Can any one tell me where I can find a formula for determining lighting requirements for specific areas? I have a patio that measures 35' wide and 20' deep at a country club. The owner wants 2 - 100 watt metal halide wall packs mounted 8' high on the building wall. Seems like too much light to me. Thanks.
Candle power
- Thread starter jazzman
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Using wall packs will probably give you about 10 footcandles - plenty for dining/drinking on a patio.
HOWEVER - that is the average value, there will probably be 40 footcandles close to the fixtures, and 1 footcandle at the edge - poor uniformity. Another major problem is Glare. If your back it to the lights, and I'm across the table from you, I probably can't see your face.
If it's an uncovered patio, that might be his only real choice, though. If it is covered, consider fluorescent - more uniform, better color, less glare, about the same total watts.
Formula - ONE FOOTCANDLE = ONE LUMEN PER SQUARE FOOT
In the above example, initial lumens for a 100 watt metal halide lamp = 8500.
8500 x 2 = 17000 total lamp lumens.
Only about less than half of those lumens get out of the fixture and onto the tables - so - 17000 x 0.4 = 6800 lumens 'on the task'.
6800 lumens divided by 700 square feet = 9.7 Lumens Per Square Foot.
9.7 lumens per square foot - 9.7 Footcandles.
(Average Illuminance)
db
HOWEVER - that is the average value, there will probably be 40 footcandles close to the fixtures, and 1 footcandle at the edge - poor uniformity. Another major problem is Glare. If your back it to the lights, and I'm across the table from you, I probably can't see your face.
If it's an uncovered patio, that might be his only real choice, though. If it is covered, consider fluorescent - more uniform, better color, less glare, about the same total watts.
Formula - ONE FOOTCANDLE = ONE LUMEN PER SQUARE FOOT
In the above example, initial lumens for a 100 watt metal halide lamp = 8500.
8500 x 2 = 17000 total lamp lumens.
Only about less than half of those lumens get out of the fixture and onto the tables - so - 17000 x 0.4 = 6800 lumens 'on the task'.
6800 lumens divided by 700 square feet = 9.7 Lumens Per Square Foot.
9.7 lumens per square foot - 9.7 Footcandles.
(Average Illuminance)
db
pbeasley
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My suggestion, pick a couple brands that you like to work with, find out who the local representative is, and give them a call.jazzman said:
weressl
Esteemed Member
jazzman said:
That depends largely on the fixture, how it distributes the light and what is the task at hand. If there is going to be poker-play on the deck, the light may not even be enough. Remember several issues when somebody does the actual calcs for you - factory rep or distributor.
- How even the light distribution will be, the smaller the number of the bright/low results are, the better your distribution is?
- If these are wallpacks, what is the color/reflectance of the wall? What is the dirt factor they use? This would be an adjustment factor to use when the luminaires optics get dirty in cut down considerably on the light output.
- Use average maintained luminance instead of initial.
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HB-9-00 List Price: $425.00
Member Price: $250.00
The IESNA Lighting Handbook is an indispensable reference for industry professionals and is known as the "Bible of Lighting." Included in one comprehensive volume is everything one needs to know about lighting - explanations of concepts, techniques, applications, procedures and systems, as well as detailed definitions, tasks, charts and diagrams. Full color illustrations exemplify important concepts and expert contributions ensure technical accuracy. The 9th edition is new and extremely important to all lighting professionals, particularly the Lighting Design Guide (Chapter 10) which replaces the former illuminance recommendation table and changes the way lighting issues for the next millenium are considered.
https://www.iesna.org/shop/item-detail.cfm?ID=HB-9-00&storeid=1
The are several lighting fixture manufacturers that offer lighting calculation sofware, either at low coat or no cost. Lithonia is one and Cooper is another. One of the fixture reps can assist you.
The wall packs will give a significant amount of glare and would be a poor application for these fixtures if used for anything except general lighting for the patio.
The wall packs will give a significant amount of glare and would be a poor application for these fixtures if used for anything except general lighting for the patio.
cajun62234
Member
As stated; the CU factor of the chosen fixture will also govern the fc levels; but who are we to say what his/her wants are (swimming? volleyball?) and putting MH on his/her deck for outdoor lighting is asking every insect within 100 miles to 'pay a visit' to the outing.
If he/she insists, mount the fixtures at 18' c/c, but they would be better off with HPSodium (24k hour life and less 'visitors'). Of course Low Pressure Sodium is almost insect-proof,[about 540 nanometers] but the CRI would be almost unacceptable. (just like Dad's backdoor, Summer time 'bug light')
If he/she insists, mount the fixtures at 18' c/c, but they would be better off with HPSodium (24k hour life and less 'visitors'). Of course Low Pressure Sodium is almost insect-proof,[about 540 nanometers] but the CRI would be almost unacceptable. (just like Dad's backdoor, Summer time 'bug light')- Status