Cooling a Kahului office without mirrored windows

Two ways film cuts heat

Sunlight reaches an office in three parts: UV, visible light and infrared. UV is a small share of the energy, and visible light and infrared carry most of the heat. Film deals with that in one of two ways.

Reflective film has a metal layer that bounces a lot of the sunlight back out, visible and infrared alike, before it reaches the room. It works, and it’s what gives some office buildings their mirror face.

Spectrally selective film treats the parts of sunlight differently. It lets more of the visible light through and holds back more of the infrared, so it cuts heat while the room stays bright and the glass looks close to normal, with low reflection inside and out. It does part of its work by absorbing, so the glass itself runs warmer, which is one reason the glass gets checked before a film is chosen. Can window film crack glass? explains that check.

Both kinds block most of the UV that fades carpet, furniture and anything displayed near the glass.

The mirror, by day and by night

By day, reflective film gives the outside of the building a mirror face. Staff see out, and the street sees the parking lot reflected back.

After dark, with the lights on inside, it flips. The inside of the glass becomes the mirror, so staff see themselves, and the street can see into the lit office. Reflective film is a daytime effect, not night privacy. A ground-floor office still needs blinds after dark, whatever film is on the glass.

The look from the street is also what landlords and property owners care about, and many leases and property rules control changes to exterior glass. Hawaii’s window tint law, with its ban on mirrored film, is a vehicle law and doesn’t cover buildings. For an office, the lease and the property’s own rules decide what the glass may look like, so ask before choosing a film.

Screen glare

Glare on monitors comes from two places: direct sun on the screen or desk, and a bright window beside or behind the screen. Film tones down the brightness of the whole window, which reduces the contrast that makes screens hard to read. A darker film cuts more glare and darkens the room; a lighter one keeps more daylight and cuts less glare. The right balance depends on the room. A conference room with a screen at one end wants more glare control than a lobby does.

When the sun is low and shining straight onto a desk, no film takes that away completely. Blinds, or turning the desk, do the last part.

Do the worst windows first

Walk the office on a sunny afternoon and note:

• which desks get direct sun, and from what time
• which conference room nobody books after lunch
• which screens are hard to read, and when
• where the air conditioning struggles to keep up

That’s the glass to film first. Use the film you’d want for the whole building, so later phases match inside and out. Glass shaded by overhangs, trees or the next building may need nothing. Interior glass for conference rooms and partitions is a different job, handled with frosted or decorative film; the decorative and privacy film page covers it.

Practical points for an office

• Installs go room by room and are scheduled around business hours.
• One film across each side of the building keeps the outside uniform.
• Old, purple or bubbled film comes off before new film goes on.
• Tell the cleaning crew: the filmed side is cleaned with a soft cloth and a non-ammonia cleaner, never a blade or a scrub pad.

If the ground floor is retail, the guide to storefront safety film covers display glass and entry doors.

Getting a quote

Kahului is about 8 minutes from the shop in Wailuku, and office film is measured and installed on site. It’s quoted in writing after a measure, with no online price or checkout. Send the address, which rooms are the problem and when, photos of the windows and any lease rules on the glass through the quote form, or call (808) 707-7064. The commercial window film page covers the film types, and the Wailuku and Kahului page covers the area.