www.bregroup.com Lighting in the workplace is it just about vision? Dr Cosmin Ticleanu, BRE
General effects of lighting in buildings Visual task performance Safety and visual perception of potential hazards Visual comfort Visual discomfort linked with red, itchy eyes, headaches, and pains associated with poor body posture Mood and wellbeing
Lighting for health & safety Reducing negative health symptoms Perceiving potential hazards Adequate lighting (HSG 38): Sufficient task illuminance No glare, flicker or veiling reflections No excessive luminance contrasts Appropriate emergency lighting
Lighting conditions to avoid (HSG 38): Insufficient light on the task Uneven lighting Luminaires too bright Daylight openings too bright (windows or rooflights) Excessive range of brightness Bright reflected images adjacent to the task Reduced contrast of task because of veiling reflections Strong shadows on the task Flicker Stroboscopic effects Tasks difficult to see Lighting for health & safety
Minimum lighting for health & safety (HSG 38) Activity Typical examples Average illuminance (lux) General movement Corridors, circulation routes 20 5 Minimum illuminance (lux) Movement in hazardous areas Activity requiring limited perception of detail Activity requiring perception of detail Construction sites, loading bays 50 20 Kitchens, assembly of large components 100 50 Offices, bookbinding, sheet metal work 200 100 Activity requiring perception of fine detail Drawing offices, assembly of electronic components, textile production 500 200
Lighting standards BS EN 12464-1:2011 Light and lighting. Lighting of work places. Indoor work places BS EN 12464-2:2014 Light and lighting. Lighting of work places. Outdoor work places Recommendations for: Maintained illuminance Illuminance uniformity Glare Colour rendering
Example for indoor workplaces Source: BS EN 12464-1:2011
Example for outdoor workplaces Source: BS EN 12464-2:2014
Emergency lighting BS EN 1838:2013 Lighting applications. Emergency lighting BS 5266-1:2016 Emergency lighting. Code of practice for the emergency lighting of premises
Example for emergency lighting Minimum horizontal illuminance of: 1 lux at floor level along centre line of escape route 0.5 lux on the empty floor in open areas Maximum luminous intensity for light sources to limit disability glare Minimum CRI of 40 Minimum luminance of safety signs High risk areas: Minimum maintained illuminance on working plane at least 10% of required task illuminance but at least 15 lux Source: BS EN 1838:2013
Considering the task Task may be located in one part of the space Task may be vertical e.g. viewing display boards, shelves For speaking to other people, cylindrical illuminance at head height may be more important No need for uniform lighting everywhere Consider task lighting Substantial energy savings from task/ambient lighting
Observed Frerquency Occupant preferences Occupants prefer a range of illuminances Use task lighting Give occupants controls, especially dimming controls 140 120 100 80 60 40 20 0 <100 101-200 201-300 301-400 401-500 501-600 601-700 701+ Desktop illuminance (lux)
Considering the task and the space People judge the brightness of a space by looking at the walls Even if task illuminances are adequate, a space may still look gloomy if the walls are too dark Additional light on the walls and ceiling can make a room look much brighter and more welcoming
Glare Disability glare affects the ability to see Discomfort glare causes discomfort without affecting the ability to see Direct glare occurs when the light source is in the field of view Reflected glare occurs when the light source is reflected from surfaces in the field of view
Too high luminance contrasts causing discomfort glare Examples of glare
Too bright light sources causing disability glare for particular view directions Examples of glare
Examples of glare Discomfort glare caused by two high desk illuminances (on average 26% higher than standard recommendation) and too low relative wall illuminances (on average 50% of standard recommendation)
Avoiding glare from electric lighting Disability glare: Aiming light towards areas of interest Using suitable shielding Discomfort glare: Using low luminance luminaires Balanced luminance distribution across space Reflected glare: Correctly arranging VDUs units with respect to luminaires Using matt surfaces rather than glossy finishes Restricting luminaire luminance Using light, high reflectance finishes for ceilings and walls
Avoiding direct glare 10-30 degrees (depending on lamp type) Source: HSG 38
Flicker Critical flicker frequency of human eyes: 60 Hz Flicker of higher frequencies (up to 200 Hz) can still be non-visually detected by the human retina Negative effects include: Visual fatigue Reduced visual performance Eyestrain Headaches Increased heart rate in agoraphobic individuals Sensitivity to flicker varies between individuals; populations more susceptible include children and people suffering from migraine or autism
Flicker Avoiding flicker: Maintaining supply stability Using high-frequency electronic control gear Flicker can still occur when dimming LEDs by means of mains voltage dimmers and drivers DC-based LED drivers can dim the light output of LEDs to less than 1% whilst avoiding the risk of flicker Measuring flicker: Percent flicker Flicker index
Non-visual effects of light Body clock and exposure to artificial light at night Intrinsically photosensitive retinal ganglion cells in the retina (iprgcs) most sensitive to blue light Ongoing research on minimum light level resulting in changes in melatonin level Threshold for suppressing melatonin varies with spectral irradiance: peak at 446-477nm Blue wavelengths (400-500nm) appear to affect alertness, body temperature and heart rate Common cool white LEDs produce significant light output in the 460-500nm range Night-time exposure to any type of cool white light source can be disruptive, not just LEDs
Circadian lighting WELL Building Standard Equivalent Melanopic Lux (EML), a proposed alternative metric weighted to the iprgcs instead of to the cones, which is the case with traditional lux WELL v1 & v2 Electric lighting: At least 150EML for all workstations vertically facing forward at 1.2m above floor level DIN SPEC 67600 & DIN SPEC 5031-100 Daytime: At least 250lux / 8000K at the eye for several hours preferably in the morning Evening: At most 50lux / 2700K at the eye Illuminance adjustments at other colour temperatures / light spectra
Potential health benefits of special types of lighting LEDs can be manufactured to generate light in very specific areas of the spectrum, even in a light that appears white to the naked eye Blue enriched LEDs during daytime can be used to correct disrupted sleep, resynchronize circadian rhythms or increase alertness Short wavelength visible light (450-500nm) can also help to reduce symptoms of SAD Integration with smart controls to create advanced circadian lighting systems
Example of BRE work: Office POE study Problem: too much bright light coming from above Sore eyes and headaches BRE study: In situ measurements (luminaire luminance; surface luminance; desk illuminance; walls and ceiling illuminance; surface reflectance) Computer modelling (UGR) Solution proposed: additional perimeter wall lighting; dimmable lighting; zoned / grouped lighting controls
Example of BRE work: Classroom POE studies T8 direct lighting (magnetic ballasts) or CFL directindirect lighting (electronic ballasts), sometimes dimmable / 3300-4000K Average working plane illuminance: 260-450 lux [300 lux in BS EN 12464-1] Average wall illuminance: 100-180 lux / 345 lux in one case [200 lux in BB90 for 300 lux on horizontal working plane]; 0.3-0.6 of average working plane illuminance [0.5-0.6 in SLL Code for Lighting] Average whiteboard illuminance: 140-160 lux / 330 lux in one case [320 lux in BS EN 12464-1] Cylindrical illuminance: 120-160 lux / 215 lux in one case [150 lux in SLL LG5 at 1.2m above floor level]
Example of BRE work: Research on circadian lighting 23 participants in open plan office Variable lighting administered over several weeks in winter Site measurements, monitoring and computer modelling of lighting Subjective and objective measures of occupant reaction (questionnaires, regular questions and performance tests) Monitoring of level of activity using activity tracking watches Determine how variable lighting impacts on health and wellbeing are linked with control schedules Identify optimal control strategies for circadian lighting and produce associated guidance so that health and wellbeing benefits are maximised
Example of BRE work: Research on biophilic office design Monitoring of light levels Computer modelling of existing electric lighting and daylight distribution Annual profiles of daylight illuminance and total illuminance at eye level Levels of circadian stimulation Liaising with BRE Social Research on occupant surveys BRE Wellness and Biophilia Symposium 6-7 June 2019, BRE Watford
Conclusion Electric lighting should: Meet minimum recommendations for health and safety Meet relevant standard recommendations Provide adequate illumination both for the task and the space Not cause glare and flicker Provide adequate levels of emergency lighting Also consider the non-visual effects of light
bregroup.com Thank you Cosmin.Ticleanu@bregroup.com Dr Cosmin Ticleanu WELL AP MSLL Principal Consultant, Lighting Fire & Building Technology Group BRE Watford, UK WD25 9XX +44 (0)1923 664871 bregroup.com