Light levels and/or replacing an old bulb?

[Syrinth]

So I finally go off my butt and got a light meter and thermometer so I could get a better idea of my growing conditions. Apparently my plants were suffering from heat stroke this summer which is why started to defoliate.

I was checking my light levels and, according to the light reader, my grow lamp is only getting maybe 100 footcandles to the leaves of my orchids about a foot and a half away from them. Despite this, the orchids seem fine.

I'm using a Sun Blaster CFL 200W 6400K light bulb and, as I've said, I've had it for about two years now.

Under that light I have a psychopsis and a cattleya that both grow and bloom, as well as a NOID Oncidium, two paphs which have previously bloomed and a dend. miva abracadabra.

Since I've had the bulb for a bit, maybe it should be replaced, but I'm confused about how, if the meter is accurate, the orchids are still growing/alive with that little amount of light?

[PaphMadMan]

Some artificial light does not have full spectrum wavelengths, and light meters are completely inaccurate in determining how bright they are, at least in terms of useful light for plants. Yours should be full spectrum though, so the meter should be reasonably accurate. What does the meter read in direct sunlight?

If the plants you have are growing well and blooming regularly, that tells you they are getting the light they need. That is more important than a reading on a meter. CFLs should be replaced periodically, though, and after 2 years there has certainly been some decrease in output.

[Syrinth]

In the morning in my south facing window, the meter was reading around 500 fcs I think.

[Ray]

You sure you're not missing a scale multiplier on the meter? Even at 2 years old, from 18", the plants are obviously getting more than 100 fc.

[Syrinth]

That's what I was thinking as well, but there are X1, X10 and X100 scaling knobs. The X1 puts it at about 100 FC, and if I put it to X10 then it just drops almost all the way down.

[Leafmite]

It is recommended to change the bulbs after two years. This will be my third year of growing under lights and I replaced the bulbs of my Hydrofarm and Sun Blaze lights to be ready for when the plants come inside. The one light fixture still has another year as it was not used last year so...next year.