Talk:Candela per square metre

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Misc[edit]

Need to add the nit-rating range for cell phone displays and for digital cameras that have displays, especially real-time displays - most are unreadable under direct sunlight, but the manufacturer literature never gives a nit rating.—Preceding unsigned comment added by 68.93.135.160 (talkcontribs) 00:08, 13 October 2009

I'm not sure that material is encyclopedic. Wikipedia is not for product reviews or ratings.--Srleffler (talk) 05:55, 13 October 2009 (UTC)

Spec for Daylight readable[edit]

The article states that 800 nits is daylight readable. Others cite 500 nits as daylight readable. eg [Clear Sunlight.pdf]—Preceding unsigned comment added by 109.207.29.2 (talk) 12:09, 12 July 2010 (UTC)

Who is deprecating "nit"?[edit]

The introduction of the article states that the term nit is deprecated. It should be added who is deprecating it. --93.223.19.248 (talk) 14:15, 24 August 2011 (UTC)

Agreed. I don't know the answer. In some sense, all non-SI units are "deprecated" by international standards bodies, but perhaps something more specific is implied here.--Srleffler (talk) 03:40, 25 August 2011 (UTC)

Invalid units conversions ?[edit]

I don't see how one can apply a dimensionless constant to convert both to Lamberts and also to Foot-Lamberts ! There must be an implicit "at a distance of one foot", surely !

Percieved brightness must also take into account the size and position (angle + distance) of the observer's eye. Only a fraction of the light emitted will reach the eye. If the light is 'focussed' into a beam, it can appear brighter (or use less power), within a narrower range of viewing angles.

I basically distrust this article, and also manufacturers' claims.

--195.137.93.171 (talk) 16:49, 24 September 2012 (UTC)

Candela per square metre, lamberts, and Foot-lamberts all have the same physical dimensions, so the constants to convert between them are naturally dimensionless. Luminance always has dimensions of luminous intensity per unit area.
You're exactly correct that perceived brightness must take into account the size and position of the observer's eye, and it does: the angular spread of the light enters through the candela, which is luminous flux (in lumens) per unit solid angle. If you focus the light into a narrower beam, the luminance does not increase, because the decrease in diameter of the beam is exactly compensated for by the decrease in solid angle subtended. In fact, in an ideal optical system where no light is lost, luminance is conserved.
The total luminous flux from an object that reaches an observer's eye is equal to the object's luminance, integrated over the surface area of the object and over the solid angle the eye's pupil subtends at the location of the object. (This gets complicated if the object is not flat or the luminance is not uniform. I'm glossing over some details here.)--Srleffler (talk) 17:22, 24 September 2012 (UTC)