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How to calculat the area covered by light?

  1. Mar 28, 2010 #1
    Dear engineers,

    I need to know how to calculat the area of the light that covered by flood light with 400W and supplied with voltage rated at 220-127V current I=20A.

    for the informatoin that flood light will be fixed on the 10M height pole directed to the company logo on cooling tower to make it viseble clearly at night
  2. jcsd
  3. Mar 28, 2010 #2


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    To get an answer to this you need to specify how big the sign is, what sort of floodlight you are using and how visible you actually want the sign to be - i.e. a figure for the actual required illumination level. Is the sign out on its own in the desert or is it amongst a load of other light sources, for instance?

    I think that you have the best chance of finding out some sort of answer to your query by driving around at night and looking at similar signs which you would consider to be adequately lit. Then ask the owner what lights he is using. Flood lights are all fairly standard - 400W, 1kW etc. with very similar patterns (up to about 90 degree beams) so you can't go far wrong this way.
  4. Mar 28, 2010 #3
    There is software to simulate lighting installations that is free, It is called Dialux. Generally you need to pick a fitting and get the photometry file which is essentially a polar plot of luminous intensity.

    You may be able to palm the calculation part of the problem off onto a lighting supplier. I'm not sure who are common suppliers in you area.
  5. Mar 29, 2010 #4
    thank you engineers. however the logo dimensions are 30MX30M and at the 10M height, I proposed for 3 poles suitable for mounting on foundation with two floodlights. the power suorce will be taken from the nearest sub station lighting panel rated at 220/127V, 3ph, 4W, 60Hz, and one circuit breaker with 20A will be used to protect these flood lights. on the other hand, the cost of this project was high where my superviser comments on the propsel to reduce the cost by proposing one pole with 2 flood light. in my Opinion this will not work since the logo is big. So, I need to calculat the area of these flood light to be sure if it will work or not. whereas, if it is not so no need to wast a money for a non necessary installation
  6. Mar 29, 2010 #5


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    You'll have to point out to your supervisor that sad, inadequate, lighting will not be a good advert! If all you get is one little pool of light in the middle of that huge sign, it won't impress anyone. The last thing you want is to turn on a poor system and open yourselves to 'public humiliation'!
    I have done some stage lighting and have found that the kW quickly get eaten up when you want to get a good, even, illumination. Ordinary 'security' floods are at least 500W but are a bit wasteful if you need a specific item illuminated.
    I agree that you really need something like your original proposal. I have no idea what your logo cost but it can't have been cheap. The lighting installation wouldn't be too much in comparison. It seems that your substation could give you 4kW and, at 0.5kW for each luminaire, you could handle up to 8. The power cost 4kWhr every hour, could hurt a bit over a whole year of 12 hour nights, average.
    There is also the issue of how far away the floods will be, so that you can decide on the angle of the beams you need. The further away you are, the less variation you will get in distance / spread from top to bottom. So called 'vignetting' could spoil an otherwise nice sign so you will need to 'spill' quite a lot of light at the edges.
  7. Mar 29, 2010 #6
    I work as a electrical engineer in building services where lighting design is a primary part of my job. Sophiecentaur is correct, a poorly illuminated sign will be noticeably bad.

    I stand by my suggestion above, find a local lighting supplier (commercial not residential) and get some advice from them. They will have the design knowledge you require and possibly some statutory requirements that may apply such as spill light limits.

    I work in australia, but I think in america Ruud lighting, Sylvania, GE or phillips would be reasonable starting points.
  8. Mar 30, 2010 #7
    thenk you very much engineers for your discussion it was useful
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