Architectural lighting analysis for passive systems is not about selecting fixtures — it is about designing the building to be its own light source during daylight hours. The analysis quantifies what the geometry of a project will produce in terms of illuminance, glare, and temporal light variation, before construction begins.
In MÉTODO, lighting analysis is part of the early design process. It shapes the section, the window proportions, and the ceiling height. These are not cosmetic decisions.
What Passive Lighting Analysis Measures
A passive lighting analysis for a residential project produces several distinct measurements:
Daylight factor (DF): the ratio of interior illuminance to the illuminance available outside on an overcast day. Expressed as a percentage. Target values:
- Living and dining rooms: 2% to 5% DF
- Kitchens: 2% minimum
- Bedrooms: 1% to 2% (lower because primary use is evening)
- Corridors and service spaces: below 1% is acceptable
Annual sunlight exposure (ASE): the percentage of floor area that receives more than 1,000 lux of direct sunlight for more than 250 hours per year. High ASE (above 10%) indicates overheating risk or glare risk. Passive design aims to maximize DF while keeping ASE within acceptable range — a constraint that often resolves to carefully sized and oriented windows, not large ones.
Useful daylight illuminance (UDI): the percentage of occupied hours when illuminance falls within the range considered useful — typically 100 to 3,000 lux. Hours above 3,000 lux at the work plane indicate glare risk. Hours below 100 lux indicate insufficient daylight and require artificial supplementation.
The Section Analysis Method
The primary tool for passive lighting analysis in MÉTODO is the section drawing with annotated sun angles. This is not a software output — it is a drawing produced by the architect, showing:
- Sun altitude at solar noon on December 21 and June 21
- Sun altitude at 9 am and 3 pm on the same dates
- The penetration depth of direct sunlight into the room at each of these positions
- The shadow cast by the roof overhang, window sill, and any external shading devices
The section drawing is produced before the computational model. It gives the architect intuitive control over the light — allows quick iteration of window height, sill depth, and overhang dimension before committing to a simulation model.
Once the section is developed, computational simulation confirms the quantitative performance. At this stage, surprises are rare because the geometry has already been rationalized.
Room-by-Room Analysis Logic
Each room type in a residence has a different use schedule and a different tolerance for direct sunlight and glare. The passive analysis must treat each room separately:
Living and dining rooms: occupied primarily in the evening; daylighting is used in afternoon hours. A west-facing living room in a mild climate can work if shaded from direct summer afternoon sun. A south-facing living room in Mexico City works well with an overhang sized for the summer solstice angle.
Kitchen: occupied throughout the day; good DF important. North orientation provides consistent diffuse light without glare at the work surface. East orientation provides morning light during breakfast preparation but requires glare control.
Primary bedroom: used primarily at night and early morning. East orientation provides a natural wake cycle. High DF unnecessary — privacy and blackout capability more important than maximum daylight.
Study and library: requires consistent, high-quality diffuse light for sustained visual tasks. North orientation optimal. Direct sunlight on a reading surface creates high contrast that causes eye fatigue.
Bathroom: natural light reduces humidity and improves sense of cleanliness. A skylight or high window provides light without compromising privacy.
Integration with Passive Thermal Systems
Lighting analysis and thermal analysis are not separate exercises. They are the same exercise looked at from two different perspectives.
A south-facing window that provides useful winter heating also risks summer overheating. The overhang that blocks summer sun changes the DF of the room. A stone floor that provides thermal mass also changes the reflectance characteristics of the room, affecting how light bounces to the ceiling and walls.
In the passive design process, lighting and thermal analysis are run simultaneously because every geometry decision affects both. A window size change to improve DF also changes the heating and cooling load. This is the constraint that makes passive design a design discipline — there is no single correct answer, only a set of trade-offs that must be made explicitly.
The matriz de opciones — the comparison of multiple design options side by side — is the tool we use to make these trade-offs visible and decidable. An option that provides better DF but higher summer heat gain can be compared directly with an option that provides lower DF but better thermal comfort. The client can participate in this comparison rather than accepting a single recommendation.
Próximos pasos
Passive lighting analysis belongs in the early design phase of every residential project where natural light plays a role in the spatial concept. It shapes the form before it confirms the performance.
Conoce el método de MÉTODO to understand how we integrate lighting analysis into the full passive design process from diagram to detail.