每日彙整: 2017-06-21

樹莓派、樹莓派之教育、部落格訊息

夏至

夏至‧宋‧張耒

長養功已極，大運忽云遷。人間漫未知，微陰生九原。
殺生忽更柄，寒暑將成年。崔巍干雲樹，安得保芳鮮。
幾微物所忽，漸進理必然。韙哉觀化子，默坐付忘言。

 

時遇『夏至』日，恰好認識長養功極、寒暑成年之

太陽光

太陽光，廣義的定義是來自太陽所有頻譜的電磁輻射。在地球，陽光顯而易見是當太陽在地平線之上，經過地球大氣層過濾照射到地球表面的太陽輻射，則稱為日光。

當太陽輻射沒有被雲遮蔽，直接照射時通常被稱為陽光，是明亮的光線和輻射熱的組合。世界氣象組織定義「日照時間」是指一個地區直接接收到的陽光輻照度在每平方公尺120瓦特以上的時間累積[1]。

陽光照射的時間可以使用陽光錄影機、全天空輻射計或日射強度計來記錄。陽光需要8.3分鐘才能從太陽抵達地球。

直接照射的陽光亮度效能約有每瓦特93流明的輻射通量，其中包括紅外線、可見光和紫外線。明亮的陽光對地球表面上提供的照度大約是每平方米100,000流明或 100,000勒克司。陽光是光合作用的關鍵因素，對於地球上的生命至關重要。

成分

太陽的太陽輻射光譜與溫度5,800K的黑體非常接近。其中約有一半的電磁頻譜在可見光的短波範圍內，另一半在近紅外線的部分，也有一些在光譜的紫外線[9]。當紫外線沒有被大氣層或其他的保護塗料吸收，它可能導致皮膚的曬傷或觸發人類皮膚色素的自我調整變化。

光譜在100至106奈米的電磁輻射不斷的轟擊地球大氣層，按波長的升冪排列，它們可以分成五個區域[10]：

  • 紫外線C（Ultraviolet C）或UVC的範圍跨越100至280奈米。紫外線這個名詞意味著輻射的頻率比紫色還高（因此人的眼睛看不見它）。由於會被大氣層吸收，因此只有非常少的量能夠抵達地球的岩石表面。這種輻射光譜的特性是有殺菌力，和使用為殺菌燈。
  • 紫外線B或UVB的範圍從280至315奈米。它也被大氣層大量的吸收，並且和紫外線C一起導致光化學反應製造出臭氧層。
  • 紫外線A或UVA的範圍從315至400奈米。一般認為它對DNA的傷害最小因此常用來曬黑和做為牛皮癬的PUVA療法。
  • 可見範圍或光的範圍從400至700奈米。如同名稱所暗示的，這是肉眼可以看見的範圍。
  • 紅外線的範圍從700奈米至106奈米[1（mm）]。在到達地球的電磁輻射中它們是很重要的一部分，依據波常可以分成三種類型：
    • 紅外線-A：700奈米至1,400奈米
    • 紅外線-B：1,400奈米至3,000奈米
    • 紅外線-C：3,000奈米至1毫米

在大氣層之上和表面的太陽輻照度光譜。

 

！日光光譜正是見顏顯色故鄉◎

Spectral composition of sunlight at Earth’s surface

The Sun’s electromagnetic radiation which is received at the Earth’s surface is predominantly light that falls within the range of wavelengths to which the visual systems of the animals that inhabit Earth’s surface are sensitive. The Sun may therefore be said to illuminate, which is a measure of the light within a specific sensitivity range. Many animals (including humans) have a sensitivity range of approximately 400–700 nm,[29] and given optimal conditions the absorption and scattering by Earth’s atmosphere produces illumination that approximates an equal-energy illuminant for most of this range.[30] The useful range for color vision in humans, for example, is approximately 450–650 nm. Aside from effects that arise at sunset and sunrise, the spectral composition changes primarily in respect to how directly sunlight is able to illuminate. When illumination is indirect, Rayleigh scattering in the upper atmosphere will lead blue wavelengths to dominate. Water vapour in the lower atmosphere produces further scattering and ozone, dust and water particles will also absorb selective wavelengths.[31][32]

Spectrum of the visible wavelengths at approximately sea level; illumination by direct sunlight compared with direct sunlight scattered by cloud cover and with indirect sunlight by varying degrees of cloud cover. The yellow line shows the spectrum of direct illumination under optimal conditions. The other illumination conditions are scaled to show their relation to direct illumination. The units of spectral power are simply raw sensor values (with a linear response at specific wavelengths).

 

人間照明標準對象和模仿榜樣☆

Illuminant D65

CIE Standard Illuminant D65 (sometimes written D65[1][2]) is a commonly used standard illuminant defined by the International Commission on Illumination (CIE).[3] It is part of the D series of illuminants that try to portray standard illumination conditions at open-air in different parts of the world.

D65 corresponds roughly to the average midday light in Western Europe / Northern Europe (comprising both direct sunlight and the light diffused by a clear sky), hence it is also called a daylight illuminant. As any standard illuminant is represented as a table of averaged spectrophotometric data, any light source which statistically has the same relative spectral power distribution (SPD) can be considered a D65 light source. There are no actual D65 light sources, only simulators. The quality of a simulator can be assessed with the CIE Metamerism Index.[4][5]

The CIE positions D65 as the standard daylight illuminant:

[D65] is intended to represent average daylight and has a correlated colour temperature of approximately 6500 K. CIE standard illuminant D65 should be used in all colorimetric calculations requiring representative daylight, unless there are specific reasons for using a different illuminant. Variations in the relative spectral power distribution of daylight are known to occur, particularly in the ultraviolet spectral region, as a function of season, time of day, and geographic location.

— ISO 10526:1999/CIE S005/E-1998, CIE Standard Illuminants for Colorimetry

Spectral power distribution of D65.