A work light wattage rating measures the electrical power the lamp consumes, expressed in watts (W). A typical LED work light draws 18W to 80W; a halogen work light draws 35W to 100W; a xenon (HID) work light draws 35W to 75W. The right wattage depends on the application, the lamp count on the vehicle, the alternator capacity, and the type of lighting technology fitted. Buying too low a wattage produces inadequate light for the task. Buying too high a wattage wastes money, drains the alternator, and risks tripping fuses. This guide covers what wattage means in practice, the lumens output you can expect at each wattage tier, the right wattage for tractor, plant, truck, and farmyard applications, the total system load calculation, and the alternator capacity rules that govern how many work lights you can run together.
What Wattage Measures and What It Does Not
A work light wattage is the power input drawn from the vehicle electrical system. The figure is calculated as voltage multiplied by current. A 40W work lamp at 12V draws approximately 3.3A. A 40W work lamp at 24V draws approximately 1.7A. The wattage stays constant; the current changes with the voltage.
A work light wattage does not directly equal light output. Two 40W lamps from different manufacturers can produce different lumens output depending on LED chip quality, driver efficiency, and lens optics. A premium 40W Cree-chip LED produces approximately 5,000 to 6,000 lumens. A budget 40W generic LED might produce 1,500 to 3,000 lumens at the same rated wattage. The lumens-per-watt efficacy (lm/W) is the better quality indicator.
The relationship between watts and useful light varies by technology. An LED lamp produces approximately 90 to 130 lumens per watt at the chip level (lower at the system level after driver losses, lens losses, and thermal derating). A halogen lamp produces approximately 15 to 25 lumens per watt. A xenon HID lamp produces approximately 50 to 90 lumens per watt. For the same lumens output, an LED draws roughly one-quarter the wattage of a halogen.
Lumens Output at Each Wattage Tier
A work light lumens output depends on the wattage and the technology. The table below shows typical output ranges for premium-quality lamps; budget lamps may achieve 50 to 70% of these figures.
| Wattage | LED (premium) | LED (budget) | Halogen | Xenon (HID) |
|---|---|---|---|---|
| 18W | 1,800 to 2,400 lm | 800 to 1,500 lm | 270 lm | n/a |
| 27W | 2,700 to 3,600 lm | 1,200 to 2,200 lm | 405 lm | n/a |
| 35W | 3,500 to 4,500 lm | 1,500 to 2,800 lm | 525 lm | 3,000 to 3,200 lm |
| 40W | 4,000 to 5,200 lm | 1,800 to 3,200 lm | 600 lm | n/a |
| 55W | 5,500 to 7,200 lm | 2,500 to 4,400 lm | 825 lm | 4,800 to 5,200 lm |
| 60W | 6,000 to 7,800 lm | 2,700 to 4,800 lm | 900 lm | n/a |
| 75W | 7,500 to 9,800 lm | 3,400 to 6,000 lm | 1,125 lm | 6,500 to 7,000 lm |
| 100W | 10,000 to 13,000 lm | 4,500 to 8,000 lm | 1,500 lm | n/a |
| 120W | 12,000 to 15,600 lm | 5,400 to 9,600 lm | n/a | n/a |
| 180W | 18,000 to 23,400 lm | 8,100 to 14,400 lm | n/a | n/a |
The lumens output at 40W LED matches roughly 250W halogen or 75W xenon. This is the headline benefit of LED technology: equivalent light at one-quarter the power draw. For a tractor with 6 work lamps running for 8 hours during harvest, switching from 100W halogen (600W total, 50A at 12V) to 40W LED (240W total, 20A at 12V) frees 30A of alternator capacity for other loads.
Lumens vs Lux: Important Distinction
A lumen is the total light output from a lamp. A lux is the illumination falling on a surface at a given distance. Two lamps of equal lumens output produce different lux readings if their beam patterns differ. A spot beam concentrates 4,000 lumens into a narrow cone and produces high lux at the centre. A flood beam spreads the same 4,000 lumens across a wide area and produces low lux at any single point but covers more ground. See understanding lumens, lux and colour temperature for the full measurement reference.
Wattage by Application
A work light wattage matches the application. Cab roof flood lamps for general fieldwork need different wattage from front grille spot lamps for long-range visibility.
| Application | Recommended LED wattage | Typical lamp count |
|---|---|---|
| Tractor cab roof (general fieldwork) | 27W to 40W per lamp | 4 to 8 lamps |
| Tractor front grille (long-throw spot) | 40W to 60W per lamp | 2 to 4 lamps |
| Tractor rear work lamp (ploughing) | 40W to 80W per lamp | 2 to 4 lamps |
| Combine harvester cab roof | 60W to 120W per lamp | 6 to 12 lamps |
| Telehandler boom (load area) | 27W to 60W per lamp | 2 to 4 lamps |
| Self-propelled sprayer boom | 18W to 40W per lamp | 6 to 12 lamps |
| HGV cab roof (cargo loading) | 40W to 80W per lamp | 2 to 6 lamps |
| Plant machine boom (excavator, wheel loader) | 60W to 120W per lamp | 4 to 8 lamps |
| Forklift safety lamp (forward) | 18W to 40W per lamp | 1 to 2 lamps |
| ATV / UTV work lamp | 18W to 40W per lamp | 1 to 4 lamps |
| Farmyard fixed mast | 80W to 200W per lamp | 1 to 4 lamps |
Tractor Cab Roof Wattage
A tractor cab roof work lamp typically draws 27W to 40W in LED form. The position sits 2.5 to 3 metres above ground and angles down towards the work area or implement. A 27W LED at this position produces enough light for a 5 to 10 metre work area. A 40W LED extends the useful range to approximately 15 metres. A higher wattage adds reach but also adds glare in dust and rain conditions.
A typical modern tractor carries 4 cab roof lamps as standard (2 forward, 2 rearward) with options for 6 or 8 lamps on premium trim. A John Deere 6R, New Holland T6, or Massey Ferguson 5700 in standard trim runs 4 x 40W LEDs (160W total, 13.3A at 12V). The same tractor in premium trim with 8 lamps runs 320W total, 26.7A at 12V.
Tractor Front Grille Wattage
A tractor front grille spot lamp draws 40W to 60W in LED form. The role is forward driving visibility on dark farm tracks and at the field-road interface. The beam is typically spot or driving pattern to extend reach.
A higher wattage (75W to 120W per lamp) suits an LED light bar fitted across the front of the tractor for very long range visibility, but the road-legal status is restricted. See LED light bars road legal UK for the legal use restrictions.
Tractor Rear Work Lamp Wattage
A tractor rear work lamp draws 40W to 80W in LED form. The role is illuminating ploughs, harrows, cultivators, drills, and other implements during night fieldwork. The position sits at the rear cab corners or on a dedicated mast above the rear linkage.
The rear work area is wider than the front work area because implements extend up to 6 metres behind the tractor. The wider beam spread (flood pattern, 60 to 100 degrees) suits this position. Higher wattage adds depth of illumination to the back of long implements.
Combine Harvester Wattage
A combine harvester carries the highest work lamp count and the highest total wattage of any farm machine. A John Deere S700, New Holland CR, or Claas Lexion modern combine carries 8 to 12 cab roof work lamps at 60W to 120W each. The total work lamp wattage on a fully equipped combine reaches 1,000W to 1,500W (83A to 125A at 12V). The combine alternator is sized for this load (typically 200A to 350A).
Plant Machine Wattage
A heavy plant machine (CAT 320 excavator, Volvo L150 wheel loader, JCB JS220) typically runs 24V and carries 60W to 120W work lamps. The higher wattage suits the longer working distances on plant machines and the larger work areas (the bucket position on an excavator can be 6 to 10 metres from the cab).
Calculating Total System Load
A total system load calculation sums the current draw of all work lamps and other electrical loads to confirm the alternator can supply it. The calculation uses the formula: total wattage divided by system voltage equals total current in amps.
Worked Example: Modern Tractor
A John Deere 6155R has a 150A alternator at 14V (running). The standard electrical loads include:
| Load | Current draw |
|---|---|
| Engine ECU and CAN bus | 8A |
| Cab fan and heating | 12A |
| Air conditioning | 15A |
| Dashboard and instrument cluster | 3A |
| Radio and accessories | 4A |
| Wipers and washers (intermittent) | 4A |
| Headlamps (low beam) | 10A |
| Tail lamps and indicators | 4A |
| Base load total | 60A |
This leaves 90A for additional loads (work lamps and implement electronics). A 6-lamp work light fitment at 40W each draws 240W, or 17A at 14V. The same fitment at 60W each draws 360W, or 26A. The same fitment at 100W each draws 600W, or 43A. All three options sit within the 90A headroom.
Adding an electric implement (e.g., a fertiliser spreader with 30A draw) reduces the available headroom for work lamps. The system designer plans for the worst case: all lamps on, all implements on, AC on full, headlamps on dipped beam.
Worked Example: Compact Tractor
A Kubota L3560 has a 40A alternator at 14V. The standard electrical loads total approximately 18A (no AC fitted, simpler ECU). This leaves 22A for additional loads. A 4-lamp work light fitment at 40W LED each draws 160W or 11A at 14V, which sits within the available capacity. The same fitment at 100W halogen each would draw 400W or 28A, which exceeds the available capacity and would discharge the battery during sustained use.
This is why compact tractors and older tractors typically use LED rather than halogen for work lamp fitment. The lower wattage matches the smaller alternator capacity.
Alternator Capacity Rules
A vehicle alternator output limits the total wattage of fitted work lights. The general rule is: total electrical load (work lamps plus base load) must stay below 80% of alternator capacity at idle, and below 90% of alternator capacity at running speed.
| Tractor / vehicle type | Typical alternator | Headroom for work lamps |
|---|---|---|
| Sub-compact tractor (Kubota BX) | 20A to 30A | 4 to 6A (1 x 40W LED) |
| Compact tractor (Kubota L, JD 1) | 40A to 55A | 15 to 25A (4 x 40W LED) |
| Utility tractor (NH T5, MF 4700) | 90A to 120A | 50 to 80A (6 x 40W LED safely) |
| Large tractor (JD 8R, Fendt 900) | 150A to 200A | 100 to 150A (12+ x 40W LED) |
| Combine harvester | 200A to 350A | 150 to 280A (12 x 100W LED) |
| Telehandler | 90A to 120A | 50 to 80A (6 x 40W LED) |
| HGV (24V) | 60A to 150A at 24V | 30 to 100A (6 x 60W LED easily) |
| Heavy plant (24V) | 90A to 200A at 24V | 60 to 150A (12 x 80W LED) |
Halogen vs LED for Alternator Headroom
A halogen work lamp draws 4 times the wattage of an LED equivalent for the same light output. A 100W halogen draws 7A at 14V. The equivalent LED (40W) draws 2.8A at 14V. For a vehicle with limited alternator headroom (compact tractor, older tractor, sub-compact), LED is the only viable choice for multiple work lamps.
For a heritage tractor (Fordson Major, Massey 135, John Deere 2030) with a 30A or 35A alternator, fitting 4 work lamps means committing to LED. Trying to fit 4 x 100W halogens (400W total, 28A) leaves no headroom for any other load and discharges the battery during use. The halogen to LED upgrade guide covers the retrofit detail.
Wattage Matching to Lamp Tier
A work light wattage choice ties to the brand tier and the LED chip quality. A 40W premium-tier lamp produces more light than a 60W budget-tier lamp because the premium chips are more efficient.
For working tractors used daily, the brand tier matters more than the headline wattage. A 27W Hella or Nordic Lights lamp outperforms a 40W cheap eBay import on actual measured output, beam cleanliness, durability, and lifespan. See cheap vs premium LED work lights for the tier comparison and the real-world performance gap.
Watching for Overrated Budget Lamps
A budget lamp specification often overstates the wattage. A lamp marketed as “100W LED” may contain LED chips that physically cannot dissipate more than 30W to 40W; the housing has no heatsinking for 100W of LED output, and the actual continuous draw measures 35W. The output matches the actual wattage, not the marketed wattage.
For accurate specification, ignore the marketed wattage on cheap imports and check actual measured current draw. A genuine 40W lamp at 12V draws 3.3A on a multimeter. A “100W” lamp drawing 3A is actually a 36W lamp.
Practical Wattage Recommendations
A practical wattage recommendation depends on the application and the fitted vehicle. The following defaults serve most UK farm and contracting use cases.
For a standard utility tractor (90 to 200hp) used for general fieldwork, fit 4 to 6 cab roof LEDs at 27W to 40W each, 2 front grille LEDs at 40W to 60W each, and 2 rear work LEDs at 40W to 60W each. Total wattage approximately 250W to 450W (18A to 32A at 14V).
For a compact tractor (20 to 90hp) used for general fieldwork, fit 2 to 4 cab roof LEDs at 18W to 27W each and 2 front grille LEDs at 27W to 40W each. Total wattage approximately 100W to 200W (7A to 14A at 14V).
For a combine harvester used for night harvesting, fit 6 to 12 cab roof LEDs at 60W to 100W each and 2 to 4 long-range driving lamps at 100W to 150W each. Total wattage approximately 600W to 1,800W (43A to 129A at 14V).
For a telehandler used for night yard work and bale handling, fit 2 to 4 boom LEDs at 27W to 60W each and 2 cab roof LEDs at 40W each. Total wattage approximately 150W to 320W (11A to 23A at 14V).
For a heavy plant machine (excavator, wheel loader, dump truck) used for night construction work, fit 4 to 8 LEDs at 60W to 120W each. Total wattage approximately 480W to 960W (20A to 40A at 24V).
Where to Buy and How to Choose
A work light wattage choice ties closely to the application, the alternator capacity, and the brand tier budget. For the wider buying decision, see the work light buyer’s checklist and the LED work lights overview. For voltage-specific selection, see 12V LED work lights and 24V work lights. For beam pattern selection, see work light beam patterns and flood vs spot beam.
Agri Lighting holds UK stock of LED work lights across the 18W to 180W wattage range. Voltage options include 12V, 24V, and dual-voltage 10-30V. Brand tiers from working budget to premium professional are stocked. Same-day dispatch applies to orders placed before 3pm. Browse the full range of LED work lights for current stock.