Brighter isn’t always lighter

Which of these stations is better lit?

Canada Line Station

TransLink system lighting standard for subway platforms: 4 foot-candles

IMG_2524 - Washington DC - WMATA Metro Chinatown Station - After Genesis concert
WMATA system lighting standard for subway platforms: 10 foot-candles

Believe it or not, WMATA hardly has the darkest stations in the business. I was amazed to learn recently that Vancouver’s transit agency specifies platform lighting 60% dimmer than WMATA’s: their standard is 4 foot-candles, vs. 10 foot-candles for WMATA. I usually read when I’m aboard transit, and whereas I have to seek out light on Metro subway platforms, I’ve never thought twice about the brightness on TransLink platforms (admittedly, I’ve spent much less time on the latter, partly due to the automated system’s startlingly low headways).

The difference is that TransLink also specifies high-reflectance, light-colored walls and floors, and directs light into occupied areas so that they feel much brighter. With “passive illumination,” it’s not just how much light is used, but also what the space does with that light. Seemingly minor increases in reflectance for surfaces like walls and ceilings (particularly for indirect lighting scenarios) proportionately increase the brightness one can achieve with a given amount of light.

By comparison, much about the classic Metro station design thwarts attempts at improving lighting — and intentionally so, in fact. Our standards of brightness have increased, partly because illumination has become so cheap. Yet the dark material palette chosen for the stations (unpainted concrete walls and ceilings, burgundy tiles, chocolate brown panels, even the bronze railings) absorb both what little light is added and dirt, which further darkens the stations over time.

Metro points to the efforts that it’s taken recently, including regular power cleaning of the concrete station vaults, existing efforts to add fixtures, and a system-wide re-lamping with more modern (and thus brighter and more energy-efficient) equipment. The fruits of these can be seen at stations like Judiciary Square, which does indeed seem like a beacon of light compared to others in the system.

Yet using more reflective materials can also improve station lighting. That’s the gist behind recent changes that Metro announced to the Bethesda station (previous GGW discussion here), like replacing brown metal panels and concrete walls with brushed metal and clear glass. These changes will definitely help, but a more comprehensive approach could look at other changes that can improve lighting without dramatically impacting the stations’ canonical appearance.

  • A clear polymer coat (not paint) could increase reflectance of existing concrete surfaces, reduce porosity and thus the problem of embedded dirt, and make cleaning easier. Painting the station vaults has proven controversial throughout Metro’s history: Zach Schrag’s book The Great Society Subway points to a 1968 disagreement between the designers Harry Weese and William Lam as to whether to paint the vaults, and notes Weese’s “commitment to ‘pure structure in plain concrete’ ” in criticizing a 1990s decision by WMATA to paint some vaults. Yet materials advances now mean that light reflectance surprisingly has less to do with color as one might expect: a darker color with a slight gloss reflects more than a brighter color with a dull finish.
  • The existing fluorescent tubes are recessed within wells that are out of sight, beyond the platform edge or between the tracks. Since these surfaces are so close to the light sources, small changes here will result in big changes throughout. Cleaning and brightening surfaces within these wells, adding reflectors below the tubes to “catch” light that’s currently pointing downwards, moving wire conduits so that they’re below lights instead of blocking them, and replacing bronze-colored diffusers above the between-track tubes with clear plastic diffusers, will all result in more light to reflect upwards into the station.
  • Acoustic panels in coffer recesses can be brighter. These panels cover a surprising amount of the vaults’ surface area, but because they’re literally in the concrete’s shadows, we don’t tend to notice them very much. These, too, accumulate dirt and dust over time, and as they’re replaced their reflectance could be increased. The new Rosslyn entrance has highly reflective panels embedded within its coffers, which I didn’t even notice the first few times I walked through it.
  • Similarly, the drop-ceiling tiles underneath station mezzanines can be replaced with tiles that reflect more light. Given the low ceiling heights in these spaces and the fact that they’re largely hidden from view, a more ambitious upgrade could replace these with ceiling tiles with embedded LED lamps, reducing both shadows and glare in these areas while improving efficiency over the existing can lights. LED ceiling tiles might sound gaudy, but look no different than the fluorescent panels embedded in most office drop ceilings.

Attention to these details can ensure that the maximum possible amount of light is available within Metro’s subway stations, improving energy efficiency, safety, comfort, and accessibility without altering their iconic appearance.

[A version of this is cross-posted at Greater Greater Washington]