Lighting adequacy calculator

“How many light fixtures will I need for this room, to ensure sufficient lighting?”

Interior designers notoriously ignore this question.   Homeowners and apartment-dwellers don’t know how to project lighting needs.   The result is trial-and-error:  (1) install/plug in the lamps and fixtures you have, (2) wait for nightfall to assess whether the room feels well-lit, (3) order more lights, (4) reassess.   This unscientific approach is inefficient – and can be disastrous in a kitchen renovation, where most light fixtures are hard-wired, and must have been specified upfront in the room design.

I developed this lighting adequacy calculator to eliminate the guesswork!

Some important concepts:

  • Lighting is the single most impactful interior design element in any room.  Change the lighting, change your experience of the space!  Don’t skimp on adequate amounts of beautiful, varied and well-distributed lighting.
  • Wall color has a huge impact on how much light you need.  Dark walls require more light, in order to yield the same effect to your eyes.  (Dark walls with adequate lighting creates a beautifully glamorous ambience.  Consider how many high-end restaurants employ this approach.)
  • Lampshades have a huge impact on how much light you need.  Putting a lampshade over a bulb reduces the amount of light that reaches your eyes.   Theoretically, lampshades are an absurd concept, reducing the efficacy of the light you (and the earth) are paying to produce… in order to produce comfortable and pleasing light.  (Black fabric shades on table lamps and sconces are a hallmark of high-end interior design, adding high drama to a bedroom or living room.)
  • Combine (a) always-on (when the room is occupied) ambient lighting with (b) task lighting.  This gives you lots of optionality to dynamically match lighting with how the room is being used.  (Also, use dimmers liberally and ensure most lights are individually controllable.)
  • Sophisticated and pleasing lighting schemes include light coming from many directions (down from ceiling fixtures, across from floor lamps and sconces, up from table lamps) and of multiple qualities (intense light from bare bulbs, soft light filtered through glass fixtures, mood light escaping from around opaque fabric lampshades).
  • The older you get, the more light you need to feel that a room is well-lit.   Err on the side of more lighting – and especially more task lighting – if you have any trouble reading.  Insufficient lighting makes people feel tired.
  • Lighting requirements depend greatly on what the room is used for. Kitchens require much more light per square foot than do living rooms. Bathrooms need as much light as kitchens, but less of it needs to be task lighting.  Over-lit restaurants with harsh, bare bulb lighting are uncomfortable, unromantic and can easily kill the business.
  • Light produced by a lightbulb is measured in lumens.  Adequate lighting means your lighting scheme is producing adequate lumens (conditioned by wall color and fixture shading). A lightbulb consumes a certain number of watts (electricity) to produce those lumens (visible light output), depending on the type of bulb.  For simplicity, this calculator asks you to input all of your lighting in terms of the nominal watts consumed by the bulb (i.e., the watts listed on the bulb).  The calculator automatically indexes all lighting to “incandescent equivalent watts” using each bulb type’s lumens-per-watt efficiency.

How to use the calculator:  Input the nominal watts for all of your planned or existing light sources.   Compare the resulting “Effective Watts” of your current lighting scheme to the theoretical “Target Effective Watts” figure.  Do you have enough ambient lighting, enough task lighting, and thus enough overall lighting?

Lighting Adequacy Calculator
  Room type:  
  Square feet:  
  Wall color:  
 
  Nominal watts of light fixture Effective watts Target effective watts

("Effective watts" are incandescent-equivalent watts, adjusted for the shade opacity).

Ambient lighting (always on during occupancy)
  Incandescent
  Bare bulb 645
  Light shade 0
  Medium shade 0
  Opaque shade 92
  Low-voltage halogen
  Bare bulb 0
  Light shade 0
  Medium shade 0
  Opaque shade 0
  CFL
  Bare bulb 63
  Light shade 0
  Medium shade 0
  Opaque shade 0
  LED
  Bare bulb 90
  Light shade 0
  Medium shade 0
  Opaque shade 0
  Total ambient light 891 1225
  Ambient light per square foot 2.5 3.5
 
Task lighting
  Candles (number of wicks) 1  
  Incandescent
  Bare bulb 0
  Light shade 0
  Medium shade 0
  Opaque shade 0
  Low-voltage halogen
  Bare bulb 434
  Light shade 0
  Medium shade 0
  Opaque shade 0
  CFL
  Bare bulb 63
  Light shade 41
  Medium shade 0
  Opaque shade 0
  LED
  Bare bulb 0
  Light shade 0
  Medium shade 34
  Opaque shade 0
  Total task light 891 1225
  Task light per square foot 891 1225
 
Total light 891 1225
Total light per square foot 891 1225
 

  |   Email Email

This entry was posted in <5 min read, Design and aesthetics, Interactive calculators, [All posts]. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *