Colour temperature an important consideration for LED street lamp lighting

Just a few hours ago, I emailed off this letter to both Hobart and Burnie city councils, hoping to encourage them to select warm white LED light arrays for their street lamps. Judging from what I've seen in here in Australia and also in New Zealand towns and cities, most are receiving the LED default option: daylight white. The result is this:

A night time lighting comparison in Hobart, Tamania. HPS stands for (high pressure sodium), and is an older and common lighting technology, also referred to as sodium-vapor.

Cold, glary and excessively bright to our blue light sensitive eyes...not the right ambience for our towns and cities. I'm sharing the letter hoping that a few might stuble upon it: with the switch to LED lighting en-masse now's the time for our local governments to require that their street lamp lighting contractors use 2600K (kelvin) or 3000K warm white LEDs. Ideally, a diffuser or frosted shade would be fitted as LED implementations are often glary.


Email to the Hobart City Council's Smart and Sustainable City Unit, 26th September 2021.

I wrote to the council a number of years ago at the beginning of the cities LED street lamp roll-out. Having been away from Hobart for years now and recently returned, I see that many more LED lamps have replaced the HPS (high pressure sodium) units formerly used around the city.

My suggestion to the council then, and now again, is that the colour balance and brightness of the LED lamps that are replacing our HPS units is not optimal.

Whereas the HPS lamps emit a warm light, more similar to a candle or fire - and are thus more suitable for night lighting - , the cool/daylight white LEDs currently being fitted in Hobart and surrounds emit blue light that our eyes are very sensitive to.

You can test this yourself at home: compare a 'warm white' 2600K or 3000K light bulb for lighting a room at night as opposed to a 5000 or 6000K daylight or cool white light. Which one feels more comfortable? Even tech manufacturers have realised that there are problems with blue light emitting LEDs at night: if you've got a recent smartphone you'll find in the settings a 'night mode' that changes the colour of the screen to be more suitable for night use by making the colours more warm.

The solution? Council, for the continued phase-in of LED street lamp lighting in Hobart, could request that its contractors use warm white LED arrays (2600 or 3000K). I don’t imagine that this would cost more, nor would it affect the energy efficiency gains of switching to LED lighting.

The result? Cosier, less intrusive street lighting for the city, making our urban environment a nicer feeling place to be at night.

Hobart would be in a minority of cities in Australia and New Zealand that have made this distinction. My place of residence in New Zealand, Wairoa, successfully made the transition in 2020, prompted by letters such as what I’m writing to you and also following advice from a lighting expert at the International Dark-Sky Association.

Further information:

Dark Sky Association LED practical guide: https://www.darksky.org/our-work/lighting/lighting-for-citizens/led-guide/

For the science inclined among you. The kruithoff curve shows what colour temperature of lighting is appropriate for human eyes at different light levels. Simply put, the optimal colour of lighting for an office used during the day is very different to what is suitable for a home at night or our city streets. https://en.wikipedia.org/wiki/Kruithof_curve

Thanks in advance for your consideration.

Edit, 11th November 2021:

I received this response from an engineer at City of Hobart council on the 4th of October. No response from Burnie City Council yet...

Hi Damien,

Thank you for your email. I agree completely and have been having the same argument with TasNetworks for some time. Unfortunately, Council does not have control of the street lights except in very limited circumstances.

Over 90% of our street lights are installed and maintained by TasNetworks. We have been receiving quite a few complaints about the brightness of street lights since the LEDs have started replacing HPS lights. In these cases we may put up a shield to give some relief to the affected resident, but this does not reduce the overall glow in the city from too-white lights.

TasNetworks has adopted 4000 K+ lighting across the street lighting network in Tasmania as these "cooler" white lights are required on certain road types, for visibility.

I am continuing to work with TasNetworks to attempt to find a solution and will use your email (anonymised) as an example next time I bring this up with them.

Damien

Damien

Oceania