Trying to figure how many lights t5 HO 4 bulbs to use in a 60 x 80 x 18 open area shop with 3 bays working on large equipment (Or a better light option if one available, trying to stay green and economical as possible.) How many lights to put on a circuit? THANKS

Hi

First of all you need to determine how much light you want, measured in footcandles. Then you need to determine the lumen output of each fixture. Only then can you calculate how many lights you would need for the desired footcandles. And this should depend on exactly what you expect to be doing in this shop. Very often supplemental task lighting is a better option rather than trying to raise the footcandles of the total area.

See attached information how to do a simple RCR ( Room Cavity Ratio) calculation, and you will see that even this is not that simple.

Since you mention 3 bay and large equipment, I will assume this is a commercial garage that will contain large trucks, earthmoving equipment, or something of that nature.

If this is the case, any lighting calcs will assume an even spacing of fixtures, and a truck garage will not want fixtures evenly spaced. Fixtures will not be needed directly above the equipment, however, placed on both sides and in front, and perhaps at the rear of the equipment, if possible or necessary.

Before any calcs are done, the exact details of the fixtures and lamps is needed.

I can tell you that a Phillips 54 Watt T5 lamp at 4100 Kelvin has a design lumen of 4750 lumens. Any other lamp manufacturer or color temp may have a different design lumen amount.

So along with knowing the exact lamp, the exact fixture specifications is needed. For example, fixtures with white reflectors will have a different efficacy than one with a silver mirror reflector. One with uplight slots will be different than no uplight slots.

To illustrate the complexity of lighting calculations I offer this:

http://pelmatp.doe.gov.ph/images/Module%204V%20-%20Lighting_Calculations.pdf

If your purchasing fixtures from a lighting distributor, they will have software to help layout the lighting to suit your needs. If your getting your fixtures from a large box hardware store, then I understand why you're here, as they will be useless in helping layout lighting.

Minimum light level for a service garage is 100 footcandles at task level. Someone needs to determine what task level is, at the floor, at 30 inches above floor etc.

This was Missouri's point, while your task may be inside a engine compartment, getting 100 foot candle from ceiling lighting may not be practical, and that general lighting will usually suffice, and then use drop lights for the close up work.

If you get back with more detail, perhaps we can help. We do know the length, width, and height of the space, Need to know the color or type of walls, ceiling, and floor surfaces, make and model number of fixtures and lamps, type of task to be performed..

Only after the amount of fixtures is determined, can the branch circuit wiring be calculated.

We are do it your selfers. Mom and pop operation. Finally able to put up a building to hold and work on our equipment. You are correct in your assumptions of the trucks and large equipment. The ceiling and wall areas are painted white steel sheeting. The floor is concrete light grey. The task level varies from 2' to 5' on average depending on equipment. Have not picked a brand of light yet as I am still researching my options other than the fact that they will be T5HO lights. Any help in that area will be appreciated as it gets confusing as as there are so many options. Have looked at the StoncoPhilips TBN454EB1-8 T5HO Highbay 4 lamp fixtures from Pro Lighting but not sure of the bulbs that we should use . Also have checked out the Ultralux ULHBT5-446 w blue max bulbs 5900 K but not sure about recouping the extra cost.
Thanks for your input.

See attached lighting plan, using the Stonco fixture you mentioned.

This plan shows a symmetrical layout, and does not allow for trucks.

You could install these lights exactly per plan, and you would be pleased.

I assumed that task level is 30 inches above floor.

I submitted my last post a bit quick. While the fixture layout I provided will be more than adequate, it can be scaled down some. Fixtures can be moved so fixtures are not wasted over any large equipment.

Less fixtures will reduce the average 100 footcandles, but lighting will still be adequate.

Light stands or drop lights will be needed anyway, so less fixtures may still work out for you.

Once you determine the total fixtures, then the wring can be designed. As you can see, each fixture draws 233 watts. If your using 120 volts, one 20 amp circuit can handle no more that 1920 watts, and you can have 8 fixtures per one 20 amp circuit.

No response?

Did I answer your question?

Any comment on the lighting plan I prepared for you?

Feedback is always appreciated.