BulbBriefHow BulbBrief works
No magic, no black box. Here is exactly how we turn a few answers into one bulb specification — and where the numbers come from.
1. Start with room area
We multiply your room’s length by width to get its area in square feet. (If you enter meters, we convert first: 1 meter = 3.28084 feet.)
2. Apply a lumens-per-square-foot target
Different rooms need different brightness. These ranges are translated from common residential lighting guidance (foot-candle targets expressed as lumens per square foot for ambient light):
| Room | Lumens / sq ft |
|---|---|
| Bedroom, living room, dining room, closet | 10–20 |
| Hallway | 5–10 |
| Laundry room | 20–40 |
| Kitchen, bathroom (ambient) | 30–40 |
| Home office | 30–50 |
| Garage | 50–75 |
Area × that range gives a base total-lumen range for the room.
3. Apply transparent adjustment factors
We multiply the base range by three factors so the result fits your space:
| Factor | Option | Multiplier |
|---|---|---|
| Desired feeling | Cozy and warm | × 0.85 |
| Balanced everyday | × 1.00 | |
| Bright and crisp | × 1.20 | |
| Ceiling height | 8–9 ft | × 1.00 |
| 10 ft | × 1.08 | |
| 11–12 ft | × 1.15 | |
| More than 12 ft | × 1.25 | |
| Room finishes | Light walls/surfaces | × 1.00 |
| Mixed / medium | × 1.08 | |
| Dark walls/surfaces | × 1.18 |
Higher ceilings and darker surfaces absorb or lose more light, so they nudge the target up. Then we divide the adjusted total by your number of fixtures to get a per-bulb range, rounded to sensible 50-lumen increments.
4. Translate to a familiar bulb
We map the per-bulb result to the closest familiar package so you can shop quickly:
| Lumens | Old incandescent feel |
|---|---|
| 450 | ≈ 40-watt |
| 800 | ≈ 60-watt |
| 1,100 | ≈ 75-watt |
| 1,600 | ≈ 100-watt |
| 2,600 | ≈ 150-watt |
We never claim an exact LED wattage, because efficiency varies by product. Always shop by lumens, not LED watts.
5. Color temperature (Kelvin) and CRI
Kelvin describes how warm or cool white light looks — not physical heat. We pick a Kelvin range and one target based on the room and the feeling you chose, leaning warm (2700K) for living spaces and cooler (3500–5000K) for task-heavy rooms like garages and offices.
CRI (Color Rendering Index) measures how true colors look. We recommend 90+ for living spaces, 95+ for color-critical tasks like makeup, and allow 80+ as a budget option in garages and storage.
6. A separate task-light tip
If you tell us the main activity (reading, cooking, grooming, desk work), we do not over-brighten the whole room. Instead we add a separate, clearly-labelled task-light suggestion. Those are practical planning ranges, not professional lighting designs.
Sources and assumptions
BulbBrief’s ranges are practical consumer rules of thumb, not a proprietary or laboratory-grade formula. The lumens-per-square-foot targets reflect widely-published residential guidance derived from illuminance (foot-candle) recommendations, and the lumen-to-incandescent equivalents and “shop by lumens” advice align with U.S. consumer-energy guidance. We consulted the following publicly available, authoritative resources:
- ENERGY STAR — Light Bulbs (lumens vs. watts, choosing efficient bulbs).
- U.S. Department of Energy — LED Lighting (LED efficiency, color temperature basics).
- Illuminating Engineering Society (IES) (the professional body behind recommended illuminance levels that consumer rules of thumb are simplified from).
Key assumptions: typical North American bulb shapes and bases (A19/E26, BR30, G25, B11/E12, GU10); ambient (general) lighting only, with task lighting handled separately; no modeling of window daylight, fixture optics, beam angle, or light depreciation over time; and a coarse light/mixed/dark surface-reflectance factor rather than measured reflectance.
Honesty about limits
This is a good consumer estimate, not an engineering calculation. It does not model window daylight, exact fixture optics, beam angles, or light-loss over time. For complex spaces, layered designs, or anything involving wiring, consult a qualified electrician or lighting designer.