Daylight, glare and darkness: keeping the light you want and stopping the rest
Sheer, light filtering, room darkening and blackout describe how much light a fabric stops, not how dark a room gets. This chapter matches an opacity to each window, traces glare to its source, and closes the gaps at the edges where darkness matters.
- Start here: the essentials
- Light at the window, hour by hour
- The four opacity words
- Tracing glare to its window
- Solar shades: openness and color
- Darkness for sleep, and the edges
- Reading a shade spec sheet, and the studies in full
- See it
- Practice
- Your windows
- Check your work
- Knowledge check and scenario
Start here Essentials
At minimum, this chapter asks you to say when each window's light is wanted and when it is a problem, then give each window an opacity and, for a bedroom, a plan for the edges. Everything marked Go deeper is optional on a first pass.
- Write when the light is wanted and when it is a problem. Morning, midday, afternoon and the hours someone sleeps (Light at the window, hour by hour).
- Find the window behind any glare, at the hour it happens. Sit where the problem is and look back toward the light (Tracing glare to its window).
- Choose an opacity for each window from the four words. Sheer, light filtering, room darkening or blackout, and write what it will not stop (The four opacity words).
- Where darkness matters, plan how the edges will be covered. Light comes round the sides and top of even an opaque fabric (Darkness for sleep, and the edges).
Minimum time: about 30 minutes for one window, plus a few minutes at the hour the light is a problem. Done when: each window on the survey has an opacity and, for a bedroom, an edge plan.
1. Light at the window, hour by hour Understand
A window treatment does two opposite jobs with light: it lets in the light you want and stops the rest. Which is which changes through the day. The same east window that wakes a bedroom at six can be the one you want open at nine. So the first step is a record of time, not a choice of product.
What sunlight is made of
Sunlight reaching the ground is roughly 44 percent visible light, 53 percent infrared and 3 percent ultraviolet, according to a window film trade association's Advanced Solar Control Education Guide 2026, which notes that other references give slightly different shares. Physical principle The split matters because each part does a different thing in a room. Visible light is what you see by and what causes glare. Infrared is felt as heat. Ultraviolet is a small share by energy, and it fades and weakens fabric, which is the subject of Fabric, linings and fading. A covering can be good at one and poor at another: a pale shade can reflect heat well and still let a lot of diffuse light through, as the solar shade figures below show.
Direction decides the hours
Which way a window faces sets when the sun reaches it. A University of Oregon daylighting lecture slide on window orientation (undated) puts the pattern plainly: north and south windows are easy to protect from sun while still admitting daylight, and east and west windows face the low rising or setting sun, which brings severe glare and overheating. Physical principle The same film association's guide adds the seasons for the Northern Hemisphere: summer exposure is highest on east and west windows, winter exposure highest on south windows. Physical principle
Those are general patterns. A tree, the building across the street, a porch roof or deep eaves change them for your window, and only looking at it settles it. What each window needs covers finding north and the window across the seasons. For this chapter, what you need is a short note per window of when direct sun or bright sky actually reaches the glass.
Wanted, unwanted, and when
For each window, write four short lines: the light you want and when, the light that is a problem and when, whether anyone sleeps in the room in daylight, and whether a screen or a seat faces or backs onto the window. The What each window needs sheet has columns for the light wanted, darkness needed and glare, so the note goes straight into the survey.
| Window faces | Direct sun, in the general pattern | Usual problem | Usual want |
|---|---|---|---|
| East | Morning, low and level | Early waking in a bedroom; glare on a screen in the morning; summer heat | Morning light in a kitchen or office, once the sun is higher |
| South | Midday, higher in summer and lower in winter | Winter sun low enough to reach under eaves and across a room | Winter daylight and warmth |
| West | Afternoon and evening, low and level | Glare on a television or screen late in the day; summer heat | Evening light in a living room |
| North | Little direct sun in the Northern Hemisphere | Seldom glare; privacy and cold matter more | Even daylight all day |
The table restates the University of Oregon slide and the film association's seasonal pattern. Your own window, observed, overrides it.
The aim of the record is to find conflicts. A window with no conflict needs whatever its other needs call for. A window where the light is wanted at one hour and is a problem at another needs a covering that can be set two ways: open and closed, a sheer and a lined layer, or a shade that lowers from the top. Writing the hours down is how you see which kind of window you have.
2. The four opacity words
Four words do most of the work on product pages: sheer, light filtering, room darkening and blackout. They describe the fabric or the material, roughly from most to least light passing through. They do not describe the room, because a room's darkness also depends on what happens at the edges, which Darkness for sleep, and the edges covers.
| Word | What it means on a label | What it does | What it does not do |
|---|---|---|---|
| Sheer | A thin, open fabric you can see light and shapes through | Softens light and gives some daytime privacy when outside is brighter | Gives no privacy at night with lamps on; does not darken |
| Light filtering | A fabric that lets light through diffused, without a clear view | Keeps a room bright and evens out light; daytime privacy | Does not darken a room for sleep; can show a silhouette at night |
| Room darkening | A fabric or liner that blocks most light; the maker's own word, with no agreed figure | Darkens a room considerably; gives privacy at night | Does not remove all light, and the edges still leak |
| Blackout | The most light-blocking material a maker sells; one lining maker defines it as blocking 99 percent or more of natural light | Stops light through the material itself, as nearly as fabric does | Does not make the room dark on its own: light comes round the sides, top and bottom |
Sheer and light filtering are the bright end. They keep daylight and give privacy only while outside is brighter than inside; Privacy by day and by night explains why that reverses after dark. Physical principle
Room darkening is a maker's word, not a standard. Hunter Douglas, on its light control and privacy page, says its opaque fabrics darken but do not entirely eliminate light in a room, and offers room-darkening liners attached to the shade or operated separately. It gives no percentage. Product-specific
Blackout is the one word with a published number, and only from one maker. Eastern Accents, a custom drapery maker, defines its blackout lining in its Drapery Lining FAQs as blocking 99 percent or more of natural light. Product-specific That is a figure for one maker's lining material. It is not a definition other makers have agreed to, and it says nothing about what reaches the room past the edges.
Choosing one
Work from the first need you ranked for the window:
- Daylight without glare, and no one sleeps there by day: light filtering, or a solar shade (Solar shades: openness and color).
- Privacy by day only: sheer or light filtering.
- Privacy at night: room darkening or blackout, or a lined curtain, for the hours the lamps are on.
- Darkness for sleep, especially by day: blackout, with the edges planned.
- Two needs at different hours: two layers (a light-filtering shade under a lined curtain, or a sheer under a blackout panel), or a double shade that carries both. Hunter Douglas sells one that pairs a sheer or light-filtering front with a room-darkening back panel. Product-specific
When the word on a product is not one of the four, ask the seller which of the four it is nearest, or hold a sample to the window at the hour that matters. A sample tells you more than a label: hold it against the glass in full sun and look at how bright it glows from inside. Test it
Why there is no percentage for room darkening. We looked for a maker or standards body that gives a figure separating room darkening from blackout and did not find one. Hunter Douglas uses both words without numbers. The only published figure is Eastern Accents' 99 percent or more, for blackout lining. Retail pages repeat figures for both words, but none we found traced them to a maker's definition or a test, so we do not repeat them. When a product page gives a percentage, read it as that seller's claim about that product, and ask what was measured.
Linings change the word. A light-filtering face fabric becomes room darkening or blackout once a lining of that kind is sewn or clipped behind it. The kinds of lining, and what each does for darkness, heat and wear, are in Linings: what each layer does.
3. Tracing glare to its window
Glare is light in your field of view so much brighter than what your eyes are adjusted to that it makes seeing uncomfortable or harder: a bright window behind a screen, the sun reflected off a monitor or a television, a patch of low sun across a desk. It is a problem of one seat or one screen at one hour, so it is traced from there.
Find the window behind it
- Be there at the hour. Sit in the seat, or stand where the screen is watched, when the glare happens. Write the time.
- Look for the source, not the symptom. If the screen shows a bright patch, look at what it reflects: turn your head toward the patch's mirror position, behind and to the side of you. If the light is in your eyes, it is in front of you.
- Name the window, and the part of it. Often it is the top of a tall window, a door's glass panel or a side window, not the obvious one.
- Write it on the survey. The glare column of the needs sheet takes "8 to 10 a.m., office, left monitor, from the east window" in one line.
Low sun and the seasons
The sun's height changes the answer. A window film trade association article, Don't Let The Winter Sun Catch You Off Guard, makes the point that in winter the lower sun can bring more direct sunlight into a building below eaves, and that low winter sun causes glare on computer screens. Physical principle So a seat that is fine in July can have glare in December, and the record from one day is a start, not an answer. East and west windows face low sun all year at the start and end of the day, as the Oregon slide puts it.
Covering the window is one answer, moving the screen is another
Glare has two ends, and it is worth trying the free one first. A screen turned so the window sits to its side, rather than behind it or behind you, may need nothing at the window. Test it Lamps matter too: Layers, fixtures and glare in Learn Interior Lighting covers glare from the room's own lighting and how layers of light reduce contrast.
When the window has to be covered, glare asks for something different from darkness. You usually want to keep daylight and some view, and cut the brightness of the sky or the sun. That points to a light-filtering shade, a solar shade, or blinds with slats tilted, rather than blackout. A film association's guide suggests, for home glare from film, a medium light transmission, a neutral color and low reflectivity, and notes that rooms often receive more light than the people in them need. Product-specific
Rosa and Dev's home office. Known: the office faces east; morning sun puts glare on both monitors from 8 to 10 a.m.; their association's rules (fictional) require coverings that show white or off-white from the street. Sitting at the desk at 8:30, Dev sees the bright patch on the left monitor mirror the window behind his left shoulder. Turning the desk would put the window beside the monitors, but the room is too narrow. They need a covering that cuts the sun for two hours and lets them see out the rest of the day. Assumed: that a shade whose street face is white or off-white meets the rule (their assumption, not yet confirmed). Open: whether decorative film counts as a window covering under their rules, and whether a solar shade's outer color meets the rule; both are settled by asking the association's manager in writing. The color question matters more than it looks: Solar shades: openness and color shows that the pale face reflects heat and cuts view, and a dark face does the opposite.
4. Solar shades: openness and color
A solar shade is a roller shade made of an open-weave screen fabric, often a coated fiberglass or polyester yarn, that cuts brightness and heat while keeping some view out. Two numbers and one choice describe it.
Openness factor is the share of the fabric that is open space between the yarns, given as a percentage. A shade maker's blog post, Draper's What Affects View-Through? (April 2022), defines it that way and gives a typical range of 1 percent to around 13 percent. Lutron's Commercial Roller Shade Selection Guide describes it as the percentage of direct light that passes through the fabric, set mainly by how tight the weave is. Convention A 3 percent fabric is tighter than a 10 percent one.
Visible transmittance is the share of visible light that passes through, counting light that passes through the yarns themselves as well as the gaps between them. Lutron's guide notes that a lower visible transmittance means more glare reduction. Convention It is the better guide to brightness, and it depends heavily on color.
Color changes more than openness does
One maker's specification sheet shows it with one weave in two colors. Hunter Douglas Architectural's SheerWeave 2703 specification sheet lists a 3 percent openness fabric:
| Same 3 percent weave | Visible light through | Solar energy through | Solar energy reflected | Solar energy absorbed |
|---|---|---|---|---|
| Light color (Oyster) | 19% | 22% | 62% | 16% |
| Dark room-side face (Oyster/Charcoal) | 8% | 7% | 40% | 53% |
Source: Hunter Douglas Architectural, SheerWeave 2703 specification sheet. Product-specific One product; other fabrics differ.
Read across the rows. The pale fabric sends back much more of the sun's energy, so less heat builds up at the window, and it also lets through more than twice the visible light, because a pale yarn glows when the sun hits it. The dark face lets through less light and absorbs much more of the energy.
View works the other way from what most people expect. Draper's post explains that lighter colors reflect light, which gives more privacy and reduces view-through, while darker colors absorb light, so the eye looks past the fabric to the brighter outside. Hunter Douglas Architectural's View Through Simulation Tool says the same. Physical principle Draper adds that on a cloudy day or in the evening the eye focuses on the room's light, and the view through the fabric is less clear.
So the default for a solar shade is this: pick the openness for how much sun you want to cut, then pick the color for what matters more at that window, heat reflected (pale) or view and less glow (dark). Your maker's spec sheet wins over any general rule, because the figures change with every fabric.
One more limit, about where a shade suits a window. Retail pages often say that a given openness suits a given direction, such as 1 percent for west windows. We found no primary source that pairs an openness with a window direction for homes, so this manual does not give one. Ask the authority What decides it is the hour of the problem and how much view you want to keep, which you have on the survey.
A smaller openness can still give more glare. Lutron's Performance Fabric Research white paper (April 2015), reporting research with Purdue University, found that fabrics with the same openness but different colors, and the reverse, gave very different visible transmittance and glare results, and that a fabric with a smaller openness factor could still give higher glare. Its view-clarity ranking, from 6,912 data points in full-scale test offices, put dark fabrics with higher openness first and light fabrics with low openness last. These are office studies, with large windows and shades closed, not homes. They support the mechanism above: color and visible transmittance matter as much as openness.
5. Darkness for sleep, and the edges
Darkness is the need where the opacity word matters least and the edges matter most. A blackout fabric stops nearly all the light that hits it, and a bright line still shows down each side of the window.
What the guidance says
The clearest published guidance on a dark bedroom is written for people who sleep by day. NIOSH, the federal occupational safety institute, publishes training for nurses on shift work (last reviewed March 31, 2020). Its page on coping with night and evening shifts says to make the sleep space so dark you cannot see your hand in front of your eyes, or to wear an eye mask; to block light at the bedroom and bathroom windows and on the path between; to use blackout shades or drapes, or both; to block light under doors; and to use a dim red nightlight. Its page on a good sleep environment says the bedroom should be very dark whether you sleep by night or by day, suggests room-darkening shades or heavy, lined draperies, notes that blinds can let too much light filter in, and says to adjust coverings to block light around the edges. It adds that an eye mask works only if it stays on for the whole sleep. A third page, on avoiding light, says "A very dark bedroom facilitates sleep." Ask the authority
For people who sleep at night, the American Academy of Sleep Medicine's Healthy Sleep Habits (updated August 2020) advises limiting bright light in the evening and turning off electronics at least 30 minutes before bed. It does not mention window coverings.
Two laboratory studies are often cited in this area, and we describe them only as what they are. In one, 20 healthy young adults slept one night under overhead room light of 100 lux, and their next-morning insulin resistance was higher than in a group that slept in dim light (Mason and others, PNAS, 2022). In the other, an hour of bright light before bedtime suppressed melatonin in 10 children aged 3 to 5 (Akacem and others, Physiological Reports, 2018). Both are small laboratory studies. Their methods and limits are under Go deeper below.
This chapter teaches what window coverings do to light. It does not diagnose or treat a sleep problem, and it does not say what a darker room will do for your sleep or health. The studies above describe what happened to a small group in a laboratory. If you have trouble sleeping, talk to a doctor. The NIOSH pages are guidance for shift workers on the sleep environment, and we cite them for what a dark room means in practice: dark enough not to see your hand, with the edges blocked.
Where the light comes in
A light gap is the strip of uncovered glass, or open space, between the edge of a covering and the frame or wall. Nearly every covering has some, and they are where most light reaches a room with a blackout fabric.
- Sides of an inside-mount shade. A shade fitted inside the frame is made slightly narrower than the opening so it can move. Levolor's cellular shade technical guide (2022) gives a 3/16 in light gap each side for its inside-mount shades. Product-specific Other makers' figures differ; check yours.
- Top. Over a headrail or rod, and between a curtain's top and the wall.
- Bottom. Under a shade that stops short of the sill, or a curtain that stops short of the floor.
- Between slats. Blinds leak at every slat and at the cord holes, which is why NIOSH notes that blinds can let too much light filter in.
- Between two curtain panels, where they meet in the middle.
Closing the gaps
There are four ways, and the window, the mount and whether you may make holes decide which you can use. Hunter Douglas lists side panels or drapery to cover light gaps, and U-shaped side channels for one of its shades. Product-specific
| Way | How it works | Needs |
|---|---|---|
| Outside mount, overlapping the frame | The shade is wider and taller than the opening, so its edges sit over the trim or wall. Levolor's guide asks for at least 1 1/2 in of overlap each side for an outside mount. | Brackets on the trim or wall above; holes, or a no-drill bracket the landlord accepts |
| Side channels | Tracks at each side of an inside-mount shade that the fabric edge runs in | A maker that sells them for that shade; enough frame depth |
| Curtains past the frame | Lined or blackout panels on a rod wider than the window, meeting in the middle, long enough to pass the sill or reach the floor | A rod above and beyond the frame; see Measuring for curtains |
| A shade under curtains | The shade does the darkness; the curtains cover its edges | Both mounts, and enough projection for two layers |
Two small details close a lot of light. A return, the end of a curtain wrapped back from the front of the rod to the wall, closes the gap at each side. Panels that overlap where they meet close the center. Both are measured in Measuring for curtains, and the light-gap details for each mount are in Measuring for blinds and shades.
An edge plan is one line per bedroom window: the opacity, the mount, and what covers each edge. "Blackout roller, outside mount 1 1/2 in past the trim each side, lined curtains over it" is an edge plan. "Blackout shade" is not, because it leaves the edges unsaid.
Go deeper 6. Reading a shade spec sheet, and the studies in full
Reading a spec sheet
A fabric specification sheet for a solar or roller shade usually gives the openness factor, visible transmittance and three solar figures: transmittance, reflectance and absorptance. Lutron's selection guide states that the three solar figures add up to 100 percent for each fabric, which is a useful check on any sheet: what is not let through or sent back is absorbed and warms the fabric. Physical principle The SheerWeave sheet's light color adds to 22 plus 62 plus 16, which is 100.
Read a sheet in this order. First, the visible transmittance, for brightness and glare. Second, the solar reflectance, for heat sent back out. Third, the openness, for view. Fourth, any UV figure: the SheerWeave sheet gives a UV blockage of 97 percent for that fabric. Fifth, the fire test listed, which is usually a commercial test. The Labels and spec sheets page sets these out with what each number covers.
The film association's guide adds one caution for any window product: spec-sheet values are measured with the sun perpendicular to the glass. Real sun arrives at an angle that changes through the day, so the sheet is a comparison between products, not a forecast for your room.
The two studies in full
Room light during sleep (Mason and others, PNAS, 2022). Twenty healthy young adults, in two parallel groups. One group slept a night under overhead room light at 100 lux, the other in dim light (under 3 lux). Next morning the lit group's insulin resistance was higher, and during the lit night their heart rate was higher and heart rate variability lower; they had more stage N2 sleep and less slow-wave and REM sleep. Melatonin was similar in both groups. It is one night, in a laboratory, in a small group of healthy young adults. It does not measure what a bedroom with a streetlight outside does over months.
Bright light before bed in preschoolers (Akacem and others, Physiological Reports, 2018). Ten children aged 3 to 5 (average 4.3). One hour of bright light at about 1,000 lux before bedtime suppressed melatonin by 87.6 percent on average, and it was still suppressed 50 minutes after the light ended. The dim comparison condition (under 15 lux) was made at home by covering the windows with black plastic and dimming lamps. It is ten children, one exposure, and a light level far brighter than a typical evening room. It does not test window coverings.
For scale: the Canadian Conservation Institute describes 5,000 lux as the light near a window or under a study lamp, and 30,000 lux as average daylight, in its guide to light as an agent of deterioration. The 100 lux of the adult study is ordinary room lighting, and the dim condition is under 3 lux.
7. See it See it
Priya's bedroom window. Known: Priya rents a ground-floor apartment. Her one bedroom window faces east onto the street, 6 ft from the sidewalk. She works three night shifts a week and sleeps until early afternoon, so on those days she sleeps through the whole morning sun. The window is double-hung; inside the frame it measures 34 3/8 in wide at the top, 34 1/4 in in the middle and 34 1/2 in at the bottom, with a depth of 2 3/4 in and a sash lock that stands 3/4 in proud. The trim is 2 1/2 in wide, with 14 in from the top of the trim to the ceiling. The lease allows no holes without written permission, and the landlord's 1 in vinyl mini blinds must stay and be there at move-out.
Light, by the hour: she writes "sun from early morning to late morning; wanted on days off, a problem on sleep days; street at night". Darkness is the first need, privacy at night the second.
Opacity: blackout, because she sleeps by day in an east room. The mini blinds stay closed, but they leak at every slat, as NIOSH notes for blinds.
Edge plan: an inside-mount shade would leave a gap down each side (3/16 in each side at the one maker whose figure we have) and the sash lock eats into the 2 3/4 in depth. An outside-mount blackout shade overlapping the trim, with blackout curtains over it, would cover the edges best, but both need brackets above the frame. Her plan: ask the landlord in writing for a no-drill bracket or two small holes; until the answer comes, keep the blinds closed, use an eye mask, and put a temporary blackout cover over the window.
Assumed: that no children live or visit, so the blinds' cords are not a child hazard here (her assumption).
Open: whether the landlord will allow a no-drill bracket, settled by her written request; whether a tension rod will hold inside a frame with a sash lock, settled by the rod maker's depth and load figures. Under these assumptions the plan potentially gives a dark room on sleep days; how dark is settled by the hand test at noon once it is up.
- Coping with the night and evening shifts: sleep, NIOSH: the hand-in-front-of-your-eyes test and the bedroom-to-bathroom path, in four short paragraphs.
- Light control and privacy, Hunter Douglas: photographs of light filtering against room darkening, and the side-channel answer to light gaps.
- View Through Simulation Tool, Hunter Douglas Architectural: switch between light and dark fabrics at the same openness and watch the view change.
- What affects view-through?, Draper: a short explanation of openness, color and weave, with photographs.
8. Practice Practice
Minimum: one window: its light by the hour written down, an opacity chosen, and for a bedroom an edge plan in one line. Time: about 30 minutes, spread over the hours that matter, plus 5 minutes for the dark test. Materials: the What each window needs sheet or paper, a pencil, your phone's clock, and a sample of the fabric you are considering if you have one.
- Write the light by the hour. For the window, note when direct sun or bright sky reaches it, and next to each time whether that light is wanted or a problem. Put it in the light wanted column of the needs sheet.
- Trace any glare. At the hour the glare happens, sit where it is a problem and find the window, and the part of the window, behind it. Write the time, the seat or screen and the window in the glare column.
- Choose the opacity. From the four words, pick the one that serves the first-ranked need. Write it in the opacity column of the Options for each window sheet, with one line on what it will not stop.
- Do the dark test in a bedroom. At the hour someone sleeps there, close what is there now, turn off the lamps, and hold your hand in front of your face. Then look at each edge of the window and note where light shows: sides, top, bottom, middle.
- Write the edge plan. One line naming the mount and what covers each edge. If a hole is needed and you rent, note the question for the landlord; Hardware and installing says what to ask.
A sample at the window. If you have samples of two fabrics, tape each to the glass at the hour of the problem and look at them from the seat or the bed. A pale sample that glows white in full sun tells you it will let more light into the room than its openness suggests. For a solar shade, compare the dark and light faces of the same openness, and note which keeps more of the view. Test it
9. Your windows Your windows
10. Check your work Check your work
Criteria
- Does each window have its light written by the hour, with each time marked wanted or a problem?
- Is any glare traced to a named window, at a named hour, from a named seat or screen?
- Does each window have one of the four opacity words, with what it will not stop?
- Does each bedroom window, or any window where darkness is a need, have an edge plan that names every edge?
- Is anything that needs a hole or a permission marked as a question, with who answers it?
Worked example
Priya's survey, checked against the criteria (fictional). Light by the hour: written, with the morning sun marked a problem on sleep days. Glare: none at a screen; the problem is darkness, so the glare column says "none". Opacity: blackout, with "edges still leak" beside it. Edge plan: outside-mount blackout shade overlapping the trim, curtains over it, pending the landlord's written answer; interim, blinds closed, eye mask, temporary cover. Questions: the no-drill bracket, to the landlord in writing; the tension rod's depth and load, from its maker. Every criterion is met. Whether the room will be dark enough is not: that is the hand test, once the covering is up.
Common mistakes
- Buying blackout for glare. Blackout darkens the room and takes the daylight and view with it. For glare at a screen, a light-filtering or solar shade, or moving the screen, usually keeps more of what you want.
- Treating "blackout" as a dark room. The fabric is only one part. If the plan does not name the edges, the room will show a bright frame of light round the shade.
- Tracing glare at the wrong hour. Glare at 8 a.m. is not visible at noon, and winter glare is not visible in July. Be there when it happens, and look again in another season.
- Choosing a solar shade by openness alone. Color changes visible light and view more than the openness number suggests. Read the visible transmittance.
- Reading a study as a promise. The light and sleep studies describe small laboratory groups. They do not say what your room will do for you.
What is still unresolved
This chapter settles the opacity and the edge plan, not the product or the size. The kind of covering is chosen in Curtains, shades, blinds and shutters; the lining that turns a curtain into room darkening or blackout in Fabric, linings and fading; the sizes that close the gaps in Measuring for blinds and shades and Measuring for curtains. Whether you may put up a bracket is the landlord's or the association's answer, and Hardware and installing says how to ask. How dark the room actually gets is settled by the hand test after it is up. Your sleep is a question for a doctor.