Current Progressive Dairy digital edition

1408 PD: What type of light bulbs do you think are great?

Larry Trissel Published on 29 September 2008

When choosing lighting fixtures for dairies, producers should understand the differences between T-5, T-8 and LED bulbs and fixtures.

Extending the hours of light cows perceive – long-day lighting – makes more milk. There has been much discussion regarding long-day lighting programs for the dairy industry and the most efficient and best rendition of lighting for dairy animals.



“When lactating cows are exposed to 16 to 18 hours of light each day, they produce 5 pounds per day more milk,” says Dr. Geoff Dahl of the University of Florida Department of Animal Sciences. “That translates to over 1,500 pounds more milk over a typical lactation.”

The key is to select the most efficient form of lighting that is appropriate for your facility in order to reduce the cost of implementing long-day lighting.

Lighting companies around the world continue to improve the efficiency of their bulbs. Manufacturers of lighting fixtures continue to streamline their products to direct lumens evenly on the cows’ environment. Strides continue to be made with lighting companies making bulbs more environmentally friendly and more efficient, including the T-5 bulb.

There is no question that T-5 bulbs are 11 percent more efficient than their predecessor, the T-8 bulb. These fixtures are not only are more user-friendly in colder climates, as temperatures drop below 32°F, but also give out more lumen per dollar spent.

An illustration of the efficiency of T-5 bulbs is to compare watts per lumens. For example:


T-5 = 5,200 lumens ÷ 51 watts per bulb = 102 lumens per watts

T-8 = 2,900 lumens ÷ 32 watts per bulb = 90.63 lumens per watts

T-5 bulbs also start and operate at full bright in temperatures -22°F to 190°F. Fewer fixtures are needed to attain the same lumens as provided by other fixtures.

In addition, power companies across the U.S. are offering rebates to replace old fixtures with new energy-efficient fixtures. In most cases, larger rebates are offered on T-5 fixtures. Are T-8 fixtures more efficient than the older models? Sure. But there is a reason the rebates are larger for T-5’s.

There has been hearsay that T-5 ballasts overheat, causing them to fail. This is a myth. Dairymen can attest to the contrary. Many dairymen in the Midwest have been using T-5 fixtures for years with less than 1 percent failure rate. In the lighting industry, this is more than acceptable.

A word of caution for dairymen installing lighting would be to factor in dirt and fly specs accumulating over time on the fixture lens. Unless planning to routinely power-wash your fixtures, it would be advisable to incorporate a couple of extra foot candles into your lighting budget. If power-washing, make sure your fixtures are Underwriters Laboratories (UL) approved with an IP-65-IP-67 rating for final assembly. (If the rating is not for final assembly, the fixture installation is restricted and cannot be mounted against flammable material. Insurance companies frown on fixtures not manufactured with a UL final assembly rating. Check the rating online with the UL number from inside your fixture.)


There is increasing chatter concerning the newest generation of bulbs on the market, the LED. Many flashlights and some city lights have converted to this alternative. The life of the bulbs is exceptional. However, the spread of light over the area being covered doesn’t come close to emitting 20 or more foot-candles.

At this time, we are not aware of any LED capable of exceeding the equivalent of a 75-watt incandescent bulb. The limitation is a result of overheating problems with circuitry. Until this problem is resolved, the LED should not be considered for this type of dairy application. PD

Larry Trissel
Ag Solutions Plus Inc.