fluorescent grow lights
 

Did I read somewhere on here that florescent lights lose some of their light power after using for a seed starting season and should be replaced each year? I hate to say that mine are going on their 4th season so if that is true, I better replace this year.
Sue

I am with you. My bulbs have been in place four years at least and seem to give pretty good results. I think I will replace some of the older bulbs this year. Any bulbs that flicker or are noticeably dimmer than the others are gone. Maybe a sticker with the year changed on the fixture will help and then change out the bulbs on a four or five year rotation.

I do remember this topic from a year or so ago somewhere had some pretty specific information on percentage of light reduction after so much time. I am sure one of the light technicians will chime in.

Those of us who grow ornamental plants year round under fluorescent lights (on for 16 hours a day every day) often change out tubes once a year if we want good flowering on light loving species. Technically, after about 8-10 months (how many hours is that?) the output starts to drop steeply, and then the curve flattens out at a lower output for years before they decide to burn out.

For seed starting one month a year new tubes will last forever. When you are trying to get orchids to flower well you need alot more light than when you are just trying for vegetative growth.

I use them approx. 3 months each year so that would be a total of 9 months of use to date.
Sue

Very easy to decide what to do.

1. Get a new tube and put it in.
2. Put it next to your old ones and compare.
3. If you can't see a difference, don't change.
4. If the old ones look dimmer, time to change.

dcarch

Here is a graph. T8 flourescent is the one for most people's
standard 4' flourescent lights (40 watt bulbs, 80 watt fixtures):

[url]http://www.bchydro.com/powersmart/technology_tips/maintenance_guides/lighting/output_declines_with_time.html[/url]

(There is lots of good info on that site.)

Edit:

Should be "T12 flourescent is the one for most people's standard 4'
flourescent lights ..."

[quote=dice;112384]Here is a graph. T8 flourescent is the one for most people's
standard 4' flourescent lights (40 watt bulbs, 80 watt fixtures):

[URL]http://www.bchydro.com/powersmart/technology_tips/maintenance_guides/lighting/output_declines_with_time.html[/URL]

(There is lots of good info on that site.)[/quote]

Good graph.
Also keep in mind that for all lights requiring ballasts, electronic ballasts will make the lights last much longer. (most new flourescent fixtures have E. ballasts).

dcarch

Thanks for posting that, I did not know that the T-8s held their output better than the T-12s. It looks like dirt accumulation has alot to do with declining output too.



I think the T-8s are only 32 watts = more efficient. The older T-12s were 40watts, then dropped to 38 watts. Most of the cheaper shoplights fixtures still use the thicker T-12s unless that has changed in the last two years. (For those of you who don't know, the number represents tube diameter in 1/12 inches, I forget what the "T" stands for.)

Mine are the 1 1/2", 40 watt bulbs. How does one know if they have electronic ballasts? The fixtures are 5-6 years old. Sounds like a good cleaning will brighten them some. Thanks for the graph.
Sue

[quote]I think the T-8s are only 32 watts = more efficient. The older T-12s were 40watts,[/quote]

Correct (I had to go back and take another look at the box).
The 40W bulbs (the style that has been around for many
decades) are T-12s.

[quote=akgardengirl;112397]-----How does one know if they have electronic ballasts? ------Sue[/quote]

Magnetic ballast is bigger and heavier and runs hotter.

Electronic is smaller and on the ballast it will sometimes say electronic.

I would throw away magnetic ballast fixtures and get the new ones. It pays soon enough.

If you are into tinkering. With electronic ballasts you can try "over driving" the lamps for more light output.

dcarch

Unfortunately, not all electronic ballasts are created equal. Couldn't overdrive my Phillips electronic ballasts. Ami

More important than any other factor to get more output from the same light system are the fixture reflector design and the reflectivity of the setup design of your environment.

It can make a 100% difference.

dcarch

Is there an inexpensive way to increase the reflectivity of the reflector of a standard shop light? Silver spray paint?

The side reflectors on the lights I have are very short, they don't extend much beyond the depth of the bulb thus allowing the light to disperse rather than directing it.

Last year I started draping long pieces of aluminum foil over the fixtures to reflect as much light back onto the seedlings. I do enclose the entire seed starting area in silver mylar. Any other suggestions for increasing reflectivity?

Polished aluminum/mylar has a high reflectance (95%), foil does not. Flat white is better than foil (~90% vs ~70%). Foam poster board is easy to cut/work with, and you can buy 4ftx8ft sheets of white sound insulation styrofoam at Lowes/Home Depot that make it easy to make a shoplight sized light box. You want to enclose the area as much as possible so that reflected light bounces around inside rather than escaping out cracks. Rather than try to improve the reflector, simply have the light inside the "box". You can also buy white/black grow room plastic or mylar from hydroponics suppliers online. I think the styrofoam box is easier to work with.