Good lighting puts the right amount of light where people need it, without glare, dark patches or wasted energy. The amount of light, measured in lux, is only one part of it. Uniformity, glare control, light on walls and ceilings, colour quality and controls decide whether a space feels comfortable and works for the tasks done in it.
Measuring light
- Lumens measure how much light a source or luminaire gives out.
- Illuminance, in lux (lumens per square metre), is how much light falls on a surface. One footcandle is about 10.76 lux, and older drawings and many light meters still use footcandles.
- Luminance is how bright a surface looks from a given direction. It depends on the light falling on it and how reflective it is. A white wall and a dark carpet under the same illuminance look very different.
- Efficacy, in lumens per watt, describes how efficiently a luminaire turns electricity into light.
Lighting levels are usually specified as illuminance on a working plane, often desk height for offices and floor level for corridors and warehouses. A light meter at that height measures it directly.
How much light is needed
Recommended illuminance depends on the task, the age of the occupants and how critical accuracy is. The Illuminating Engineering Society publishes recommended values for a wide range of spaces, and designers in Canada commonly use them. General office work typically calls for a few hundred lux on the desk, corridors and storage areas need much less, and detailed inspection or fine assembly needs much more. Older eyes need more light for the same task, which matters in seniors' housing and in workplaces with an older workforce.
Other requirements also apply. Building codes set minimum levels for egress routes and emergency lighting, occupational health and safety rules in each province address workplace lighting, and energy codes such as the National Energy Code of Canada for Buildings, where adopted, limit the lighting power that can be installed per square metre. A design has to satisfy all of these together.
More than brightness
Uniformity
The eye adapts to the brightest thing in view. A desk lit well in one spot and poorly a metre away is tiring to work at, and dark patches in a warehouse aisle can hide hazards. Designers check the ratio between the average and the minimum illuminance across the area.
Glare
Glare comes from bright sources in the field of view: a bare LED, a luminaire seen at a low angle across a large room, or reflections on screens. It reduces visibility and causes discomfort. Shielding, diffusers, luminaire placement and the angle at which light leaves the fixture all control it. Unified glare rating (UGR) is one common measure for indoor spaces.
Vertical light and room surfaces
Spaces where only the floor and desks are lit tend to feel gloomy, even at the recommended desk illuminance. Light on walls and ceilings makes a room feel brighter and helps people see faces, which matters in meeting rooms, classrooms and healthcare spaces.
Colour
Two properties describe the colour of light from a source:
- Colour temperature, in kelvin, describes whether white light looks warm (yellowish, lower kelvin) or cool (bluish, higher kelvin). Warmer light is common in residential and hospitality spaces, and neutral to cooler light in offices, schools and industry.
- Colour rendering, commonly given as CRI, describes how accurately colours look under the light compared with a reference. Retail, healthcare and any task involving colour judgement need good colour rendering.
Mixing colour temperatures in one space looks untidy. Specify one value, and check that replacement lamps and fixtures match.
How a lighting design comes together
- Understand the space and its users. What tasks happen where, at what times, by whom, and what is wrong with the current lighting if there is any.
- Set the criteria. Target illuminance for each area, uniformity, glare limits, colour temperature and rendering, emergency lighting, and the energy code limit.
- Select luminaires. Choose fixtures for distribution, glare control, efficacy, maintenance access and appearance.
- Calculate. Lighting software models the room with its surface reflectances and produces illuminance grids. A maintenance factor allows for light output falling over time and dirt on fixtures.
- Add controls. Occupancy sensing, daylight dimming and scheduling, as required by the energy code and as suits the use. See lighting controls.
- Verify. After installation, measure light levels, confirm the controls work as intended and adjust settings.
A typical case
A small accounting office has complaints about tired eyes and a dull, gloomy feel, even though a light meter shows the desks are well lit. A walk-through shows why. The old troffers put light straight down, so the walls and ceiling are dark. Several fixtures near the windows are seen at a low angle by staff facing them and reflect in monitors. And when some lamps were replaced, a cooler colour was used, so the room has two different whites. The redesign uses luminaires that put some light on the ceiling and walls, a lower overall illuminance than before on the desks with better uniformity, one colour temperature throughout, and daylight dimming near the windows. The office ends up using less power for lighting and staff find it more comfortable.
Common mistakes
- Designing to a single lux number and ignoring glare and walls
- Over-lighting, which wastes energy and often increases glare
- Choosing fixtures for appearance alone without checking distribution
- Not allowing for light loss over time, so levels fall below target in a few years
- Ignoring screens, which reflect bright fixtures
- Leaving controls uncommissioned, so sensors switch lights off on occupied rooms
Do not forget the emergency side. Normal lighting design and emergency lighting have to work together. Egress routes need the illuminance the building code requires during a power failure, and tests should confirm it. See emergency lighting and exit sign testing.
How ehZee can help
Our lighting design and controls work starts with how the space is used and what is wrong with it today. We set the criteria, select fixtures, run the calculations and design the controls, and drawings for permit are sealed by a licensed professional engineer where required.
Common questions
Can I check light levels myself?
Yes, with a reasonable light meter held at the working height. Take readings across the area, not just under fixtures, and note the time of day, since daylight affects results.
Is more light always better?
No. Beyond what the task needs, extra light wastes energy and often increases glare. Quality and distribution usually matter more than raw quantity.
What colour temperature should an office use?
Neutral white is common in offices, but the right choice depends on the space, the finishes and the occupants' preference. What matters most is using one value consistently.
Why do LED fixtures sometimes look harsher than the old ones?
Many LED fixtures have small, very bright light sources. Without good diffusers or shielding, they can produce more glare than older fluorescent fixtures at the same light level. Choosing fixtures with good optics, and checking glare in the design, avoids this.