Please note that this is the second part of a two-part series on Home Lighting Design For Aging Eyes - this is about The Math, the earlier submission is about The Basics. [Hang on mathphobes, this stuff boils down to one number times another number equals a third number - like 2x6=12, like – like that you can take to a lighting professional who can deliver the illuminance goods.]
In Part 1, we were presented with a unique set of rules and restrictions for home lighting design for aging eyes to two purposes. First, to achieve home lighting design standards more suitable to aging eyes (which the literature allows begin to need extra light in their 40s). Second, to translate these new home lighting design standards into numerical targets of common metrics readily identifiable in the retail lighting marketplace.
Common home lighting metrics include lpW (lumens/Watt) which illuminance efficiency data have been around quite a while and CRI and CCT lighting quality data which were hard come-by up until the last few years, as fluorescent makers "warmed up" their bulbs, and, particularly, their compact fluorescent lamps, or CFLs.
Comment: OK, let's try on an example.
A bedroom has an ambient fc target value of 40, i.e., 40 lm/ft squared. That's a given. The bedroom we're targeting in this example is, say, 200 ft squared in floor surface area. 40 lm/ft squared multiplied by 200 ft squared = 800 l, our lumen target.
This house designer is not immediately, if at all, interested in that with which the space gets lighted (noting that method will be specified in the plan set, but rarely materials), except that it be lighted evenly and, by specific instruction, avoid lighting flutter from ceiling fan blades interrupting cast light. He's not interested in specific luminaires (handled broadly in notes attendant to a lighting design schedule) by type, size, or, usually, specific site. Immediately, home lighting designer interest is in determining lumens for given spaces.
Eventually, choosing among materials and methods is for the knowledge of lighting pros and interior decorators and the personal sense of clients, etc.
Comment: Again, it's the lumen number for a space coming from the Rules in Part 1-The Basics that bridges the gap between your lighting interests and intentions and the folks who know a lot about lighting but not a lot about you. At its easiest, bring your lighting professional The Basics and The Math – and the plan set.
These calculations end up in a home lighting design Nightlighting Schedule defining by-level and by-space fc target, actual square feet, lm target, and distinction of task or ambient. Some spaces are necessarily scheduled in more than one line when, for example, task illuminance target varies from, say, shower to vanity – both for different target levels and square footage. Comment: It's labeled "Nightlighting" to oppose it to a "Daylighting" Schedule of natural illumination to interior spaces – separate subject. Nightlighting and Daylighting can interrelate – yet, another subject in residential lighting design.
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