Power Draw Comparison: LED, Halogen, and Xenon on 12V and 24V Systems

Vehicle work-light power draw is the current in amperes that a lamp pulls from the tractor electrical system at its rated voltage, and the figure differs markedly between halogen, LED and xenon technologies. A 55W halogen work light pulls 4.6 amps on 12V. A 30W LED, which gives considerably more light, pulls 2.5 amps. A 35W xenon HID pulls about 3 amps in steady state but more during its warm-up. These numbers determine how many lamps an alternator can carry, what cable size the wiring needs, what fuse rating to fit, and how much fuel the lighting load adds over a season. This guide covers the electrical fundamentals, the per-technology amp figures on 12V and 24V, the alternator headroom rules, the wiring and fuse sizing, and the real cost of carrying that load.

How Power Draw Works on a Tractor Lighting Circuit

Power draw on a tractor lighting circuit is the current flowing through the lamp, calculated from the lamp wattage divided by the system voltage. The formula is P = IV, where P is watts, I is amperes, and V is volts. Rearranged for current draw, I = P / V.

A 55W lamp on a 12V system draws 55 / 12 = 4.58 amps. The same 55W lamp on a 24V system draws 55 / 24 = 2.29 amps. Voltage halves the current draw at the same wattage. That is the reason 24V trucks and large tractors run smaller cables and lower-rated fuses than 12V machines for the same lighting output.

Three rules govern lighting current on a vehicle.

1. Total current at any switch or fuse is the sum of every lamp on that circuit.
2. Cable size must carry the steady current plus a 25% safety margin.
3. Fuse rating must protect the smallest cable on the circuit, not the lamp.

LED and xenon work lights complicate the simple formula. LED draw is what the driver pulls from the supply, including the driver’s own losses. Reputable makers normally quote an LED work light’s wattage as its input power, so current is simply rated watts divided by volts, but check the data sheet. Xenon draw varies between cold start and steady state because the ballast forces high current through the bulb to strike the arc.

For a wider view of lighting electrical systems, see 12V vs 24V Tractor Systems and How to Wire Work Lights to a 12V System with a Relay.

Halogen Work Light Power Draw on 12V and 24V

A halogen work light draws current equal to its rated wattage divided by the system voltage, with no driver overhead and a steady amp figure for the life of the bulb. Halogen is the only technology of the three where the printed wattage equals the actual electrical load.

Halogen work-light current draw at 12V.

1. 35W H3 lamp. 2.92 amps at 12V.
2. 55W H3 or H7 lamp. 4.58 amps at 12V.
3. 60/55W H4 dual-filament lamp (high beam). 5.0 amps at 12V.
4. 65W H9 lamp. 5.42 amps at 12V.
5. 100W heavy-duty work lamp. 8.33 amps at 12V.

Halogen work-light current draw at 24V.

1. 35W H3 lamp. 1.46 amps at 24V.
2. 55W lamp. 2.29 amps at 24V.
3. 70W H3 or H7 lamp. 2.92 amps at 24V.
4. 100W heavy-duty lamp. 4.17 amps at 24V.

A bank of 6 by 55W halogen work lamps on a 12V tractor pulls 27.5 amps. The same 6 lamps on a 24V telehandler pull 13.7 amps. Cable and fuse sizing follows. On the cable table below, the 12V bank needs 6mm sq cable and a 30A fuse, while the 24V version can use 2.5mm sq cable and a 20A fuse.

Halogen current draw is constant from cold to hot, which makes sizing simple. Inrush current at switch-on is about 8 to 12 times the steady draw for the first 50 milliseconds, so the fuse must be a slow-blow type to avoid nuisance tripping. For wider context on the technology, see LED vs Halogen Tractor Lights.

LED Work Light Power Draw on 12V and 24V

LED work light power draw is set by the driver electronics, not the LED chips alone, and a quality LED work light delivers the same light for much less supply current than a halogen. The driver converts the supply voltage to the constant current needed by the LED string.

LED work-light current draw at 12V (representative agricultural mid-tier and premium lamps).

1. 18W LED work lamp (1,500 lumens). 1.5 amps at 12V.
2. 27W LED work lamp (2,500 lumens). 2.25 amps at 12V.
3. 30W LED work lamp (2,800 lumens). 2.5 amps at 12V.
4. 48W LED work lamp (4,500 lumens). 4.0 amps at 12V.
5. 60W LED work lamp (6,000 lumens). 5.0 amps at 12V.
6. 100W LED light bar (9,000 lumens). 8.3 amps at 12V.

LED work-light current draw at 24V.

1. 27W LED lamp. 1.13 amps at 24V.
2. 48W LED lamp. 2.0 amps at 24V.
3. 100W LED light bar. 4.17 amps at 24V.

The output gap is what makes LED look so favourable on the alternator. A 55W halogen work lamp delivers about 1,200 to 1,500 lumens for 4.6 amps at 12V. A 27W LED work lamp delivers 2,500 lumens for 2.25 amps at 12V. The LED produces 67% more light for half the current draw. A bank of 6 LED lamps replaces 6 halogen lamps at 13.5 amps instead of 27.5 amps, freeing 14 amps of alternator capacity.

Driver efficiency varies between lamps, and better drivers waste less energy as heat. Higher driver efficiency means less heat in the driver and a slight reduction in supply current for the same light output. For more on tier comparison, see Cheap vs Premium LED Work Lights.

Xenon (HID) Work Light Power Draw on 12V and 24V

A xenon work light draws a high warm-up current for 15 to 30 seconds, then settles to a steady draw set by the ballast. The ballast strikes the arc inside the bulb at 20,000 to 30,000 volts, then maintains it at 80 to 90 volts AC, all driven from the 12V or 24V supply.

Xenon (HID) work-light current draw at 12V.

1. 35W HID lamp, warm-up phase. 6 to 9 amps for the first 15 to 30 seconds.
2. 35W HID lamp, steady state. 3.0 to 3.5 amps at 12V.
3. 55W HID lamp, warm-up phase. 8 to 12 amps for the first 15 to 30 seconds.
4. 55W HID lamp, steady state. 4.6 to 5.2 amps at 12V.
5. 70W HID lamp, warm-up phase. 10 to 14 amps for the first 15 to 30 seconds.
6. 70W HID lamp, steady state. 5.8 to 6.5 amps at 12V.

Xenon (HID) work-light current draw at 24V.

1. 35W HID lamp, steady state. 1.5 to 1.75 amps at 24V.
2. 55W HID lamp, steady state. 2.3 to 2.6 amps at 24V.
3. 70W HID lamp, steady state. 2.9 to 3.25 amps at 24V.

The warm-up surge is the design constraint for xenon wiring and switching. A relay sized only for the steady current can wear out early because of the switch-on surge. Size the relay for the warm-up current, not the steady draw.

Xenon ballast efficiency runs 80 to 88%. The light output per watt at the lamp is 60 to 90 lumens per watt, which sits between halogen and LED. A 35W xenon work lamp produces 3,000 to 3,200 lumens, similar to a 35W to 40W LED work lamp. For the wider xenon technology view, see Xenon Work Lights.

Side-by-Side Power Draw Comparison

The 3 lighting technologies compared at matched lumen output show the practical electrical-load difference for a typical farm work-light position.

Technology	Lamp wattage	Lumen output	12V steady draw	24V steady draw
Halogen	55W	1,200 to 1,500	4.58 amps	2.29 amps
Halogen	70W	1,500 to 2,100	5.83 amps	2.92 amps
LED	18W	1,500 lumens	1.50 amps	0.75 amps
LED	30W	2,800 lumens	2.50 amps	1.25 amps
LED	48W	4,500 lumens	4.00 amps	2.00 amps
Xenon HID	35W	3,000 to 3,200	3.00 amps	1.50 amps
Xenon HID	55W	4,500 lumens	4.60 amps	2.30 amps

For around 3,000 lumens on the work area, halogen needs two 55W or 70W lamps (roughly 9 to 12 amps), against a single 30W LED at 2.5 amps or a 35W xenon at about 3 amps. LED is the lowest-draw option in every comparable output band. Halogen is the worst per-lumen option in every band.

A bank of 6 lamps on a 12V tractor (the six halogens give well under half the light of the LED or xenon banks).

1. Six 70W halogen lamps. 35 amps total steady draw.
2. Six 30W LED lamps. 15 amps total steady draw.
3. Six 35W xenon lamps. 18 amps steady, 36 to 54 amps during the 15 to 30 second warm-up.

The same six positions filled with LED instead of halogen frees 20 amps on the alternator. That headroom matters on older tractors with 60 to 90 amp alternators that are already loaded by cab heating, ECU, GPS and beacon circuits.

Alternator Headroom and Battery Load

Alternator headroom is the difference between alternator output capacity at engine working speed and the total electrical load on the system. Lighting, especially work lighting on banks of 4 to 8 lamps, often pushes a tractor close to or past its alternator capacity.

Alternator output varies widely. Older utility tractors often have small alternators, well under 100 amps (the oldest may have a dynamo), while modern high-spec tractors often have 150 amps or more. Check the rating on the alternator or in the operator’s manual.

A typical modern tractor base load (ECU, ISOBUS, GPS, climate fan, lights on at low setting) sits at 25 to 50 amps. Subtract that from the alternator rating to find the headroom for added work lights. A bank of 6 by 70W halogen lamps (35 amps) on a 90-amp alternator with a 30-amp base load leaves 25 amps of headroom, which is tight. The same bank in LED (15 amps) leaves 45 amps of headroom, which is comfortable.

Battery load matters when the engine is off. A bank of 6 LED work lights run for 30 minutes during a hitching task with the engine off pulls 7.5 amp-hours from the battery. The same job in halogen pulls 17.5 amp-hours. A typical tractor battery holds 100 to 130 amp-hours. The halogen bank (35 amps) would flatten it in around 3 to 4 hours, and it would be too flat to start the engine well before that.

For the wider topic of adding extra lights, see Adding Extra Lights to Your Tractor Without Overloading the Circuit.

Wiring, Fuse and Relay Sizing for Each Technology

Wiring, fuse and relay sizing follows the steady current draw of the lamp bank, with extra margin for inrush current on halogen and warm-up surge on xenon. The cable carries the current, the fuse protects the cable, and the relay switches the load on a low-current trigger.

Cable size by current draw (12V automotive cable, single run under 5 metres).

1. Up to 5 amps. 1.0mm sq cable, 10A fuse.
2. 5 to 10 amps. 1.5mm sq cable, 15A fuse.
3. 10 to 15 amps. 2.5mm sq cable, 20A fuse.
4. 15 to 20 amps. 4.0mm sq cable, 25A fuse.
5. 20 to 30 amps. 6.0mm sq cable, 30A fuse.
6. 30 to 50 amps. 10.0mm sq cable, 50A fuse.

Fuse rating rules.

1. Halogen circuits use a slow-blow fuse to absorb the 50ms inrush surge.
2. LED circuits use a standard automotive blade fuse, sized at the steady draw plus 25%.
3. Xenon circuits need a fuse rated for the warm-up surge, which is 2 to 3 times the steady draw.

Relay sizing.

1. Halogen banks under 20 amps. Standard 30A relay.
2. LED banks under 30 amps. Standard 40A relay.
3. Xenon banks. Use a 40A relay for a single 35W lamp, 50A or solid-state for multi-lamp banks.

A common mistake is sizing a relay for the steady draw of a xenon bank and ignoring the warm-up surge, which wears the contacts early. Solid-state relays cope better with repeated inrush than mechanical relays.

For the full wiring walkthrough, see How to Wire Tractor Lights with a Relay and How to Wire Work Lights to a 12V System with a Relay.

The Real-World Cost of Higher Power Draw

Higher work-light power draw costs money in three ways: extra fuel burn, faster battery wear, and earlier alternator failure. The cost gap between an LED and a halogen banking is small per hour but adds up over a season.

Fuel cost of carrying lighting load. Every 100 watts of constant electrical load adds roughly 0.05 to 0.06 litres per hour to a working tractor’s fuel burn (alternator efficiency 50 to 60%, engine efficiency around 30 to 35%, diesel about 36 MJ per litre). A bank of 6 by 70W halogen lamps adds 420 watts of load, about 0.2 to 0.25 litres per hour. The same bank in LED at 180 watts adds about 0.1 litres per hour. Across 600 working hours a year, the halogen bank burns roughly 70 to 90 extra litres of diesel over LED. Multiply that by your own red diesel price to see the cost.

Battery wear from heavy intermittent draw. Lead-acid batteries lose capacity faster when discharged deeply and often. A 35 amp halogen lighting load with the engine off takes a 100Ah battery flat in about 3 hours. The same job in LED, at 15 amps, takes about 6 to 7 hours. Tractors that often sit with the engine off and lights on (loading, hitching, livestock work) are harder on their batteries with halogen lighting.

Alternator wear. A heavily loaded alternator runs hotter, and running close to its rated output for long periods shortens its life. Cutting the lighting load with LED keeps the alternator further from its limit.

On the fuel figures above, the fuel saving from LED on a 6-lamp bank is modest, tens of litres of diesel a year rather than hundreds. The bigger gains are more light, longer lamp life, fewer bulb changes, and less strain on the battery and alternator. For the practical conversion steps, see how to upgrade tractor lighting from halogen to LED.

For the universal LED work lamps range and the universal halogen work lamps range, browse the shop.