What can I grow under a T5 Hydrofarm 4' x 4 bulb light fixture?

[naoki]

My measurement is pretty similar. But I think they are lower than rosemadder's because it is 2' bulbs. I now use 4' unit, but I haven't measured it yet.

I grow mostly species paphs, and the distance between the bulb and the top of the leaves are around 9-10" (or less for tall ones). The plants are getting about 1000 fc. But you might need to gradually increase the intensity. Last summer, some species did get heat stressed (I grow them in a grow tent, so heat is a problem even in Alaska).

I was using 15hours day (no seasonal change), but trying to reduce the day length, and it's now 14h/day (it costs me >$300/year for electricity, so I'm trying if they will grow ok with shorter day length).

Fixture: Hydrofarm FLT24 2-foot 4-bulb (pretty decent reflector)
Bulb: Hydrofarm AgroBrite 24W 6400K T5 HO, about 4 month old, with 15hr/day
Light meter: Gossen Ultra Pro (pretty high-end).

I made the measurements in the middle of the bulb (the brightest point).

With 4 bulbs:
595 fc @ 1 foot from the bulb
1165 fc @ 6 inches from the bulb

With 1 bulb:
205 fc @ 1 foot
595 fc @ 6 inches

As you probably know, lumen/W is slightly lower with 2' bulbs than 4' bulbs.

4': 5000lm/54W = 92.6lm/W
e.g. GE bulb: General Electric: 48" T5 6500K High Output Starcoat, case of 10

2': 2000-2100lm/24W = 83.3-87.5lm/W
e.g. GE bulb is 2000lm: General Electric: 24" T5 6500K High Output Starcoat

[jeremyinsf]

I guess a light meter needs to be the next thing on the list to buy!

[rosemadder]

In the meantime though, you can probably use our numbers as an estimate to go by. Very similar lights to yours.

Artificial light is a little funky though. It may count for less depending on the actual spectrum of the bulb, or it may count for more since artificial lights are so steady for long periods while natural light is not.

I have a couple of old 54-watt 6500k compact fluorescents that I put over my windowsill orchids. At the leaves, the extra light is only about 600fc, but my vandas have noticeably perked up. No idea yet if they'll ever bloom, of course.

[DTEguy]

Try searching for free phone apps "light meter", lux meter"....they are pretty good and saves you money for more orchids

Originally Posted by jeremyinsf

I guess a light meter needs to be the next thing on the list to buy!

[jeremyinsf]

Thanks Yang, I saw some other stuff about them after I posted that and downloaded a couple of them. The readings seem high and as I understand it, different phones might need to be adjusted due to how their sensor works. So I'm going to try to borrow a 'real' meter and calibrate my phone, and then be good to go.

Thanks for the suggestion!!!

Jeremy

[naoki]

Jeremey, aren't these apps "reflected" light meter instead of "incident" light meter?

[DTEguy]

Originally Posted by rosemadder

the extra light is only about 600fc, but my vandas have noticeably perked up.

I understand that different bulbs may vary, but from my limited experience with my T5's PAR, about 30% of the reported footcandle is all I needed--under my 14 hours light exposure.

So, the 600fc that you provided "could" be equivalent to a 2000 fc (at peak) sunlight.

[jeremyinsf]

Originally Posted by naoki

Jeremey, aren't these apps "reflected" light meter instead of "incident" light meter?

Yes, and that's why the different camera's light sensors report things differently.

If you use a "real" light meter you can do the internal math in your head to see how far it's off.

Or some of the apps let you actually calibrate it. One of them I have has some pre-sets but my phone isn't listed as one of the devices that has a pre-set.

[bballr4567]

Just an update here. My Onc. Sherry Baby has 5 spikes from 3 new pbulbs. All from under lights.

[rosemadder]

Originally Posted by DTEguy

I understand that different bulbs may vary, but from my limited experience with my T5's PAR, about 30% of the reported footcandle is all I needed--under my 14 hours light exposure.

So, the 600fc that you provided "could" be equivalent to a 2000 fc (at peak) sunlight.

Ooh! Highly intriguing! Do you know of any good sites that explain a bit more about that sort of thing? If I recall correctly, PAR meters are rather pricey, so I may not be able to get one for a long while yet, but I'd like to research this in the meantime.