The Light Review has been looking at sealed-for-life luminaires; those fixtures that come out of the brown box and get installed without anyone ever looking inside them, or thinking: What Happens Next?
Richard Hayes has something to say:
As responsible designers we are obliged to design for maintained illuminance. When the Maintenance Interval prescribed in those caluculations is reached then, if luminaires are sealed, the only recourse is to scrap them and install new luminaires. Does the client understand this situation? We suspect not.
Questions are begged here:
- What Maintenance Interval (hence, luminaire life) is assumed and is the client made aware that the CAPEX investment is strictly time limited?
- Has the cost of replacement luminaires after the expiry of the Maintenance Interval been built into the cost analysis of the original project? Was the financial case made to the client and was the client fully aware of the implications of buying and installing new luminaires ?
Monolithic LEDs are sold on the basis that they last for ‘a lifetime’, but we know that lifetime is limited. The assumption in the MF calculation, as stated in both CIE and the new draft of BS EN 12464, is that the MF should be high i.e. 0.8 or above. Even if we accept that LEDs do not ‘fail’ (i.e there are zero ‘deaths’), and the LLMF is 0.95 at 50K or even 80K hours, the RSMF and LMF will still hit 0.8 at less than 30K hours, so in the real world the life of a sealed for life LED will be about 25K hours.
Many older commercial and industrial premises do not have great daylight penetration so lights can be working pretty much from 8am until 5pm. Add weekend and late working operations and the annual use can be around 2000 hours So the real world life of the luminaires is a maximum of about 15 years. But probably more like 10 years.
- LLMF = Lamp Lumen Maintenance Factor
- MF = Maintenance Factor
- RSMF = Room surface Maintenance Factor
- LMF = Luminaire Maintenance Factor
Sealed-for life-luminaires, where there is no possibility of source or gear replacement really worry me in the way they are sold to the uninitiated.
In my local MAT (Multi Academy Trust – most schools will be part of a MAT) we are lucky to have a Governor who can look into things like this; we were approached by a contractor claiming he could replace all of the lights with LEDs and that the energy saving would pay the capital loan. I gave the Head teachers some detailed calculations; the contractor argued, we called a meeting where we said I would be present, and they never turned up! This kind of disinformation needs to be challenged wherever it crops up – consider it our social responsibility, if you like.