new fan/vent lets a little light in . is this a problem

hi
I have a 4" inline fan at the top of my grow exhausting the air out. I recently added a small 4" bathroom exhaust fan to the bottom of the grow, this lets the light from the room pass into the bottom of the grow. just a little light gets in.

is this a major problem for the dark period, will it screw my grow up. or is a little light ok ?(I know sounds dumb even as i type it, but if you dont know , ASK).

does anyone have any ideas on how to block the light coming through the fan. I only have to worry about this when the light is off, the fan is off when the light goes off.

I was thinking a piece of card attached to the top of the ducting that would blow up when the fan was on, letting the air in and settle back down and block the light when the fan went off for the dark period.

I am open to other ideas..

thanx in advance

Ectomorph , hippy farming

Just go to a HVAC supply house or heating n plumbing in your area and ask for a 4 inch back draft damper, this is what you are talking about attaching a card (back drart damper)

Put an elbow on it, light only travels in a straight line.

Thnx Jrainman .. will get on that one.

If i cant find what Im looking for, will try the 90 degree bend DeeTee, I have some spare 4" flexi ducting..

quick and to the point helpful solutions. thanks again..

Ectomorph , Hippy Farming

The flexi ducting doesn't work well unless you make a whole lot of a curves and corners, at least not with the translucent plastic or the reflective foil ducting.

I like your idea to make a lid on it that opens when the fan is on, I could have used that for my active intake which is also only on during light on period. Something like an opaque light weight piece of cloth might work easier as the lid. Instead I built small box / housing outside my grow closet and on the inside,with offset holes.

Im also liking the opaque cloth idea .. maybe just a small length of metal wire , running along the bottom of it.

great minds and all that..

thnx again,

Hippy Farming