― Metric

Daylight is about location, intensity, time of day and duration of the exposure.

A surface receives light from a source

like the sun and reflects it to a receiver

like our eyes as illuminance measured in lux.

A light source, the sun emits a luminous flux in all directors

with intensity. 


The intensity is determined by the time of day or altitude

and the season or azimuth as it moves from east to west.

Our eyes receive the

reflected light from the source.


Illuminance measures the intensity of incident light on a surface.  Typically, it is between 300 lux and 3000 lux for daylight design.  For children, adjust the threshold to 500-2000 lux.

Spatial Daylight Autonomy, sDA

sDA provides the percentage of the regularly occupied space that receives 300 lux for 50% of the operational hours.  For children, adjust it to 500 lux.

Useful Daylight Illuminance, UDI

UDI measures the percentage of a regularly occupied space’s operational hours is within the target thresholds.  Adjust the threshold for children to 500-2000 lux than typically the case for adults.

Daylight Glare Probability, DGP

DGP provides an index for the perceived glare from daylight at a point in time, position in space, and view angle.   It is typically maintained at less than 40% to minimize disturbing and intolerable glare.

Equivalent Melanopic Lux, EML

Equivalent Melanopic Lux (EML) measures the intensity of non-visual light that impacts our circadian rhythm at a particular point in time, position in space, and view angle. For children, maintain 200 EML for at least 75% of the regularly occupied spaces in the morning.

Correlated Color Temperature, CCT

CCT measures the color distribution that a light source emits.  It impacts their performance, alertness, and visual comfort level for children.  Note the range of colors: warm white light 3000 k; cool white light 4000k;  and 6500k or higher with artificial light.