-direction specific |
| Toe-in | Where applicable |
| Colour coordinates | Applicable standard |
| Intensity steps | Where applicable |
| Fixture alignment | Critical |
| Photometric verification | Project dependent |
A TDZ fixture that is electrically operational is not necessarily photometrically compliant.
LED Technology
LED Light Source
Potential Advantages
- Long operating life
- Reduced lamp replacement
- Reduced routine maintenance
- Stable optical performance
- Controlled beam distribution
- Improved energy efficiency
- Consistent colour output
- Compatibility with modern AGL monitoring systems
Compliance Is Not Automatic
Modern TDZ systems may incorporate LED technology. However, LED technology should not be treated as the sole compliance criterion.
The complete optical assembly, electrical characteristics, mechanical design and photometric output must satisfy the applicable requirements.
Electrical Characteristics
AGL Series Circuit Arrangement
Constant Current Regulator → Primary AGL Cable → Isolating Transformer → Secondary Cable → Inset TDZ Light
Parameters to Verify
- Rated series-circuit current
- Isolating transformer requirement
- Secondary electrical characteristics
- Power consumption
- Connector arrangement
- Cable interface
- Intensity control
- Circuit monitoring
- Insulation characteristics
Why the Whole Chain Matters
Product selection should consider the fixture together with the isolating transformer, secondary connection and CCR-operated series circuit. Incorrect compatibility can result in:
- Incorrect light intensity
- Improper intensity control
- Excessive electrical loading
- Transformer stress
- Circuit instability
- Premature fixture failure
- Monitoring abnormalities
The electrical performance of the complete system should be evaluated during design, testing and commissioning.
Construction & Environment
Mechanical Construction and Environmental Performance
Mechanical Construction
Depending on manufacturer and fixture design, TDZ lights may incorporate:
- High-strength fixture body
- Inset housing
- Optical lens
- LED module
- Optical reflector / assembly
- Gaskets
- Sealing components
- Fasteners
- Secondary cable interface
- Drainage provisions
Verify exact materials, dimensions and construction from the manufacturer's approved TDS and installation documentation.
Environmental Performance
TDZ fixtures operate in a demanding airport environment and should be evaluated for:
- Water ingress
- Dust
- Humidity
- Temperature variation
- UV exposure
- Corrosion
- Vibration
- Mechanical impact
- Pavement loading
- Aircraft tyre loading
- Cleaning chemicals
For inset installations, the principal reliability considerations are water ingress + drainage + sealing + pavement interface + mechanical loading.
Commissioning & Testing
Verify Fully During Commissioning
Visual Inspection
- Fixture condition
- Lens condition
- Fixture seating
- Housing condition
- Barrette alignment
- Optical direction
- Pavement interface
- Fasteners
- Gaskets
- Drainage
- Connector condition
- Moisture evidence
Electrical Testing
Depending on the approved project test procedure:
- Circuit continuity
- Insulation resistance
- Transformer verification
- Secondary connection
- Series-circuit current
- CCR operation
- Intensity-step operation
- Monitoring operation where applicable
Photometric Verification
Where required, verify:
- Colour
- Intensity
- Beam distribution
- Optical direction
- Toe-in / alignment
- Barrette alignment
- Colour consistency
- Overall photometric performance
TDZ Inspection & Maintenance
Evaluate the Complete TDZ Installation
Optical
- Lens cleanliness
- Lens damage
- Light output
- Colour
- Beam direction
- Optical contamination
Mechanical
- Fixture seating
- Housing
- Fasteners
- Gaskets
- Pavement condition
- Mechanical damage
Electrical
- Isolating transformer
- Secondary cable
- Connector
- Series-circuit current
- Insulation condition
- Moisture evidence
Drainage
- Housing drainage
- Blockage
- Water accumulation
- Mud / debris
- Seal deterioration
Common Failure Modes
Typical TDZ Problems
| Symptom | Possible Causes |
|---|---|
| TDZ light OFF | Open series circuit; failed light source; isolating transformer fault; connector failure; secondary cable fault; internal fixture failure |
| Low light output | Incorrect CCR intensity; optical contamination; LED degradation; damaged optical component; electrical mismatch; fixture alignment issue |
| Intermittent operation | Loose connection; moisture ingress; connector deterioration; transformer connection problem; internal fixture fault |
| Incorrect optical direction | Incorrect installation orientation; fixture movement; incorrect optical assembly; incorrect replacement component; pavement / housing installation error |
| Uneven TDZ appearance | Individual fixture intensity variation; incorrect fixture type; incorrect intensity setting; contaminated optics; alignment error; failed or degraded fixtures |
Engineering Troubleshooting Sequence
A Systematic Approach for a Failed TDZ Fixture
CCRVerify output
Primary series circuitCheck circuit
Isolating transformerCheck transformer
Secondary cableCheck cable
ConnectorCheck connector
TDZ fixtureCheck fixture
Light sourceInspect
Optical assemblyInspect
Barrette alignmentVerify
Photometric verificationConfirm output
This sequence helps identify whether the failure originates in the electrical circuit, fixture, optics or installation.
Product Selection Checklist
Before Ordering TDZ Lighting, Confirm
- Airport / project
- Runway identification
- Runway length
- Precision approach category
- TDZ requirement
- TDZ marking arrangement
- Barrette configuration
- Number of light units per barrette
- Longitudinal spacing
- Lateral spacing
- Required light colour
- Optical direction
- Beam distribution
- Toe-in requirement
- Intensity requirement
- Intensity steps
- LED / approved light source
- Series-circuit current
- Isolating transformer
- Connector type
- Housing type
- Installation depth
- Pavement cut-out
- Mounting details
- Drainage requirements
- Environmental requirements
- Applicable standard
- Manufacturer TDS
- Photometric documentation
- Compliance / type-test documentation
- Project approval requirements
Technical Submittal
Technical Documents to Request
For technical approval and procurement, request:
- Product datasheet
- Technical specification
- Photometric data
- Beam distribution diagram
- Colour / chromaticity information
- Barrette arrangement information
- Electrical specification
- Power consumption
- Operating current
- Isolating transformer requirement
- Connector details
- Housing drawing
- Fixture dimensions
- Installation depth
- Pavement cut-out details
- Mounting details
- Toe-in requirement
- Weight
- Material specification
- Environmental rating
- Installation manual
- Maintenance manual
- Compliance certificates
- Type-test reports
- Warranty information
Standards & References
Governing Standards
Select, install and test in accordance with the applicable edition of the governing aerodrome standards and approved project specification.
- ICAO Annex 14 — Aerodromes, Volume I, 9th Edition (July 2022) with Amendment 18 (visual-aids provisions applicable from 27 November 2025). ICAO also lists Corrigendum No. 2 (18 March 2026) and No. 3 (8 June 2026) to Volume I; check them for the provisions you rely on. Verify the edition adopted by your project
- Applicable ICAO touchdown-zone lighting provisions
- FAA AC 150/5340-30J — Design and Installation Details for Airport Visual Aids
- FAA AC 150/5345-46F – runway light fixtures, including L-850B, the in-pavement runway touchdown zone fixture (unidirectional white; L-850A is the runway centreline fixture, not the TDZ fixture)
- DGCA India requirements, where applicable
- Applicable Indian Standards
- Airport-specific technical specifications
- Approved runway lighting layout
- Approved AGL drawings
- Manufacturer installation instructions
FAA AC 150/5340-30J is an active FAA advisory circular covering airport visual-aid installation details, while FAA AC 150/5345-46F is the current active FAA specification for runway, taxiway, heliport and vertiport light fixtures.
See the ICAO Annex 14 Guide and FAA AGL Guide for background.
Important: Always verify the governing standard edition and project-specific requirements before procurement.
FAQ
Touchdown Zone (TDZ) Light — Frequently Asked Questions
What are touchdown zone (TDZ) lights?
TDZ lights give enhanced visual guidance within the touchdown zone of a precision approach runway during the critical landing phase, and are particularly important for operations requiring enhanced visual cues in reduced visibility. They should be treated as a complete visual guidance system, not a collection of individual fittings.
Which runways need TDZ lighting?
ICAO provisions identify TDZ lighting for the touchdown zone of precision approach runways Category II or III, and TDZ lights may also be fitted on Category I runways where the approved design calls for them. ICAO also describes a separate, simpler arrangement called simple touchdown zone lights for other runways, which is not what this product covers.
How is an ICAO TDZ light pattern arranged?
The system consists of rows of barrettes arranged in pairs symmetrically about the runway centreline. The lateral spacing between the innermost lights of a pair corresponds to the selected touchdown-zone marking spacing, and longitudinal spacing between pairs may be 30 m or 60 m, with 30 m noted as advantageous for lower-visibility operations. A barrette has at least three lights spaced no more than 1.5 m apart, with a length of 3 m to 4.5 m.
How far along the runway do TDZ lights extend?
Under ICAO provisions they extend from the threshold for 900 m, except on runways shorter than 1,800 m, where the system is shortened so that it does not extend beyond the runway midpoint. Under FAA AC 150/5340-30J, coverage extends to 3,000 ft, or one-half the runway length for runways shorter than 6,000 ft, with the first light bars 100 ft from the threshold.
How does the FAA arrangement differ?
FAA AC 150/5340-30J describes two rows of transverse light bars located symmetrically about the runway centreline, perpendicular to the centreline, with three unidirectional lights per bar facing the landing threshold and beams toed four degrees toward the runway centreline. The governing standard and the approved design control the final layout, so confirm against the approved drawing.
What colour are TDZ lights?
ICAO specifies TDZ lights as fixed unidirectional lights showing variable white. The selected fixture must provide the required colour characteristics over the specified intensity range.
Why does fixture orientation and toe-in matter?
TDZ fixtures are directional, and incorrect orientation can significantly affect the effectiveness of the visual guidance system. The FAA fixture type L-850B is supplied toed left, toed right or straight, so confirm the correct handing for each row against the approved drawing.
Which FAA fixture type is used for TDZ lights?
The in-pavement runway touchdown zone fixture is the L-850B (unidirectional white) under FAA AC 150/5345-46F. The L-850A is the runway centreline fixture, not the TDZ fixture.
What does an inset TDZ installation involve?
A typical installation includes the inset fixture, light housing, LED or light-source assembly, optical lens, mounting hardware, gasket and sealing system, drainage arrangement, secondary cable, isolating transformer and primary circuit connection. Fixture seating, alignment, pavement level, drainage, sealing and cable routing all affect reliability, and installation depth and pavement cut-out must come from the approved manufacturer installation drawing.
Is an electrically working TDZ light automatically compliant?
No. A TDZ fixture that is electrically operational is not necessarily photometrically compliant, and LED technology should not be treated as the sole compliance criterion. The complete optical assembly, electrical characteristics, mechanical design and photometric output must satisfy the applicable requirements.
What should I check when a TDZ light is off or its output is low?
Work through the chain: verify the CCR output, check the primary series circuit, the isolating transformer, the secondary cable and connector, then the fixture, light source, optical assembly and barrette alignment, and finally confirm photometric output. Low output can come from an incorrect CCR intensity, optical contamination, LED degradation or an alignment issue. See the L-830 isolating transformer page.
What should be confirmed before ordering TDZ lighting?
Confirm the runway identification and length, the precision approach category, the TDZ marking and barrette configuration, the number of lights per barrette, longitudinal and lateral spacing, colour, optical direction and toe-in, intensity steps, series-circuit current, isolating transformer and connector type, housing and installation depth, drainage requirements and the governing standard, and request the photometric documentation and type-test reports.
Why Precision AGL Solutions
A Complete-System Approach
Precision AGL Solutions evaluates TDZ lighting as part of the complete Airfield Ground Lighting system. Our technical approach connects:
Runway Geometry → TDZ Markings → Barrette Layout → Fixture → Optics → Housing → Transformer → Connector → Series Circuit → CCR → Photometry → Maintenance
This system-level approach helps ensure that the selected TDZ product is compatible with the runway configuration and intended operational requirement.
Procurement Information for Indian Projects
Indian public tenders commonly ask for the documents below. State which ones your tender requires when you send the enquiry, so they are covered in the quotation.
- Manufacturer / OEM authorisation
- Country of origin and local-content declaration (for Make in India purchase preference)
- Type-test and routine-test certificates, and the FAA / ICAO / IEC compliance documents named in the specification
- Datasheets, drawings and installation instructions
- Warranty, delivery period and spares support
- GeM catalogue or tender-portal requirements, where applicable
Need the Right Touchdown Zone (TDZ) Light?
Have a runway lighting requirement? Send us your runway configuration, runway length, approach category, existing TDZ arrangement, TDZ marking layout, approved runway lighting drawing, BOQ, technical specification, required fixture quantity, series-circuit information and housing details where available. We can review it and identify the appropriate TDZ lighting configuration for the project.
- Emailprecisionaglsolutions@gmail.com
- Websiterahulsharmaagl.in
- LinkedInPrecision AGL Solutions
- Phone+91 98214 96412
Engineering Note
Touchdown Zone lighting is a safety-critical visual-aid system in which barrette arrangement, fixture spacing, colour, optical direction, photometric performance, pavement installation and series-circuit operation must work together.
The correct product is therefore not simply a “TDZ light”; it is the correct TDZ fixture and installation configuration for the approved runway design and governing standard.
Product Disclaimer
Product availability, configuration, dimensions, electrical characteristics, photometric performance, certifications and compliance status depend on the selected manufacturer and project specification. The technical values published on this page should not be treated as a substitute for the manufacturer's current approved Technical Data Sheet.
Final selection shall be based on the approved project specification, applicable aviation standards, authority requirements, manufacturer documentation and site conditions. Use of this page is also subject to the Legal Notice, Disclaimer & Terms of Use.
Standards and editions referenced on this site are listed on the Standards Reference page.