About

Accurate lighting calculation is critical for electrical engineering, architectural planning, and energy auditing. The historical reliance on Wattage W as a metric for brightness is obsolete. Wattage strictly measures power consumption (the rate of energy transfer), whereas Lumens lm measure Luminous Flux (the total quantity of visible light emitted).

The discrepancy arises from the Luminous Efficacy of the source. A standard tungsten filament operates at 10-17 lm/W, wasting 95% of energy as heat. Modern GaN-based LEDs can exceed 150 lm/W. Failure to account for this ratio leads to over-illumination (wasted energy/glare) or under-illumination (safety hazards/strain).

This tool serves as a comprehensive engineering utility. It moves beyond simple multiplication. It incorporates a database of specific bulb profiles (A19, PAR38, T8 High Bays), accounts for Color Temperature K, calculates ROI based on local energy tariffs, and estimates Illuminance lx at specific distances using the Inverse Square Law.

Formulas

The conversion relies on the definition of luminous efficacy η:

Φ_v = P × η

To determine the Illuminance E_v (Lux) at a specific distance r from an isotropic point source, we apply the Inverse Square Law:

E_v = Φ_v4πr²

Note: In practical engineering, for directional lamps (spots), the Beam Angle θ alters this distribution. The simplified cost efficiency model is:

Cost = P × t × Rate1000

Reference Data

Technology	Bulb Shape / Type	Power (W)	Flux (lm)	Efficacy (lm/W)	Lifespan (h)
Incandescent	Standard A19	60	800	13.3	1,000
Incandescent	Candle B10	40	380	9.5	1,000
Halogen	Spot PAR38	90	1,300	14.4	2,500
Halogen	Capsule G4	20	300	15.0	3,000
CFL	Spiral T2	13	900	69.2	8,000
LED (Consumer)	Standard A19	9.5	840	88.4	15,000
LED (High End)	Filament A21	8	1,100	137.5	25,000
LED (Industrial)	Corn Cob (E39)	100	14,500	145.0	50,000
HPS	High Pressure Sodium	400	50,000	125.0	24,000
Metal Halide	Quartz MH	400	36,000	90.0	15,000

Frequently Asked Questions

Lumens measure the total light output from the source in all directions (Luminous Flux). Lux measures the light intensity falling on a specific surface area (Illuminance). 1 Lux equals 1 Lumen per square meter. A bright bulb (high lumens) far away will result in low Lux on your desk.

Industrial LEDs (High Bay, Corn Cob) prioritize thermal management and driver efficiency over size or aesthetics. They use larger heat sinks and higher-quality phosphor coatings, allowing them to achieve 140-160 lm/W, whereas compact home bulbs (A19) are often limited to 80-100 lm/W due to heat constraints.

Yes. Generally, cooler color temperatures (4000K-6500K) are more efficient to produce than warm white (2700K). To create warm light, LEDs use heavier phosphor layers which absorb some blue light, slightly reducing total lumen output by 5-15% compared to a cool white chip of the same wattage.

A 400W Metal Halide produces roughly 36,000 lumens initially but degrades quickly (L70 depreciation). To replace it, look for an LED fixture producing roughly 30,000-36,000 lumens. With typical LED efficacy of 140 lm/W, you would need a 200W-240W LED fixture, saving approximately 40-50% in energy.