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While luminaires (light fixtures) are designed primarily to provide illumination that is delivered in a particular way – spotlighting or general illumination, for example,, luminaires intended to provide circadian interventions have to produce light to satisfy a bio-dynamic function; the light acts on the body’s internal systems to produce a response that relates to the circadian cycle. Light distribution is vitally important, as is the colour and wavelength of the light produced.
This is the LightCycles:HOME model specification for circadian illumination.
Luminaire Construction
The luminaire will be ceiling-mounted. It shall consist of four discreet components, each of which will be replaceable in the event of component failure, luminaire damage or refurbishment.
- Luminaire body
- Luminaire optical arrangement (diffuser)
- LED light engine
- LED controls, including wireless interface (Casambi – Bluetooth Low energy mesh, for example)
Luminaire Performance
Colour temperatures:
This is a two-channel luminaire – while it operates in a conventional tunable white fashion, it does not use conventional ‘tunable white’ control platforms.
- The daylight channel provides 6500K colour temperature
- The night-time channel provides 2200-2300K colour temperatuire
Photopic Illuminance
- 6000lm at 6500K (this assumes opal glass / acrylic diffuser. If ‘drumskin shade, then 4000lm)
- 4000lm at 2200-2300K (this assumes opal glass / acrylic diffuser. If ‘drumskin shade, then 2000lm)
Melanopic EDI (equivalent daylight illuminance)
- >300 m-EDI at 6500K (luminaire output – not LED board)
- Tending to <10 m-EDI at 2200K (luminaire output – not LED board)
(measured at 1.4m beneath luminaire; on a 1m radius from the vertical centreline of the luminaire; and measured horizontally on the vertical plane)
Colour rendition:
- 6500K: >Ra90, with ‘full spectrum’ spectral distribution: (consider Seoul Semiconductors ‘Sunlike’ or Bridgelux ‘Thrive’ for reference)
- 2200K: >Ra90
Luminous efficacy:
- 6500K: >100lm/W (source efficacy value)
- 2200K: >100lm/W (source efficacy value)
Operating life:
- 50,000 hours to L70.B50
(L = percentage light output after stated hours: B = percentage unit failures after stated hours)
A note about the latest edition of Building Regulations Part L (2021 with 2023 updates) relating to luminous efficacy:
The non-domestic edition (volume 2) calls for a luminaire providing general lighting to have a luminous efficacy of 95 luminare watts/circuit Watt. Our argument is that circadian lighting cannot be considered as general illumination because of the specific way that light is delivered (on the vertical plane, at the eye of the observer). Therefore, the general lighting requirement cannot hold.
There is an exemption for display lighting that calls for only 80 light source lumens/circuit Watt. This is achievable because it relates to source input, rather than luminaire output.
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