Lumen Method help!

[fadox21]

Hi guys currently doing a hnc and I am stuck on a question regarding the lumen method of lighting design. Ill post the question underneath-

A workshop is 40mx50m to be illuminated with 1000w high pressure mercury vapour lumnaires providing an illuminance at working level of 283 lux. The lamps have an efficasy of 59lm/w with a utilisation factor of 0.6 and a lighting loss of 0.8.

If the space to height ration is 1.25:1 determine the mounting height?


Now the problem am having is every formula to work this out I can find needs to know the working plane height, which I do not have. I know its in there somewhere. Myself I think the working level lux of 283 needs to be transposed to find out how they got that which should then give me my working plane height. My head is baffled now lost all my will (tissue) ha. Any one who could help would now be classed as my new best freind haha! I know one of you clever chaps know this straight away so any help would be great! Thanks

 

[hermetic]

IESNA Lighting Handbook.pdf - 4shared.com - document sharing - download
Lumen method - Wikipedia, the free encyclopedia
Hope this will help you. I used to do this in lumens per square foot with various allowances for what was going on in the building, but that was back in the day.
Phil.

 

[fadox21]

Thanks for the reply I have checked wikipedia but have been looking for the lighting handbook so will now follow that lead. Again thanks for your help

 

[catazia]

Hi, this might help you

F = (E A)/(cu mf)

F=total luminous flux (lumens)
E=illuminance (lux)
A=area (m sq)
Cu=coefficient of utilisation (decor)
Mf=maintenance factor (dirt/dust)

so: F= (283x40x50)/(0.6x0.8) = 1179167 lumens required.

and: 1179167 lumens / 59 lumens per watt = 19986watts worth of lighting required.

therefore: 19986w / 1000 watt lamps = 19.98 lamps required (20 lamps)

Now you need to arrange the 20 lamps inside the 50m x 40m area. If you think about it, 4 rows of 5 lamps equals 20 lamps and fits perfectly in the area. Remember that the spacing around the edges of the area should be half the distance between adjacent lamps. If you draw it out and write the distances between each adjacent lamp (remembering it is half the distance around the edges) you get a nice round number for the 'spacing' between lamps.

Working out the height of the lamps is dead easy now because we now know the 'spacing' distance in metres.
As the 'spacing/height ratio' is given as 1.25:1 , simply divide the 'spacing' distance by 1.25 to get the height the lamps need to be.

I made it exactly 8 metres.

(ps. it took a lot longer to type all this than it did to do the sum!)