This document discusses current and potential new metrics for evaluating daylighting in buildings. It begins by looking at the daylight factor approach and its components. It then explores the potential of volumetric lighting metrics like cylindrical and cubic illuminance. Challenges are discussed, such as how metrics break down in open-plan spaces. A new metric, mean room surface exitance, is proposed and its benefits explained. A pilot study on this and other metrics using a real building is described. The conclusion covers difficulties validating new metrics and need for more case studies.

1. Exploring Daylight Metrics
Longyu Guan
Jemima Unwin

2. Part 1: A look at current daylight metrics
Part 2: The potential of volumetric lighting metrics
Part 3: Challenges and ongoing research of new metrics
Exploring Daylight Metrics

3. Daylight Factor approach:
𝐷𝐹 = (
𝐸 𝑖𝑛
𝐸 𝑜𝑢𝑡
) x 100%
𝐸𝑖𝑛
𝐸 𝑜𝑢𝑡
Overcast Sky
A look at current daylight metrics

4. 𝐷𝐹
Direct
Component
External Reflected
Component
Internal Reflected
Component
Overcast Sky
A look at current daylight metrics
Daylight Factor approach:
𝐷𝐹 = (
𝐸 𝑖𝑛
𝐸 𝑜𝑢𝑡
) x 100%

5. Overcast Sky
A look at current daylight metrics
Daylight Factor approach:
𝐷𝐹 = (
𝐸 𝑖𝑛
𝐸 𝑜𝑢𝑡
) x 100%
𝐷𝐹
Direct
Component
External Reflected
Component
Internal Reflected
Component

6. Overcast Sky
A look at current daylight metrics
Daylight Factor approach:
𝐷𝐹 = (
𝐸 𝑖𝑛
𝐸 𝑜𝑢𝑡
) x 100%
𝐷𝐹
Direct
Component
External Reflected
Component
Internal Reflected
Component

7. Overcast Sky
In real life practice…
Climate-based Daylight Modelling
• Daylight autonomy
• Useful daylight illuminance
• Annual sunlight exposure
Climate Data
Similar process &
the same “working plane”
A look at current daylight metrics

8. Working environment
in the 1970s
Working environment
nowadays

9. Working Plane
“Visual Performance”
Perceived Daylight Adequacy
Whole Space
“Volumetric”

10. Cylindrical illuminance:


2
D
ISin
Ecyl 
EN 12464-1 (2002)
‒“Working plane” removed
‒Recommended illuminance on major room surfaces
‒Mean cylindrical illuminance (2011)
The potential of volumetric lighting metrics

11. Cylindrical illuminance:


2
D
ISin
Ecyl 
1.2 m
EN 12464-1 (2002)
‒“Working plane” removed
‒Recommended illuminance on major room surfaces
‒Mean cylindrical illuminance (2011)
The potential of volumetric lighting metrics

12. Cylindrical illuminance:


2
D
ISin
Ecyl 
1.6 m
EN 12464-1 (2002)
‒“Working plane” removed
‒Recommended illuminance on major room surfaces
‒Mean cylindrical illuminance (2011)
The potential of volumetric lighting metrics

13. Cubic Illuminance
′𝐸 𝑋 = 𝐸 𝑋+ − 𝐸 𝑋−
′𝐸 𝑌 = 𝐸 𝑌+ − 𝐸 𝑌−
′𝐸 𝑍 = 𝐸 𝑍+ − 𝐸 𝑍−
𝐸 =
2
′𝐸 𝑋
2
+ ′𝐸 𝑌
2
+ ′𝐸 𝑍
2
The potential of volumetric lighting metrics

14. Can we make volumetric lighting metrics simpler?
Cubic Illuminance
The potential of volumetric lighting metrics
′𝐸 𝑋 = 𝐸 𝑋+ − 𝐸 𝑋−
′𝐸 𝑌 = 𝐸 𝑌+ − 𝐸 𝑌−
′𝐸 𝑍 = 𝐸 𝑍+ − 𝐸 𝑍−
𝐸 =
2
′𝐸 𝑋
2
+ ′𝐸 𝑌
2
+ ′𝐸 𝑍
2

15. Exitance
Incident flux
Exitance= E ∙ R (lm/m2, lux)
The potential of volumetric lighting metrics

16. Incident flux
Exitance
Average exitance of all Room surfaces
Exitance= E ∙ R (lm/m2, lux)
The potential of volumetric lighting metrics

17. MRSE =
Es∙Rs∙As
Ar
MRSE
Mean Room Surface Exitance (MRSE)
Exitance= E ∙ R (lm/m2, lux)
The potential of volumetric lighting metrics

18. Why MRSE has good potential as a daylight metric
1. A new term, but established concept
Overcast Sky
MRSE
IRC
The potential of volumetric lighting metrics

19. 2. Simplicity
• One single number
Why MRSE has good potential as a daylight metric
1. A new term, but established concept
The potential of volumetric lighting metrics

20. • One single number
• Can be easily calculated (to a first approximation)
Total flux entering the room
(Φ)
Room surface area & reflectance
(Ar & R)
𝑀𝑅𝑆𝐸 =
𝛷𝑅
𝐴 𝑟 1 − 𝑅
2. Simplicity
Why MRSE has good potential as a daylight metric
1. A new term, but established concept
The potential of volumetric lighting metrics

21. 3. Correlates well with electrical lighting guidance
EN12464-1
(Lighting of indoor work places)
Recommends
illuminance on
major room
surfaces
Reflectance of
room surfaces
Effectively forced a
minimum MRSE value
2. Simplicity
Why MRSE has good potential as a daylight metric
1. A new term, but established concept
The potential of volumetric lighting metrics

22. So far we only considered daylighting in a “box”…
However in real life…

23. So far we only considered daylighting in a “box”…
However in real life…However in real life…

24. Problems with MRSE approach:
Challenges and ongoing research of new metrics
MRSE starts to break down when the building is
open-planned and geometrically more complicated

25. Essence of MRSE:
MRSE
𝐄 𝐙+
𝐄 𝐙−
𝐄 𝐘−
𝐄 𝐘+
𝐄 𝐗+
𝐄 𝐗−
Cubic Illuminance
Challenges and ongoing research of new metrics

26. Cubic Illuminance
𝐄 𝐙+
𝐄 𝐙−
𝐄 𝐘−
𝐄 𝐘+
𝐄 𝐗+
𝐄 𝐗−
Challenges and ongoing research of new metrics
Essence of MRSE:

27. Direct Illuminance
Indirect Illuminance
Cubic IlluminanceIndirect Illuminance
Challenges and ongoing research of new metrics
Essence of MRSE:

28. Cubic Illuminance Indirect Illuminance
Challenges and ongoing research of new metrics
Essence of MRSE:

29. Indirect Illuminance
Challenges and ongoing research of new metrics
Essence of MRSE:

30. Indirect Illuminance
Challenges and ongoing research of new metrics
Essence of MRSE:

31. Indirect Illuminance
Challenges and ongoing research of new metrics
Essence of MRSE:

32. Average Indirect Illuminance (of the space)
Indirect Illuminance
Challenges and ongoing research of new metrics
Essence of MRSE:

33. Average Indirect Illuminance (of the space)
Challenges and ongoing research of new metrics
Essence of MRSE:

34. A pilot study on the new metrics:
• The Heelis building
(HQ of national trust)
Challenges and ongoing research of new metrics

35. Scale 1 to 7:
• How is the lighting overall?
• How is the natural lighting overall?
• Is there any glare from natural lighting?
Plus respondents’ comments
Respondents’ working desk can be traced
back.
A pilot study on the new metrics:
• The Heelis building
• BUS datasets
Challenges and ongoing research of new metrics

36. - Daylight Factors (DF) & Average Indirect Illuminance (AIE)
- Overcast Sky with external illuminance of 10,000 lx
A pilot study on the new metrics:
• The Heelis building
• BUS datasets
• Computer simulation (Radiance)
Challenges and ongoing research of new metrics

37. DF: 7.2%
AIE: 164 (1.6%)
DF: 2.1%
AIE: 75 (0.7%)
DF: 5.2%
AIE: 213 (2.1%)
Heelis Building-Data source: Roderic Bunn BSRIA/UCL
0%
10%
20%
30%
40%
50%
60%
1 2 3 4 5 6 7
0%
10%
20%
30%
40%
50%
60%
1 2 3 4 5 6 7
0%
10%
20%
30%
40%
50%
60%
1 2 3 4 5 6 7 ratings
ppl %
Challenges and ongoing research of new metrics

38. • AIE encourages shading + large window
• AIE encourages high room surface reflectance
• AIE represents daylight in the whole space
• Reasons to believe AIE better reflects people’s
perception of daylight adequacy
Challenges and ongoing research of new metrics

39. Difficulties of testing new metrics:
- Data selection
Further research:
- More real life case studies
- Compare the performance of different daylight metrics
- Explore the CBDM potential of new metrics
Metrics can only be reliably tested in many real buildings
- Validity
- Comparing different metrics What should I
have for lunch?
Pfffff… just tick
the middle score
Challenges and ongoing research of new metrics

40. Thank you & Questions?
Jemima.unwin@ucl.ac.uk
longyu.guan.13@ucl.ac.uk