Here Comes The Sun(lamp)

March 5, 2021 4:13 AM

My apartment has so far been...okay for my plants; but I want to get a grow light so the herbs get a boost. I'm just not sure how much of a boost to give them.

I'm on the top floor of my building, and my windows are east- or west-facing and have really deep sills, so I've been doing okay putting them on the windowsills pushed up against the glass. They get about 4-5 hours of direct sunlight a day depending on the season, and then indirect the rest of the day. And they've been fine that way - they stay alive and see to be okay. But they do get a bit leggy, and tend to "reach out" towards the light, so I wanted to get a simple grow light to boost things up a bit.

I'm just not sure how long to use it for. The one I'm looking at has a timer and different level light settings, and that's just confusing things for me; should I turn it on first thing in the morning with the sun and leave it on for 8 hours? Turn it on only partway in the morning and boost it up to full in the afternoon? Wait until the afternoon to turn it on?

I could always just get a simpler lamp, I'm sure, but I like the "automated" element of this, where I won't have to remember to turn it on every day and it'll just do it on its own.

posted by EmpressCallipygos to Home & Garden (11 answers total)

I would use it to supplement the sun based on daylight hours and if they're in an east or west facing window. The east-facing plants likely need a boost after mid-morning, and the west-facing likely need a boost until early afternoon.

I have this one (similarly automated, because back when I worked IN an office I wanted my plants to have weekend light) and would usually give them 12-16 hours of light, but I didn't have any direct light.
posted by DoubleLune at 5:21 AM on March 5, 2021 [1 favorite]

Response by poster: Ooh, I like the timing on that one a little better. Do you know if they make one that isn't on the gooseneck? (I was going to tape mine to the window sash just behind the valance, as the plants are on a tall-ish rack in the sill.)
posted by EmpressCallipygos at 6:37 AM on March 5, 2021

Apparently SAD lamps work on plants too?
posted by ellieBOA at 6:46 AM on March 5, 2021 [1 favorite]

This is one of the few places I’ll use IoT stuff and have some WiFi switches paired with all our grow lights (which are only controlled by It gives a bit more flexibility in providing a planet what what they need. Divorcing the timer from the lamp allows many more lamp options. All of my experience with lamps usually ends up being “need a brighter light” or “needs to be closer to the plant.” There are a ton of grow lights out there that are so wildly insufficient in producing enough light.

And I would suggest if you’re getting into lights and lamps, to invest in even a cheapo light meter. It’ll help you gauge much better how much light each buddy needs.
posted by furnace.heart at 7:16 AM on March 5, 2021

I use this guy with a desk lamp and an IoT timer to control when it turns on and off. Good enough for maybe 2'x2' area. The quality of light it gives out is great to the human eye, compared to those grids of red and blue LED's that work great but are tiring to look at.
posted by Dmenet at 7:39 AM on March 5, 2021

Response by poster: Gentle redirect that I am mainly looking for advice about how much light to use and when, as my primary question.

I'll accept suggestions for "alternate sources of light", like Dmenet gave me above, but my main question is "okay, now that I've got the damn thing, what comes next".
posted by EmpressCallipygos at 8:58 AM on March 5, 2021

How much/when light will depend on the plant; if you’re looking to explore this, a light meter is almost a necessity, otherwise you’re just muddling around without any clear guidance.

houseplant journal Can be a bit, obnoxious, but a a great resource for learning is to measure light and provide enough for a variety of plants.
posted by furnace.heart at 9:13 AM on March 5, 2021

All lamps give off heat and the heat from the sun plus heat from the lamp will be too much for anything but a cactus. Leaves have an upper bound of how much/fast they can convert light to sugars with photosynthesis and going beyond that point just stresses the plant because it tends to lose water through pores on the leaf that have to be open during photosynthesis faster than it can replace through the roots or it gets a burn from excess heat much like human skin, so you want to get right up to that edge of too much light and back off. For herbs like mint and rosemary they will really appreciate max output from your lamp any time the sun is not directly hitting them up to about 12 hours of light a day. Plants have circadian rhythms too and need dark but not more than about 8-10 hours, so you want to turn your light on max in the morning and evening to extend day length up to that point, and any time the sun is directly hitting them turn it off unless it is partly overcast. signs of a "good" amount of light are vigorous, compact, non-leggy new growth and the plant using up the water you give it within a few days assuming it has good drainage. signs of too much light/heat stress are yellowing/bleaching of leaf tips especially near the glass.

so I can't tell if you can actually program this in the particular light you mentioned but it would be for the west facing window- 5 hours of full output from your light from about 7am-12pm or so and maybe max all day in winter if you are far north. For east facing window, from 12pm-6pm continuously at max and maybe turn it to half or 25% output in the morning from 7am-12pm depending on how hot it gets and how the plants respond. put your tougher things like rosemary in the west window, put the things with more delicate leaves like dill in the east window. That lamp is not high wattage so it won't do any good at all unless it is VERY close to the leaves - like 12" away at the very most. Farther away than that and it won't be a usable concentration of light. It doesn't have to be above the plants though; light from the side still counts so play with suspending it on a wire from the valance or mounting to the side of the frame at plant height.
posted by slow graffiti at 9:57 AM on March 5, 2021

also light meters start at several hundred dollars if you want something accurate for plants, not photography, and your phone doesn't count even though there are apps that supposedly tell you. the best guide is watching the plant's response.
posted by slow graffiti at 9:59 AM on March 5, 2021

If you're using LED lighting you're really unlikely to cook your plants at any range over an inch (I've successfully raised seedlings under fluorescent tube lamps an inch above the plant tops, and fluoros throw out roughly twice as much heat as LEDs with similar visible light output). Be a little more conservative if the lighting you're using is a concentrated single source with a reflector than if it's some kind of panel.

Some plants are much more sensitive to day length than others. Depending what you're growing, you might find that playing with day length will let you encourage continuous flowering, or more prolific leaf growth, or shorter stems or something else. Best thing is just plug in your lamps and your timer and keep notes. A day length about the same as that provided by the sun for the season you're in would be a sensible starting place.
posted by flabdablet at 12:24 AM on March 6, 2021

I’ve grown all sorts of seedlings using LED lights, both in a windowless bathroom or on a windowsill. In both cases, I’d turn on the lights when I woke up, and turned them off when I went to bed. Worked fine. Never had any burning issues. I’d spend that same money on an LED light sans timer.
posted by Neekee at 6:58 AM on March 7, 2021