Equipment / lighting
Driver and Efficiency of Caving Headlamps
Technical guide to caving headlamp efficiency: 1S to 4S battery architectures, buck/boost/linear drivers, and their real impact on runtime and carried weight.
Why efficiency matters in real use
Higher efficiency means more useful light for the same onboard energy. In practice, it avoids carrying “dead” battery mass and extends useful runtime on levels that are actually used underground.
Typical efficiency by driver technology
When architecture allows it, pure buck or pure boost usually provides the best peak efficiency. Buck-boost is very useful over wide voltage ranges, but often loses a few points at the best operating point.
| Driver technology | Typical useful range in headlamps | Possible maximum (best point) | Current behavior | Practical reading |
|---|---|---|---|---|
| Pure buck | ~90-96% | up to ~98% | Low: fixed losses stand out. Mid: best efficiency zone. High: thermal and conduction losses rise. | Excellent when battery voltage stays above LED forward voltage plus margin. |
| Pure boost | ~88-95% | up to ~97% | Low: fixed losses hurt efficiency. Mid: often very good. High: thermal and conduction losses increase. | Very good when battery voltage is below target LED voltage. |
| Buck-boost (non-inverting) | ~85-94% | up to ~97% | Low: efficiency is more modest. Mid: good compromise. High: may drop earlier than pure buck/boost depending on design. | Very flexible across voltage, usually a bit less efficient than a well-sized pure buck/boost in daily use. |
| Linear | ~65-90% | close to Vf/Vbatt | Efficiency mostly follows Vf/Vbatt ratio. As current and heat rise, losses become critical. | Simple and clean regulation, but losses rise quickly with a larger battery/LED voltage gap. |
Battery architecture and efficiency impact
Key point: increasing cell count in series at equal output lowers current. Lower current cuts losses across the chain (battery, cables, connectors, driver, thermal path), improving global efficiency and stability.
| Battery architecture | Typical matching drivers | Typical efficiency range | What changes underground |
|---|---|---|---|
| 1S (1 cell: 18650/21700) | Boost, buck-boost, sometimes linear per channel | ~75-95% | Simple logistics. Good weight/runtime compromise when regulation is well designed. |
| 2S (2 cells in series or equivalent pack) | Mainly buck, sometimes linear | ~80-96% in switching, more variable in linear | Lower battery current at equal output: fewer losses and easier thermal management. |
| 3S (3 cells in series) | Mainly buck | ~85-96% | Even lower current, lower I2R losses system-wide. Effective for sustained high levels. |
| 4S / multi-cell pack | Buck, more integrated architecture | ~86-96% when well implemented | Minimum current-related losses at equal output, excellent long-run stability; tradeoff is pack weight/cost. |
LED count impact on efficiency
| Optical/electrical choice | Efficiency effect | Field consequence |
|---|---|---|
| Single LED driven hard | Lm/W drops quickly at high LED current, then drops again with heat. | Faster stepdown and shorter useful runtime at high mode. |
| Two LEDs sharing current (flood/spot or mixed) | Each LED runs at lower current: better lm/W and slower thermal degradation. | Real gain: better sustained intermediate levels and more stable runtime. |
| Well-driven multi-LED setup | Can deliver best system efficiency if channels and cooling are well controlled. | Excellent versatility and global efficiency, otherwise gains shrink when driver/thermal design is limited. |
Model details (comparison driver and efficiency column)
| Model | Pack / battery architecture | Driver (current state) | Retained efficiency range | Technical rationale | Runtime / weight impact |
|---|---|---|---|---|---|
| Stoots Yeti | 1x21700 (1S) | Regulated switching (manufacturer claim) | eta ~85-92% | Stoots publishes ~85% (PWM boost) and up to 92% on combined architecture. Lower bound kept to cover non-optimal operating points. | Very good useful-energy to carried-mass ratio. |
| Scurion 1500 caving | 4-cell pack (multi-cell) | Switching (published as “up to”) | eta ~88-94% | Scurion publishes >94% (upper bound). Lower bound estimated for real operating points away from optimum. | Very energy-efficient, but heavier total system. |
| Meandre Prowide 4.5 | 3 cells in series (3S) | Likely switching | eta ~85-92% | 3S pack favors efficient buck regulation, but no detailed published driver curve. | Good sustained output, noticeable system weight. |
| Petzl DUO RL | Proprietary multi-cell pack | Likely switching regulated driver | eta ~78-90% | Petzl documents regulated output but does not publish detailed per-mode driver efficiency: conservative estimated range. | Strong runtime, with pack weight and cost to account for. |
| Armytek Wizard C2 Pro Max LR | 1x21700 (1S) | Likely switching | eta ~75-88% | No detailed manufacturer efficiency curve on the product page: estimated range from regulated 1S architecture. | Good global efficiency/price, low carried mass. |
| Phaeton Dual | 2x18650 (often 2S depending on setup) | Linear (retained main case) | eta ~65-90% | With linear regulation, efficiency mostly follows Vf/Vbatt, so it varies with mode and state of charge. | Can regulate smoothly, but thermal losses are higher at strong output. |
| Argolamp 2.0 | 2x21700 (2-cell pack) | Linear (retained main case) | eta ~65-90% | Same logic as Phaeton in linear mode: efficiency depends on pack voltage vs LED voltage. | Good capacity runtime, but real efficiency varies with selected mode. |
| Sofirn HS20 | 1x18650 (1S) | Mixed architecture depending on channels (order of magnitude) | eta ~60-80% | Budget multi-channel positioning: efficiency varies more with mode and thermal behavior. | Light and affordable, but useful runtime at high mode is more limited. |