This is about the basics of a unique, self-styled home lighting design guidance system to light home interiors for aging eyes. The aim is to tailor home lighting design practically, not only sensitive to its occupants, but also easily specified and readily recognized in retail settings and by lighting professionals. Separately, Part 2 addresses the math.
Custom home designers should be taking increasing interest in home lighting design and they're not. Mature [that's PC for older] clients [and those who aren't soon will be] eyes, as compared to eyes in youth and early-middle years, need more light and need light presented more selectively.
A standard section of a custom home plan should be an Electrical and Lighting Plan that involves all aspects of this article and its Part 2 partner. Otherwise, there appears to be little guidance that bridges research and hands-on application and buyers are leaving it all up to someone else.
Home lighting "design" often arises from: arbitrary allowance; (sub)minimum standards; personal want, not informed need; poor fundamentals of lighting design; limited forethought; contractor-styled installation; getting the certificate of occupancy; thoughtless grasping
RULES OF HOME LIGHTING DESIGN FOR AGING EYES
Layer lighting: Two-plus layers ambient evenly distributed; not more than two layers task, evenly distributed in utility spaces, such as crafts; absolutely one layer task in strictly utility spaces such as laundry (excluding accent lighting); absolutely one layer task in potentially hazardous spaces such as stairs, workshop, etc. (excluding accent lighting).
Apply dimmer switches wherever possible (Lutron makes applying dimmer switches a whole lot easier than it used to be, including 4-way dimming involving every device in the gang), except in potentially hazardous spaces.
Apply incandescent illumination as a last resort.
Define illuminance on three levels (approximately, not obsessively, allowing to the high side) – 40, 70, 100 foot candles, or lumens/foot squared [or fc, lm/ft squared, respectively, equal and used synonymously throughout this article].
Sidebar: Aspects of home lighting design metrics settled without wiggle-room, to communicate with house lighting pros: Again, 1 fc = 1 lm/ft squared, where foot candle = fc or ftc and lumen = l or lm, which metrics measure illuminance, or the perceived intensity of light or light level. All light bulbs or lamps – incandescent or fluorescent – have illuminance ratings in lumens/Watt (LPW or lm/W or lpW), a measure of illuminance efficiency related to the Watts you pay for in bulb and electricity.
The author derates published lpW by a 0.8 multiplier, or 20% discount, for merchandising hype, resistance wear, and dirt accumulation.
Arrange illuminance so that in-between abutting spaces, the fc change shall be no greater than 30 fc and may grade in levels less than 30 fc in the interims.
Comment: Passage from one light level to another with these rules should naturally offer in almost all cases illuminance level change as a transition and not as a suddenly parted curtain.
Bare bulbs shall not be casually observable (saying brightness and glare are not the same). For specific areas, e.g., hallways, small closets, and most common and private spaces get 40 fc, ambient or task, depending on viewing intensity – e.g., hall, common and private spaces are usually ambient, closets are usually task. For moving-around areas of bathrooms, kitchens and other utility spaces, walk-in closets, most stairways get 70 fc, not more than 40 fc of which is ambient and not less than 40 fc of which is task. For active viewing areas at bathroom and kitchen counters, laundry, workshop, etc. get 100 fc, not more than 40 fc of which is ambient, given 2 special considerations.
Special Home Lighting Design Consideration 1: Measuring 100 fc work areas, as in a kitchen, island, pantry, bathroom, laundry, sewing, game, workshop and the like, includes not less than the work surface area plus 1 linear foot back from it. Strictly utility areas, e.g., laundry, pantry, etc., and, particularly, utility areas with hazard potential, e.g., workshop, such an area's illumination shall be on a single branch and without a dimmer switch.
Special Home Lighting Design Consideration 2: A task area shall be illuminated on a standalone basis at not less than 40 fc of task lighting at the task area (the practical implication of which is that maximum illumination in some task areas is not less than 40 fc + 70 fc = 110 fc). Allowance shall not be reckoned for cabinets and the like that cover relatively high-illuminance surface area, i.e., surface area counts and gets illuminated no matter what.
In functionality - ambient for most spaces; task for work areas; leave most or all dramatic lighting to clients and lighting pros.
In specific formulations of lighting quality (data are approximate) - Ambient means accepting as minimums Color Rendering Index (CRI) over 80, preferably over 90 [available: compact at 80-95, and tube fluorescent at 65-95, and incandescent at 85-99+] and Correlated Color Temperature (CCT) not greater than 3000K (a/k/a Kelvin) [available: compact at 2700-4100 and tube fluorescent at 2700-6500, and tougher for incandescent at 2700-2800]. Task means accepting as maximums CRI to 90, preferably not more than 80 [compact and tube fluorescent, tougher for incandescent] and CCT not less than 3000K [compact and tube fluorescent, but not incandescent as so far researched].
