About

Understanding brightness in the era of energy-efficient lighting requires shifting from "Watts" to "Lumens" (lm). While Watts measure energy consumption, Lumens measure the total amount of visible light emitted. This tool serves two distinct purposes: estimating brightness for consumer bulbs (LED, CFL, Incandescent) and performing strict photometric conversions for lighting engineers.

For directional light sources, such as spotlights, the relationship between luminous intensity (Candelas) and total flux (Lumens) depends on the beam angle. A focused beam concentrates light, resulting in high intensity but potentially lower total flux compared to an omnidirectional bulb. This calculator handles both scenarios.

Formulas

1. Physics Conversion (Candelas to Lumens):

Luminous flux depends on the solid angle Ω.

Φ_v = I_v × Ω

Where the solid angle for a cone with apex angle θ is:

Ω = 2π(1 − cos(θ2))

2. Wattage Estimation:

Lumens ≈ Watts × Efficacy lm/W

Reference Data

Technology	Est. Efficacy (lm/W)	10W Equivalent	60W Equivalent	Lifetime (Avg)
Incandescent	12 - 17	140 lm	800 lm	1,000 hrs
Halogen	16 - 24	200 lm	950 lm	2,500 hrs
CFL (Fluorescent)	50 - 70	600 lm	3000 lm (approx 45W)	10,000 hrs
LED (Standard)	80 - 100	900 lm	5000 lm (approx 50W)	25,000+ hrs
LED (High Eff.)	130+	1300 lm	N/A	50,000 hrs

Frequently Asked Questions

A traditional 60-watt incandescent bulb produces approximately 800 lumens. To replace this with an LED, look for a bulb rated at 800 lumens (usually consumes about 8-10 Watts).

Lumens measure the total light output of the source. Lux measures how much of that light actually lands on a specific surface area. 1 Lux = 1 Lumen per square meter.

Yes and no. A bulb emits a fixed amount of lumens (total light). However, narrowing the beam angle increases the Candelas (intensity) in that specific direction, even if the total Lumens remain constant.

LED technology improves rapidly. An older LED might output 80 lumens per watt, while a modern high-end diode can exceed 150 lumens per watt. We use an average standard of 90 lm/W for calculations.